ELEARNI NG FOR THE OPERATORS OFWASTEWATER TREATMENT
VOLUME 6
ORGANISING A LABORATORY FOR WATER & WASTEWATER ANALYSIS
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6.
ORGANIZING A LABORATORY FOR WASTEWATER ANALYSIS 6.1 PROCESS CONTROL, SAMPING & TESTING 6.1.1 Wastewater sampling 6.1.1.1 6.1.1.2 6.1.1.3 6.1.1.4 6.1.1.5 6.1.1.6
6.1.2 6.1.2.1
6.1.3 6.1.3.2 6.1.3.3 6.1.3.4 6.1.3.5 6.1.3.6
Sampling Devices and Containers Preservatives Samples Requiring Special Consideration Sample Types Composite Sampling Procedure Sample Hold Time
Use of Auto Samplers Recommended Sampling Locations for Process Control17
Sampling & Testing in activated sludge process23 Aeration Tank Settling Tank Influent Settling Tank Settling Tank Effluent Return Activated Sludge and Waste Activated Sludge
6.2 DESIGN, INFRASTRUCTURE AND MANAGEMENT 6.2.1 Laboratory services 6.2.1.1 6.2.1.2 6.2.1.3 6.2.1.4 6.2.1.5 6.2.1.6 6.2.1.7 6.2.1.8 6.2.1.9
6.2.2 6.2.2.1 6.2.2.2 6.2.2.3 6.2.2.4 6.2.2.5 6.2.2.6
6.2.3 6.2.3.1 6.2.3.2
Distilled Water Ammonia free Water Carbon-Dioxide-FreeWater Ion-FreeWater Compressed Air Vacuum Hood System Electrical Services Lighting
Housekeeping Laboratory Environment Climate General Cleanliness Washing Dishes Acid Washes Oxidizers
Historical Records Benchsheets Log Book
6.3 LABORATORY BASICS 6.3.1 Measures of Precision 6.3.1.1 6.3.1.2 6.3.1.3 6.3.1.4
6.3.2 6.3.3 6.3.3.1
6.3.4 6.3.4.1 6.3.4.2 6.3.4.3 6.3.4.4 6.3.4.6 6.3.4.7 6.3.4.8
Mean Relative Percent Difference Standard Deviation Relative Standard Deviation
Measures of Accuracy Quality assurance and quality control Quality Assurance System
Elements of quality control Method Blank Laboratory-Fortified Blank Duplicates Calibration Initial Demonstration of Capability Quality Control Sample Control Charts
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6.3.5 6.3.5.1 6.3.5.2 6.3.5.3 6.3.5.4 6.3.5.5
6.3.6 6.3.6.1 6.3.6.2 6.3.6.3 6.3.6.4 6.3.6.5 6.3.6.6 6.3.6.7 6.3.6.8
6.3.7 6.3.7.1 6.3.7.2 6.3.7.3 6.3.7.4
6.3.8 6.3.8.1 6.3.8.2 6.3.8.3
6.3.9 6.3.10 6.3.10.1 6.3.10.2 6.3.10.3
Limits and Levels Instrument Detection Limit Method Detection Level Quantitation Limits Reporting Limits Expression of results
Basic chemistry Using the Periodic Table of the Elements Moles Chemical Compounds Formula Weight Molar Solutions Normal Solutions Milligrams per Liter Solutions Determining Percent Weight of Atoms in Molecules
Weighing Analytical Balances and Weighing Conditions Weighing Containers and Accessories Drying Dishes and Reagents Weighing Procedures for Reagents
Reagents Laboratory-Grade Water Reagent Grades Mixing Reagents
Making acids and bases Stock, standards and standards dillutions Stock Solutions Standard Solutions Standard Dilutions
6.4 MATERIALS AND SET-UP OF EQUIPMENT, INSTRUMENTS AND OTHER DEVICES 6.4.1 Laboratory equipment 6.4.1.1 6.4.1.2
Glassware Miscellaneous Laboratory Equipment73
6.5 WORKING PROCEDURES 6.5.1 Wastewater test methods 6.5.1.1 6.5.1.2 6.5.1.3 6.5.1.4 6.5.1.5 6.5.1.6 6.5.1.7 6.5.1.8 6.5.1.9 6.5.1.10
6.5.2 6.5.2.1
Gravimetric Analysis Titrimetric Methods Colorimetric Methods Visual Methods Electronic Methods pH Measurement Chlorine Residual Testing/Analysis Dissolved Oxygen Testing Biochemical Oxygen Demand Testing Solids Measurement
Spectrophotometry Fundamentals of the technology
6.6 ANALYTICAL METHODS 6.7 SAFETY AND HYGIENE 6.7.1 Personal Protective Equipment 6.7.2 Chemical Storage 6.7.3 Chemical Handling 6.7.4 Chemical Spills 6.7.5 Fire 6.7.6 Ingestion Hazards 6.8 GLOSSARY
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6.9 QUESTIONS & ANSWERS
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6. ORGANIZING A LABORATORY FOR WASTEWATER ANALYSIS 6.1 Process control, samping & testing 6.1.1 Wastewater sampling
In wastewater sampling, the first critical step is to obtain good, untainted, valid information by collecting a representative sample. The second critical step in sampling is to follow a predetermined, user-friendly, well-written sampling protocol. Although it is true that sample type and collection point must always be based on the test requirements and the particular information sought, it is also true that basic guidelines should be used for all sampling activities. Thus, the third critical step in sampling is to follow sampling rules. Sampling rules that should be followed anytime sampling is undertaken include:
• Samples must be collected from a well-mixed location. • Sampling points must be clearly marked and easy to reach. • Safety should always be considered when selecting a sampling point. • Large, nonrepresentative objects must be discarded. • No deposits, growths, or floating material should be included in the sample. • All testing must begin as soon as possible after sample collection. • Samples containing high concentrations of solids or large particles should be homogenized in a blender.
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• Sample bottles and sample storage containers should be made of corrosion-resistant material, have leakproof tops, and be capable of withstanding repeated refrigeration and cleaning after use. • Each sampling location should have a designated storage container used only for samples from that location. • Appropriate safety procedures should always be followed when collecting samples (e.g., rubber gloves, washing after sampling, remaining within guardrails).
6.1.1.1 Sampling Devices and Containers The tools of the trade for sampling performed by wastewater operators (and others) always include sampling devices and containers. It is important to ensure that sampling devices are corrosion resistant, easily cleaned, capable of collecting desired samples safely, and in accordance with test requirements. Whenever possible, a sampling device should be assigned to each sampling point. Sampling equipment must be cleaned on a regular basis to avoid contamination.
Note: Some tests require special equipment to ensure that the sample is representative. Dissolved oxygen and fecal coliform sampling requires special equipment and procedures to prevent collection of nonrepresen-tative samples. Sample containers may be specified for a particular test. If no container is specified, borosilicate glass or plastic containers may be used. Sample containers should be clean and free of soap or chemical residues.
Sample Containers The choice of sample container type, size, and material depends on several considerations, including the volume of sample required, interference problems anticipated, type of testing to be performed, cost and availability, and resistance to breakage. The container requirements should be specified as part of the sampling program. To prevent contamination, sample containers must be cleaned before being filled. New containers are not necessarily clean and must also be washed using prescribed procedures. At a minimum, all containers and caps must be washed in a nonionic and nonphosphate detergent, rinsed well with hot tap water, and then rinsed with distilled water. Preferably, after being rinsed in distilled water, sample containers and caps should be soaked in an acid solution at a temperature of approximately 70 °C for approximately 24 hours and then rinsed with distilled water for a second time.
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Quartz, polytetrafluoroethylene, or glass containers can be soaked in 1:1 nitric acid, 1:1 hydrochloric acid, or aqua regia (four parts hydrochloric acid to one part nitric acid) solutions. Plastic containers should be soaked in 1:1 nitric acid or 1:1 hydrochloric acid solutions. Solvent rinses are required for oil and grease or pesticide sample containers. These should be rinsed with hexane, followed by acetone, and, finally, distilled water. Some container manufacturers certify that their containers are "clean", thus to be used without washing or sterilizing once a new case is purchased. Because oil and grease in wastewater easily adhere to a number of materials, the recommended sample container is a wide-mouth jar with a polytetrafluoroethylene-lined screw lid. The wide mouth allows the technician to rinse the inside walls of the jar with the solvent used in the analysis.
Polyethylene containers
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The jar should be precalibrated because the initial steps of the procedure are performed in the container. In this instance, pvecalibrated means that the jar at whatever volume is premeasured before collecting the sample. Because the initial steps are happening in the sample container, the volume has to be accurately measured and determined prior to adding any solvents. Even if the jar has graduations, the graduations have to be verified as accurate because graduations on sample containers (or even non-class-A glassware) are typically "approximate". Container caps or lids, which can potentially contaminate the sample, can be lined with aluminum foil or polytetrafluoroethylene before being placed on the container. Sampling containers should be prelabeled with the appropriate information and any special information the technician may need regarding the collected sample, such as unusual odors, appearance, or conditions. Sampling containers that contain a preservative are not typically used to collect the sample. Care should be taken not to overfill the sample container when transferring the sample to the sample container to avoid flushing out the preservative. A separate collection device should be used at each sampling location. With the exception of containers to which a preservative has been added and those used for oil and grease, containers should be rinsed with the sample material before collecting the sample. Oil and grease sample containers cannot be rinsed with the sample because of the container preparation and the adherence of oil and grease to the container walls. Sample containers or collection devices that are permanently stained should be discarded.
6.1.1.2 Preservatives Guidelines have been established for preservation of water and wastewater samples. The techniques discussed are intended to provide an overview of options available for the preservation of samples. Refrigeration, pH adjustments, and chemical additions are the primary methods recommended for sample preservation. Again, the aforementioned sources should be referred to for more specific information and legal requirements. The most frequently used means of sample preservation is refrigeration at temperatures near freezing (6 째C) or the use of wet ice. Biological activity is decreased because respiration rates are greatly reduced at low temperatures. Chemical reaction rates and the loss of dissolved gases also are reduced. It is often necessary to combine chemical addition or pH adjustment with refrigeration to ensure effective preservation. Refrigeration at temperatures at or below freezing (0 째C) is an effective long-term preservation method for only some parameters. In addition to killing or slowing the metabolism of microorganisms, freezing of samples has other limitations. To avoid breakage, sample containers must have sufficient head space to allow for the expansion of freezing liquid. Particulate material will solubilize readily while samples are thawing because cell structures rupture when frozen. Samples to be analyzed for suspended or dissolved solids should never be frozen.
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Acid addition is a common method for decreasing both biological and chemical activity. Sulfuric acid (H2SO4) is added to a sample to stop bacterial action; preserving samples for COD and organic carbon analyses are examples of when this application might be used. Sulfuric acid addition combined with refrigeration both preserves and pretreats oil and grease. Acids dissolve particulate matter and, therefore, must be avoided if suspended solids are to be determined. Alkali, typically sodium hydroxide (NaOH), is added to samples to prevent the loss of volatile compounds through the formation of a salt. Organic acids and cyanide are examples of saltcomplexing compounds. Chemicals, including acids and bases, are added to samples to stabilize compounds or stop biological activity. Copper sulfate (CuS04) and mercuric chloride (HgCl2) are two biological inhibitory chemicals commonly used. Zinc acetate phosphoric acid and sodium hydroxide are frequently used as complex-ing agents. The actual addition of chemicals alters the original composition of the sample. It is important to avoid adding chemicals that contain elements for which the sample will be analyzed. For example, samples being collected for nitrogen analyses should not be preserved with nitric acid; samples for sulfate should not contain sulfuric acid. In many instances, the volume of preservative must be taken into account to properly establish the concentration of contaminants. The combinations of possible cross-contaminations are great; however, they can be avoided by using common sense and carefully planning the sample program. Sample preservation can be replaced with an alternative procedure with the proper regulatory approval. Currently, biomonitoring is an important tool for monitoring facility operational performance.. Containers should be made of plastic or glass. Samples should be cooled to 6 째C, and the holding time is 36 hours.
6.1.1.3 Samples Requiring Special Consideration Some samples need special consideration during sample collection. For example, microbiological samples need to be collected in sterile containers. Caution should be used when collecting and analyzing samples for phosphorus. Phosphorus is everywhere and can easily contaminate samples. It is important to never touch the inside of a sampile bottle or lid with bare hands. Gloves should be worn and extra caution should be exercised when handling sample bottles, scoops, and so on. The containers and sample scoop should be prewashed with 1:1 hydrochloric acid and rinsed with distilled water. Additionally, if oxidants such as chlorine are used for disinfection, reagents capable of neutralizing the disinfectant need to be added to the sample container.
6.1.1.4 Sample Types The two basic types of samples are grab samples and composite samples. The type of sample taken depends on the specific test, the reason why the sample is being collected, and
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requirements stated in the plant discharge permit. A grab sample is a discrete sample collected at one time and one location. Grab samples are primarily used for any parameter whose concentration can change quickly, such as dissolved oxygen, pH, temperature, and total chlorine residual. They are representative only of the conditions at the time of collection. A composite sample consists of a series of individual grab samples taken at specified time intervals and in proportion to flow. The individual grab samples are mixed together in proportion to the flow rate at the time the sample was collected to form the composite sample. The composite sample represents the character of the water/wastewater over a period of time.
Grab Samples A grab sample is one that is taken to represent one moment in time and is not mixed with any other samples. A grab sample is sometimes called an individual or discrete sample and will only represent sample conditions at the exact moment it is collected. Grab samples are often useful under certain situations in which composite samples would not be adequate. Examples of these situations include the following: • The characteristics of "slug" discharges must be determined by grab samples to help identify the source and assess potential effects on treatment processes. These discharges are often noticed visually by a plant operator performing routine duties; the duration typically is unknown. • Numerous grab samples are used to study variations and extremes in a waste stream during a period of time. Composite samples do not reveal waste variations over time because of the nature of the samples. Composites tend to average both short-duration, high-strength discharges and long-duration, low-strength discharges. The significance of this depends on the vohime of flow at the time of collection. Composite samples tend to dilute short, high- or low-strength discharges that could affect a treatment plant's performance, but go unnoticed. Taking both composite and sequential discrete samples can be advantageous in periodically testing for waste variations over a specific timeframe. • Grab samples can be used if the flow to be sampled occurs intermittently for short durations. • Grab samples can be used if the flow composition to be sampled is reasonably constant. Of course, this assumption must be verified with multiple samples over an adequate time period to determine if there really are variations in flow composition. • Grab samples must be used if the constituents to be analyzed are unstable or cannot be preserved and, therefore, must be analyzed immediately or stored under special conditions.
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Examples of these parameters include oil and grease, pH, chlorine residual, dissolved oxygen, bacteriological tests, purgeable organic compounds, and phenols.
Composite Samples A composite sample is prepared by combining a series of grab samples over known time or flow intervals. A composite sample shows the average composition of a flow stream over a set time or flow period if the sample is collected proportional to flow. These samples can be collected manually and mixed together or they can be collected by automatic sampling equipment. The samples taken by automatic composite sampling equipment may be composited as they are collected into one large receptacle. At most WWTPs, composite samples are required under regulatory permit requirements for most constituents that do not require immediate analyses. Typical composite sampling is required for parameters such as BOD, TSS, ammonia nitrogen, and total phosphorus. Results from analyses used to calculate plant and process loadings (such as organic loading or F: M) should always be made from composite samples. This practice is important in ensuring that data obtained from a slug or spike flow, using a single grab sample; do not bias the information or provide misleading data. Two different types of composite samples are generally used. These are known as fixed-volume or flow-proportional composites. MORE Fixed-Volume Composite Samples The fixed-volume composite, also called a time composite, is the simpler type of composite sample. In fixed-volume composite sampling, a series of individual grab samples, all having the same volume, are collected at equally spaced time periods. Fixed-volume composite samples will only give an accurate representation of average composition of flow if flow does not vary during the sampling period. This is not often the case in typical treatment plants, even when systems are equipped with flow-equalization tanks to dampen flow variations. The fixed-volume composite sample is more appropriate for sampling activated sludge aeration basins, sludge solids in digesters, constant-flow streams, and sludge cakes from dewatering equipment. The total volume of the composite sample required depends on the types of analyses that must be performed on the sample. The number of individual grab samples required to make up the composite sample depends on the timeframe of the sampling event and other factors such as regulatory requirements and the degree of accuracy. U.S. EPA allows time-proportional sampling and in its standards requires 15-minute intervals (96 samples per day). Generally, the more individual samples collected, the better the composite will represent the flow stream. For example, 24
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samples of 500 mL each collected to form a 12-L composite will better represent the flow stream than 12 samples of 1 L each. To calculate the volume of each individual sample that must be collected and combined into one composite sample, the time interval and total composite sample size required must first be determined. For example, if a 1-L composite sample must be collected during a 24-hour period, with sampling intervals every 2 hours, the calculation is as follows: Number of samples collected = Total hours/Sample frequency 24/2 = 12 samples Volume of each sample = Total sample volume/Number of samples 1000 mL/12 samples = 84 mL/sample Allowing for surplus sample, the volume should be rounded up to 100 mL. When rounding up, the container size and accuracy of collection volume must be considered. When individual grab samples are combined as a composite, they must be transferred quickly, first from the collection point to the sample measuring device and then to the composite container, while continuously being mixed. Agitating the sample in this manner prevents settling and reduces sampling error. This process is best accomplished using automatic composite-sampling equipment, which eliminates the measure-transfer step.
Flow-Proportional Composite In flow-proportional sampling, the sample volume collected varies based on the flowrate of the waste stream being sampled. Either the volume of each individual grab sample or the sample frequency is varied in direct proportion to flowrate. To be correct, a flow-proportional composite sample must be based on accurate measurements of the waste stream flowrate.. A flow-proportional composite sample is more representative of the waste stream than a fixedvolume sample because it takes into account variations in wastewater characteristics that result from fluctuations in flow. Many NPDES permits require that flow-proportional samples of plant effluent be collected. Typical parameters that are often analyzed in flow-proportional composite samples include suspended solids, BOD, ammonia nitrogen, and total phosphorus.
Variable-Volume Technique If manual sampling is used to create a flow-proportional composite sample, the variable-volume technique is typically the easier and more practical way to collect the-sample. With this technique,
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the volume of each sample collected is based on the flowrate of the waste stream at the instant the sample is collected. An example of one procedure used to manually collect a variable-volume composite sample is given here. The procedure estimates the volume of sample that should be collected during each sampling event, as follows: (1) Determine the minimum composite sample volume, in milliliters, needed to perform all of the desired analyses. Refer to Standard Methods or other references to determine the required sample volumes for each analysis. Keep in mind that the minimum sample volumes recommended in Standard Methods may not always be large enough. For example, larger sample volumes will be needed for the TSS test when the effluent is clean then when it contains higher quantities of solids. Additional volumes of sample should be collected to allow for duplicate quality control analysis or spillage of the sample. (2) Ensure that the sampling container is large enough to hold the desired sample volume. If the sampling container overflows during compositing, the entire contents should be discarded and sampling should be started over. (3) Determine how many samples will be collected during the sampling period. Many discharge permits define a composite sample as a total of four samples taken 2-hours apart. In this instance, samples may be collected at 8 a.m., 10 a.m., 12:00 p.m., and 2 p.m. Many discharge permits define a 24-hour composite sample as a minimum of eight samples evenly spaced over a 24-hour period. In this instance, one sample could be collected every hour or once every 3 hours (or with some other frequency) as long as the samples are taken at even intervals during a 24-hour period. In either instance, the minimum sample volume that should be collected at each sampling time is 100 mL. Smaller sample volumes may not be representative. Before collecting samples for permit compliance, the discharge permit should be checked to ensure that all permit requirements are met. (4) Determine the average daily flow for the facility. Flow varies daily and may be very different on weekends compared to during the week. An estimated average daily flow number should be chosen that is representative of flows observed over the previous week or two. (5) The last piece of information needed to calculate sample volumes is instantaneous flow at the time of sampling. This number will not be known until the sample is taken. (6) Prepare a log sheet for tracking the time of sample collection, the instantaneous flow rate at the time of sampling, the volume of sample collected, the average daily flow used for the sampling calculation, the actual average daily flow, and the initials of the person collecting each sample. An example using the aforementioned procedure is presented here. For the example, an 8-hour, flow-
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proportional composite sample is to be taken at a sampling interval of once every 2-hours (four samples all together). The parameters to be analyzed are BOD, TSS, and ammonia-nitrogen (NH3-N). The daily average flow at the treatment plant is 5677 m3/d and the minimum measurable reading is 378.5 m3/d. If the plant flowrate varies significantly on a seasonal or other basis, it may be necessary to recalculate the aforementioned steps. If the flow is not known or is intermittent, as is commonly the case with industrial waste streams, equal volumes of samples can be collected and stored. After hourly flowrates are obtained, a composite sample can be prepared by mixing the proportion of each sample that corresponds to the flow at the time of collection. For example, 1-L samples can be collected at hourly increments, and the flow can be recorded each time a sample is taken. After the sampling period has ended, the samples can be proportioned according to the recorded flow each time a liter sample was taken. This procedure requires several clean containers and a large storage area. Also, this procedure must be carefully performed to make sure all of the samples are well mixed before subsampling. This method is better suited to use with automatic sampling equipment, which can collect hourly discrete samples in separate bottles for later composite sampling
Variable-Frequency Technique In variable-frequency, flow-proportional composite sampling, the volume of sample collected stays constant, but the time interval between samples or frequency in which the samples are collected varies. The sample intervals are proportional to the measured flows. Variable-frequency, flowproportional composite samples are rarely used with manual sampling but are often used with automatic sampling equipment. To collect these types of samples, an automatic sampler is coupled to a flow meter that collects each sample after a preprogrammed amount of wastewater flows past the sampling point. To determine the frequency of each individual sample, the average plant flow, individual sample size, and total composite sample required must be known or accurately estimated. A procedure for determining the wastewater flow volume for each sample interval is given here. (1) Determine the final composite sample volume required. This is determined based on the required volume needed to test all of the parameters to be analyzed. (2) Divide the total composite sample volume by a realistic and convenient volume selected for each sample. This value represents the number of samples to be collected each day.
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(3) Divide the average daily flowrate of the waste stream by the number of samples to be collected. This number should be adjusted upwards to greater than 100 to be statistically significant for a 24-hour period. This number equals the volume of wastewater that must pass through the sampling-point measuring device before a sample is collected. It can be seen from this procedure that the faster a specific quantity of wastewater passes the sampling point, the more frequently a set-volume sample must be collected.
6.1.1.5 Composite Sampling Procedure When preparing oven-baked food, a cook pays close attention to setting the correct oven temperature. Usually, the cook sets the temperature at the correct setting and then moves on to some other chore— the oven thermostat makes sure that the food is cooked at the correct temperature, and that is that. Unlike the cook, in wastewater treatment plant operations the operator does not have the luxury of setting a plant parameter and then walking off and forgetting about it. To optimize plant operations, various adjustments to unit processes must be made on an ongoing basis. The operator makes unit process adjustments based on local knowledge (experience) and on lab test results; however, before lab tests can be performed, samples must be taken. Because knowledge of the procedure used to process composite samples is important (a basic requirement) to the water/wastewater operator, the actual procedure used is presented below.
• Determine the total amount of sample required for all tests to be performed on the composite sample. • Determine the average daily flow of the treatment system.
Note: Average daily flow can be determined by using several months of data, which will provide a more representative value.
• Calculate a proportioning factor
Note: Round the proportioning factor to the nearest 50 units (e.g., 50,100, 150) to simplify calculation of the sample volume.
• Collect the individual samples in accordance with the schedule (e.g., once per hour, once per 15 minutes). • Determine flow rate at the time the sample was collected.
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• Calculate the specific amount to add to the composite container • Mix the individual sample thoroughly, measure the required volume, and add to composite storage container. • Refrigerate composite samples throughout the collection period.
6.1.1.6 Sample Hold Time Regardless of the hold time, samples should be analyzed as soon as possible. The fresher the sample is the less chance of it changing chemically, biologically, or physically, resulting in a more accurate analysis. For a grab sample, the holding time begins at the time of collection. For a 24hour composite sample collected with an automated sampler, the hold time begins when the last sample has been collected. For a set of grab samples composited in the field or laboratory, the holding time begins at the time of collection of the last grab sample in the set . It is important that the samples be refrigerated until sampling is complete.
6.1.2 Use of Auto Samplers Use of auto samplers has virtually eliminated human error associated with manual sampling activities and significantly reduced personnel costs associated with collection of representative samples. As with any instrument, auto samplers should be checked routinely and be calibrated, cleaned, and maintained (including sample lines and bottles) according to the manufacturer's specifications.
Programming An auto sampler can be programmed to collect a variety of samples including time-composite or flow-proportional composite samples. Depending on specific equipment, the samplers can be outfitted with a single sample collection bottle or 24 individual sample bottles. Generally, automatic samplers have a purge cycle programmed into the operating system. The purge cycle is used to flush the sample collection hose prior to each individual sample collection. It is important that the function of the purge cycle be periodically checked to confirm that it is completely purging the collection system.
Cleanliness Automatic samplers can introduce contaminants to the sample. These contaminants can result from the atmosphere, lubricants, poor cleaning technique, or the materials from which the sampler is constructed. Sampler units should be checked by cycling distilled or deionized water through the
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sampler and analyzing the water for various constituents. If ambient air is used for purging cycles, the air source should be filtered to remove contaminants. All parts of the sampler, including purging chambers, pumps, and hoses, should be cleaned regularly. The frequency of cleaning depends on what is being sampled and how rapidly the unit gets dirty. Hoses should be as clean and free of collected material as possible. The manufacturer's recommended operation and maintenance procedures should be followed. When a sampler is relocated from one sampling point to another, it should be, at a minimum, cleaned thoroughly. Ideally, all hoses or parts coming in contact with the sample should be replaced. Setting up dual samplers in the same location can help identify a problem with sampling equipment.
Materials of Construction Automatic samplers used in WWTPs should be made from a durable watertight casing to protect internal components from submergence and high humidity conditions. A vandal-proof handle with a locking device is suggested. Depending on the actual location of the sampler in the WWTP, the unit may need to be manufactured to meet explosion-proof requirements. Materials of construction can vary, but it is suggested that corrosion-resistant materials such as plastics, fiberglass, and stainless steel be used.
NIREAS VOLUME 6 17 (Left)Typical portable auto sampler and (Right) autosampler unit during sampling operation from a sewer manifold
6.1.2.1 Recommended Sampling Locations for Process Control Factors that dictate where and how many samples should be collected include regulatory requirements, the size of the facility, plant performance, the intended use of the sampling data, and plant laboratory capabilities. Of course, the type and quantity of samples required on a routine basis will influence what analyses the plant laboratory should be capable of performing. The number of samples that must be taken for regulatory reporting requirements is outlined in the regulatory discharge permit. However, the specific parameter limitations listed in the permit will also influence the type and number of process control tests that need to be performed. For example, if the requirements include removal of ammonia-nitrogen, nitrogen, or phosphorus, more analyses are required at different stages of treatment to ensure that the parameter is being properly reduced. In the same manner, if the treatment plant must maintain a high degree of contaminant removal, more process control sampling and testing is required on a regular basis to maintain tighter or stricter control of the plant processes. The size of the facility and availability of laboratory staff are also factors that influence sampling program procedures. The larger and more sophisticated the treatment facility, the greater the quantity of sampling typically required and,
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therefore, the greater the number of laboratory staff needed to perform these duties. It is important to remember that all samples taken and analyzed according to proper protocol must be reported even if they are in excess of the required testing frequency. How well a plant operates without constant operational adjustment is also a factor in determining the quantity of sampling and analyses needed. A treatment plant that operates well on a continuous basis and with little operator input will require less process sampling and testing than a plant in which operational adjustments must be made constantly or one that does not historically perform well.
Waste stabilization lagoon –Samples Frequency Sampling location Analysis
Frequency
Sample type
Pond influent
BOD
Weekly
Composite
TSS
Weekly
Composite
PH
Daily
Grab
DO
Daily
Grab
pH
Daily
Grab
Temperature
Daily
Grab
BOD
Weekly
Composite
TSS
Weekiy
Composite
pH
Daily
Grab
DO
Daily
Grab
Fecnl Coliform
Daily
Grab
Chlorine Residual
Daily
Grab
Pond
Pond effluent
(WEF, 2012)
Plant influent–Samples Frequency Analysis
Frequency
Sample type
Plant Influent BOD
Daily
Composite
TSS
Daily
Composite
pH
Daily
Grab
TKN
Daily
Composite
Ammonia
Daily
Composite
Total phosphorus
Daily
Composite
(WEF, 2012)
Primary treatment –Samples Frequency
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Sampling location
Analysis
Frequency
Sample type
Primary influent
BOD
Weekly
Composite
TSS
Weekly
Composite
PH
Daily
Grab
TKN
Daily
Grab
Ammonia
Daily
Grab
Total phosphorus
Daily
Grab
BOD
Weekly
Composite
TSS
Weekly
Composite
PH
Weekly
Grab
Dissolved oxygen
Weekly
Grab
TKN0
Weekly
Composite
Total phosphorus
Weekly
Composite
Primary effluent
(WEF, 2012)
Trickling filter or rotating biological contactor plant –Samples Frequency Sampling location
Analysis
Frequency
Sample type
Influent
BOD
Daily
Composite
TSS
Daily
Composite
PH
Daily
Grab
Dissolved oxygen Daily
Grab
Dissolved oxygen Daily
Grab
PH
Daily
Grab
Temperature
Daily
Grab
Ammonia
Weekly
Composite
Nitrate
Weekly
Grab
Secondary clarifier
BOD
Daily
Composite
Effluent
TSS
Daily
Composite
Plant effluent
pH
Daily
Grab
Dissolved oxygen Daily
Grab
Ammonia
Weekly
Composite
Nitrate
Weekly
Grab
Total phosphorus
Weekly
Composite
Effluent
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Fecal coliform
Daily
Grab
Chlorine residual
Daily
Grab
(WEF, 2012)
Activated sludge –Samples Frequency Sampling location
Analysis
Frequency
Sample type
Aeration basin influent
pH
Daily
Grab
BOD
Weekly
Composite
TSS
Weekly
Composite
TKN
Monthly
Grab
Ammonia
Monthly
Grab
Alkalinity
Monthly
Grab
Dissolved oxygen
Daily
In-situ
Aeration basin
(continuous) Temperature
Daily
In-situ
(continuous) Aeration basin effluent
TSS (mixed liquor suspended Daily
Grab
solids) Settleability
Daily
Grab
pH
Weekly
Grab
Microscopic
Weekly
Grab
TSS
Daily
Grab
Flow
Daily
Totalizer
TSS
Daily
Grab
Flow
Daily
Totalizer
Secondary clarifier
Sludge blanket
Daily
In situ
Secondary clarifier effluent
BOD
Weekly
Composite
TSS
Weekly
Composite
Ammonia
Monthly
Composite
Nitrate
Monthly
Grab
Nitrite
Monthly
Grab
Total phosphorus
Monthly
Composite
PH
Daily
Grab
Turbidity
Daily
Grab
Return activated sludge
Waste activated sludge
Plant effluent
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Fecal coliform
Daily
Grab
Chlorine residual
Daily
Grab
(WEF, 2012)
Anaerobic digestion –Samples Frequency Sampling location
Analysis
Frequency
Sample type
Digester feed
Total solids
Daily
Composite
Volatile solids
Daily
Composite
pH
Daily
Grab
Alkalinity
2/Week
Grab
Temperature
Daily
Grab
PH
Daily
Grab
Volatile acids
2/Week
Grab
Alkalinity
2/Week
Grab
Total solids.
Daily
Grab
Volatile solids
Daily
Grab
Volatile acids
Weekly
Grab
TKN
Weekly
Grab
TSS
Daily
Composite
BOD
Daily
Composite
Ammonia or nitrate
Weekly
Composite
Methane
Daily
Grab
Digester contents
Digested sludge
Supernatant
Digester gas
(WEF, 2012)
Aerobic digestion–Samples Frequency Sampling location
Analysis
Frequency
Sample type
Digester feed
Total solids
Daily
Composite
Volatile solids
Daily
Composite
pH
Daily
Grab
Alkalinity
Weekly
Grab
Ammonia or nitrate
Weekly
Grab
Temperature
Daily
Grab
pH
Daily
Grab
Dissolved oxygen
Daily
Grab
Digester contents
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Total solids
Daily
Composite
Volatile solids
Daily
Composite
Ammonia or nitrate
2/ week
Grab
Alkalinity
2/week
Grab
Daily
Composite
Volatile solids
Daily
Composite
pH
Daily
Grab
Volatile acids
Weekly
Grab
Ammonia or nitrate
Weekly
Grab
TSS
Daily
Composite
BOD
Daily
Composite
Ammonia or nitrate
Weekly
Composite
Settle digested sludge Total solids
Supernatant
(WEF, 2012)
Examples of suggested sampling locations and frequencies for common WWTP processes are listed in preivous Tables. Many of the analyses listed in the tables may actually be tested more frequently based on individual plant conditions. As previously stated, the types of wastewater parameters that must be treated or removed in the plant processes will dictate what process control tests need to be performed. For example, if effluent limitations require total phosphorus removal, total phosphorus should be measured at various stages throughout the plant treatment processes. Each treatment facility is slightly different; as such, there is no one sampling and testing program that can be adapted from one facility to another without some type of modification. The person who establishes the sampling program must take into account all factors to produce a useful and meaningful sampling program.
It must be emphasized that previous Tables are just examples of suggested locations and frequencies of various samples. The operator must read and understand the discharge permit and meet sampling requirements that are dictated. Experience and a good knowledge of the biological, physical, and chemical characteristics of a specific treatment plant will aid in developing a well thought out and meaningful sampling program that will provide the facility what it needs to control the process and meet discharge permit requirements.
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6.1.3 Sampling & Testing in activated sludge process The activated sludge process generally requires more sampling and testing to maintain adequate process control than any of the other unit processes in the wastewater treatment system. During periods of operational problems, both the parameters tested and the frequency of testing may increase substantially. Process control testing may include settleability testing to determine: (1) the settled sludge volume; (2) influent and mixed liquor suspended solids; (3) return activated sludge solids and waste activated sludge concentrations; (4) volatile content of the mixed liquor suspended solids; (5) dissolved oxygen and pH of the aeration tank; and (6) BOD5 and chemical oxygen demand (COD) of the aeration tank influent and process effluent. Microscopic evaluation of the activated sludge is used to determine the predominant organism. The following sections describe most of the common process control tests.
6.1.3.1 Aeration Tank Influent and Effluent Sampling pH pH is tested daily with a sample taken from the aeration tank influent and process effluent. pH is normally close to 7.0 (normal), with the best pH range being 6.5 to 8.5 (although a pH range of 6.5 to 9.0 is satisfactory). A pH of >9.0 may indicate toxicity from an industrial waste contributor. A pH of <6.5 may indicate loss of flocculating organisms, potential toxicity, industrial waste contributors, or acid storm flow. Keep in mind that the effluent pH may be lower because of nitrification.
Temperature Temperature is important because it indicates the following: When the temperature increases ... • Organism activity increases. • Aeration efficiency decreases. • Oxygen solubility decreases. When the temperature decreases ... • Organism activity decreases. • Aeration efficiency increases. • Oxygen solubility increases.
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Dissolved Oxygen The content of dissolved oxygen (DO) in the aeration process is critical to performance. DO should be tested at least daily (peak demand). Optimum is determined for individual plants, but normal is from 1 to 3 mg/L. If the system contains too little DO, the process will become septic. If it contains too much DO, energy and money are wasted.
Settled Sludge Volume (Settleability) Settled sludge volume (SSV) is determined at specified times during sample testing. Both the 30and 60-minute observations are used for control. Subscripts (e.g., SSV30 and SSV60) indicate the settling time. The test is performed on aeration tank effluent samples.
Centrifuge Testing The centrifuge test provides a quick, relatively easy control test for the solids level in the aerator but does not usually correlate with MLSS results. Results are directly affected by variations in sludge quality.
Alkalinity Alkalinity is essential to biological activity. Nitrification requires 7.3-mg/L alkalinity per mg/L total Kjeldahl nitrogen.
BOD5 Testing showing an increase in BOD5 indicates increased organic loading; a decrease in BOD5 indicates decreased organic loading.
Total Suspended Solids
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An increase in total suspended solids (TSS) indicates an increase in organic loading; a decrease in TSS indicates a "decrease in organic loading.
Total Kjeldahl Nitrogen Total Kjeldahl nitrogen (TKN) determination is required to monitor process nitrification status and to determine alkalinity requirements.
Ammonia Nitrogen Determination of ammonia nitrogen is required to monitor process nitrification status.
Metals Metal contents are measured to determine toxicity levels.
6.1.3.2 Aeration Tank pH Normal pH range in the aeration tank is 6.5 to 9.0. Decreases in pH indicate the presence of process sidestreams or that insufficient alkalinity is available.
Dissolved Oxygen The normal range of DO in an aeration tank is 1 to 3 mg/L. Dissolved oxygen level decreases may indicate increased activity, increased temperature, increased organic loading, or decreased MLSS/MLVSS. An increase in dissolved oxygen could be indicative of decreased activity, decreased temperature, decreased organic loading, increased MLSS/ MLVSS, or influent toxicity.
Dissolved Oxygen Profile All dissolved oxygen profile readings should be >0.5 mg/L. Readings of <0.5 mg/L indicate inadequate aeration or poor mixing.
Mixed Liquor Suspended Solids The range of mixed liquor suspended solids is determined by the process modification used. When MLSS levels increase, more solids, organisms, and an older, more oxidized sludge are typical.
Microscopic Examination
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The activated sludge process cannot operate as designed without the presence of microorganisms; thus, microscopic examination of an aeration basin sample to determine the presence and type of microorganisms is important. Different species prefer different conditions; therefore, the presence of different species can indicate process conditions.
Routine process control identification can be limited to the general category of organisms present. For troubleshooting more difficult problems, a more detailed study of organism distribution may be required (the knowledge required to perform this type of detailed study is beyond the scope of this text). The major categories of organisms found in the activated sludge are: â&#x20AC;˘ Protozoa â&#x20AC;˘ Rotifers â&#x20AC;˘ Filamentous organisms
Bacteria are the most important microorganisms in the activated sludge. They perform most of the stabilization or oxidation of the organic matter and are normally present in extremely large numbers.
Protozoa Protozoa are secondary feeders in the activated sludge process (secondary as feeders but nonetheless definitely important to the activated sludge process). Their principal function is to remove (eat or crop) dispersed bacteria and help to produce a clear process effluent. To help gain an appreciation for the role of protozoa in the activated sludge process, consider the following explanation.
Rotifers Rotifers are a higher life form normally associated with clean, unpolluted waters. Significantly larger than most of the other organisms observed in activated sludge, rotifers can utilize other organisms, as well as organic matter, as their food source. Rotifers are normally the predominant organism; the effluent will usually be cloudy (pin or ash floe) and will have very low BOD5.
Filamentous Organisms
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Filamentous
organisms
(bacteria,
fungi,
etc.) occur whenever the environment of the
activated sludge favors their predominance. They are normally present in small amounts and provide the basic framework for floe formation. When the environmental conditions (e.g., pH, nutrient levels, DO) favor their development, they become the predominant organisms. When this occurs, they restrict settling, and the condition known as bulking occurs.
Note: Microscopic examination of activated sludge is a useful control tool. When attempting to identify the microscopic contents of a sample, the operator should try to identify the predominant groups of organisms.
6.1.3.3 Settling Tank Influent Dissolved Oxygen The dissolved oxygen level of the activated sludge settling tank should be 1 to 3 mg/L; lower levels may result in rising sludge.
pH Normal pH range in an activated sludge settling tank should be maintained between 6.5 and 9.0; decreases in pH may indicate alkalinity deficiency.
Alkalinity A lack of alkalinity in an activated sludge settling tank will prevent nitrification.
Total Suspended Solids Mixed liquor suspended solids sampling and testing are required for determining solids loading, mass balance, and return rates.
Settled Sludge Volume (Settleability) Settled sludge volume (SSV) is determined at specified times during sample testing (e.g., 30- and 60-minute observations). • Normal operation—When the process is operating properly, the solids will settle as a blanket (a mass), with a crisp or sharp edge between the solids and the liquor above. The liquid over the solids will be clear, with little or no visible solids remaining in suspension. Settled sludge volume at the end of 30 to 60 minutes will be in the range of 400 to 700 mL. • Old or overoxidized activated sludge—When the activated sludge is overoxidized, the solids will settle as discrete particles. The edge between the solids and liquid will be fuzzy, with a large
NIREAS VOLUME 6 28
number of visible solids (e.g., pin floe, ash floe) in the liquid. The settled sludge volume at the end of 30 or 60 minutes will be greater than 700 mL. • Young or underoxidized activated sludge—When the activated sludge is underoxidized, the solids settle as discrete particles, and the boundary between the solids and the liquid is poorly defined. Large amounts of small visible solids are suspended in the liquid. The settled sludge volume after 30 to 60 minutes will usually be less than 400 mL. • Bulking activated sludge—When the activated sludge is experiencing a bulking condition, very little or no settling is observed.
Note: Running the settleability test with a diluted sample can assist in determining if the activated sludge is old (too many solids) or bulking (not settling). Old sludge will settle to a more compact level when diluted.
Flow Monitoring flow in settling tank influent is important for determination of the mass balance.
Jar Tests Jar tests are performed as required on settling tank influent and are beneficial in determining the best flocculant aid and appropriate doses to improve solids capture during periods of poor settling.
6.1.3.4 Settling Tank Sludge Blanket Depth Sludge blanket depth refers to the distance from the surface of the liquid to the solids-liquid interface or the thickness of the sludge blanket as measured from the bottom of the tank to the solids-liquid interface. Part of the operator's sampling routine, this measurement is taken directly in the final clarifier. Sludge blanket depth is dependent on hydraulic load, return rate, clarifier design, waste rate, sludge characteristics, and temperature. If all of the other factors remain constant, the blanket depth will vary with amount of solids in the system and the return rate; thus, it will vary throughout the day. Note: The depth of the sludge blanket provides an indication of sludge quality; it is used as a trend indicator. Many factors can affect the test result.
Suspended Solids and Volatile Suspended Solids
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Suspended solids and volatile suspended solids concentrations of the mixed liquor suspended solids (MLSS), the return activated sludge (RAS), and waste activated sludge (WAS) are routinely sampled and tested because they are critical to process control.
6.1.3.5 Settling Tank Effluent BOD5 and Total Suspended Solids Testing for BOD5 and total suspended solids is conducted variably (daily, weekly, or monthly). Increases indicate that treatment performance is decreasing; decreases indicate that treatment performance is increasing.
Total Kjeldahl Nitrogen Total Kjeldahl nitrogen (TKN) sampling and testing are variable. An increase in TKN indicates that nitrification is decreasing; a decrease in TKN indicates that nitrification is increasing.
Nitrate Nitrogen Nitrate nitrogen sampling and testing are variable. Increases in nitrate nitrogen indicate increasing nitrification or an industrial contribution of nitrates. A decrease indicates reduced nitrification.
Flow Settling tank effluent flow is sampled and tested daily. Results are required for several process control calculations.
6.1.3.6 Return Activated Sludge and Waste Activated Sludge Total Suspended Solids and Volatile Suspended Solids Total suspended solids and total volatile suspended solids concentrations of the mixed liquor suspended solids, return activated sludge, and waste activated sludge are routinely sampled (using either grab or composite samples) and tested, because they are critical to process control. The results of the suspended and volatile suspended tests can be used directly or to calculate such process control figures as mean cell residence time (MCRT) or food-to-microorganisms (F/M) ratio. In most situations, increasing the MLSS produces an older, denser sludge, and decreasing MLSS produces a younger, less dense sludge.
Note: Control of the sludge wasting rate by maintaining a constant MLVSS concentration requires maintaining a certain concentration of volatile suspended solids in the aeration tank.
NIREAS VOLUME 6 30 Flow The flow of return activated sludge is tested daily. Test results are required to determine the mass balance and for control of the sludge blanket, MLSS, and MLVSS. For waste activated sludge, flow is sampled and tested whenever sludge is wasted. Results are required to determine mass balance and to control solids level in process.
Process Control Adjustments In the routine performance of their duties, wastewater operators make process control adjustments to various unit processes, including the activated sludge process. Following is a summary of the process controls available for the activated sludge process..
Process Control: Return Rate Condition: Return rate is too high. Result: • Hydraulic overloading of aeration and settling tanks • Reduced aeration time • Reduced settling time • Loss of solids over time Condition: Return rate is too low. Result: • Septic return • Solids buildup in settling tank • Reduced MLSS in aeration tank • Loss of solids over weir
Process Control: Waste Rate Condition: Waste rate is too high. Result: • Reduced MLSS • Decreased sludge density • Increased SVI • Decreased MCRT • Increased F/M ratio Condition: Waste rate is too low.
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Result: • Increased MLSS • Increased sludge density • Decreased SVI • Increased MCRT • Decreased F/M ratio
Process Control: Aeration Rate Condition: Aeration rate is too high. Result: • Wasted energy • increased operating cost • Rising solids • Breakup of activated sludge Condition: Aeration rate is too low. Result: • Septic aeration tank • Poor performance • Loss of nitrification
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6.2 Design, Infrastructure and Management
6.2.1 Laboratory services Quality control of water and wastewater laboratory analyses involves consideration and control of the many variables that affect the production of reliable data. The quality of the laboratory services available to the analyst must be included among these variables. An abundant supply of distilled water, free from interferences and other undesirable contaminants, is an absolute necessity. An adequate source of clean, dry, compressed air is needed. Electrical power for routine laboratory use and voltage-regulated sources for delicate electronic instrumentation must be provided.
NIREAS VOLUME 6 33 6.2.1.1 Distilled Water Distilled or demineralized water is used in the laboratory for dilution, preparation of reagent solutions, and final rinsing of glassware. Ordinary distilled water is usually not pure. It may be contaminated by dissolved gases and by materials leached from the container in which it has been stored. Volatile organics distilled over from the feed water may be present, and nonvolatile impurities may occasionally be carried over by the steam, in the form of a spray. The concentration of these contaminants is usually quite small, and distilled water is used for many analyses without further purification. However, it is highly important that the still, storage tank, and any associated piping be carefully selected, installed, and maintained in such a way as to insure minimum contamination. Water purity has been defined in many different ways, but one generally accepted definition states that high-purity water is water that has been distilled or deionized, or both, so that it will have a specific resistance of 500,000 Ω or greater (or a conductivity less than 2.0 μmho/cm). This definition is satisfactory as a base to work from, but for more critical requirements, the breakdown shown in next table has been suggested to express degrees of purity.
Water purity
(US EPA, 1979)
Type I grade water is prepared by the distillation of feed water having a maximum conductivity of 20 μmho/cm at 25°C followed by polishing with a mixed bed of ion exchange materials and a 0.2μm membrane filter. Type ΙΙ grade water is prepared by using a still designed to produce a distillate having a conductivity of less than 1.0 μmho/cm at 25°C. This may be accomplished by double distillation or the use of a still incorporating special baffling and degassing features.
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Type III grade water is prepared by distillation, ion exchange, or reverse osmosis, followed by polishing with the 0.45-Îźm membrane filter.
Type IV grade water is prepared by distillation, ion exchange, reverse osmosis, or electrodialysis.
6.2.1.2 Ammonia free Water Removal of ammonia can be accomplished by shaking ordinary distilled water with a strong cation exchanger, or by passing distilled water through a column of such material.
6.2.1.3 Carbon-Dioxide-FreeWater Carbon-dioxide-free water may be prepared by boiling distilled water for 15 min and cooling to room temperature. As an alternative, distilled water may be vigorously aerated with a stream of inert gas for a period sufficient to achieve saturation and CO2 removal. Nitrogen is most frequently used. The final pH of the water should lie between 6.2 and 7.2. It is not advisable to store CO2-free water for extended periods.
6.2.1.4 Ion-FreeWater A multipurpose high purity water, free from trace amounts of the common ions, may be conveniently prepared by slowly passing distilled water through an ion-exchange column containing one part of a strongly acidic cation-exchange resin in the hydroxyl form. Resins of a quality suitable for analytical work must be used. Ion-exchange cartridges of the research grade, available from scientific supply houses, have been found satisfactory. By using a fresh column and high-quality distilled water, a water corresponding to the ASTM designation for type I reagent water (2) (maximum 0.1 mg/l of total matter and maximum conductivity of 0.06 mho/cm) can be obtained. This water is suitable for use in the determination of ammonia, trace metals, and low concentrations of most cations and anions. It is not suited to some organic analyses, however, because this treatment adds organic contaminants to the water by contact with the ion-exchange materials.
NIREAS VOLUME 6 35
Typical ion-exchange column for the production of ion-freewater
6.2.1.5 Compressed Air The quality of compressed air required in the laboratory is usually very high, and special attention should be given to producing and maintaining clean air until it reaches the outlet. Oil, water, and dirt are undesirable contaminants in compressed air, and it is important to install equipment that generates dry, oil-free air. When pressures of less than 50 psi are required, a rotary-type compressor, using a water seal and no oil, eliminates any addition of oil that would subsequently have to be removed from the system. Large, horizontal, water-cooled compressors will usually be used when higher pressures are required. Compression heats air, thus increasing its tendency to retain moisture. An aftercooler is therefore necessary to remove water. Absorption filters should be used at the compressor to prevent moisture from entering the piping system. Galvanized steel pipe with threaded, malleable-iron fittings, or solder-joint copper tubing should be used for piping the air to the laboratory. When the compressed air entering the-laboratory is of low quality, an efficient filter should be installed between the outlet and the point of use to trap oil, moisture, and other contaminants. As an alternative, high-quality compressed air of the dry grade is commercially available in cylinders when no other source exists.
NIREAS VOLUME 6 36
6.2.1.6 Vacuum A source of vacuum in the chemical laboratory, is a very useful item. While used primarily as an aid in filtration, it is also sometimes used in pipetting and in speeding up the drying of pipets.
6.2.1.7 Hood System An efficient hood system is a requirement for all laboratories. In addition to removing the various toxic and hazardous fumes that may be generated when using organic solvents, or that may be formed during an acid digestion step, a hood system may also be used to remove toxic gases that may be formed during atomic absorption analyses or other reactions. A regular fume hood should have a face velocity of 40 m/min (linear) with the sash fully open.
NIREAS VOLUME 6 37
6.2.1.8 Electrical Services An adequate electrical system is indispensable to the modern laboratory. This involves having both 115- and 230-V sources in sufficient capacity for the type of work that must be done. Requirements for satisfactory lighting, proper functioning of sensitive instruments, and operation of high-current devices must be considered. Any specialized equipment may present unusual demands on the electrical supply. Such instruments as spectrophotometers, flame photometers, atomic absorption equipment, emission spectrographs, and gas chromatographs have complicated electronic circuits that require relatively constant voltage to maintain stable, drift-free instrument operation. If the voltage of these circuits varies, there is a resulting change in resistance, temperature, current, efficiency, light output, and component life. These characteristics are interrelated, and one cannot be changed without affecting the others. Voltage regulation is therefore necessary to eliminate these conditions. Electrical heating devices provide desirable heat sources, and should offer continuously variable temperature control. Hot plates and muffle furnaces wired for 230-V current will probably give better service than those that operate on 115 V, especially if the lower voltage circuit is only marginally adequate. Water baths and laboratory ovens with maximum operating temperatures of about 200째C perform well at 115 V. Care must be taken to ground all equipment that could constitute a shock hazard. The three-pronged plugs that incorporate grounds are best for this purpose.
6.2.1.9 Lighting Because of the special type of work, requirements for a laboratory lighting system are quite different from those in other areas. Accurate readings of glassware graduations, balance vemiers, and other measuring lines must be made. Titration endpoints, sometimes involving subtle changes in color or shading, must be observed. Levels of illumination, brightness, glare, and location of light sources should be controlled to facilitate ease in making these measurements and to provide maximum comfort for the employees. Minimum lighting level for a laboratory is considered to have a value of no less than 750 Lux, with natural characteristics.
NIREAS VOLUME 6 38
6.2.2 Housekeeping 6.2.2.1 Laboratory Environment The most important area affecting the contamination of samples is the sample preparation environment. The ability to control the environment within the laboratory is extremely important to ensure sample integrity. The operator-analyst should maintain a separate, identifiable area for laboratory procedures. Preferably, the laboratory site should be located away from sources of mechanical vibration, shock, and electrical interference. The noise level should not exceed that of a quiet office.
6.2.2.2 Climate The work area of a laboratory should be free from excessive drafts and the temperature should be kept reasonably stable, with a standard temperature of 20 ¹ 2 °C. Generally, the relative humidity should not exceed 55%. The laboratory should be sensibly, but not clinically, dust-free. Walls, floors, and ceilings should be of a finish that will not make or collect dust. For example, untreated concrete floors or ceilings with excessive loose particles are unsuitable. Lastly, proper lighting is crucial for proper sample handling.
6.2.2.3 General Cleanliness The operator is responsible for keeping the laboratory clean. The bench top or work area should always be cleaned after use and equipment should be washed and dried and returned to its proper storage place. Used paper towels and Kimwipes should be thrown away, and chemicals and laboratory materials should be put away immediately when finished. Cabinet doors should be kept closed to prevent dust from settling on stored laboratory equipment. The operator should try to isolate the laboratory from the plant by keeping doors closed. It is important to never eat, drink, smoke, chew gum, or apply cosmetics in sample preparation areas or areas where laboratory chemicals are present. The operator should always wash hands before and after performing any laboratory procedure. Keeping the work area clean and uncluttered will significantly minimize the potential for contamination.
6.2.2.4 Washing Dishes Washing laboratory dishes (laboratory equipment) may be the most mundane task in a WWTP; however, improper handling of sample containers, glassware, and other apparatuses can lead to faulty and imprecise results. Development and adherence to a standard operating procedure for cleaning laboratory equipment may be the single most important method of reducing sample contamination. Sources of contamination to be aware of include contaminated sample containers, unclean glassware and filters, use of cleaning products inappropriate for the proposed analysis,
NIREAS VOLUME 6 39
and inadequate rinsing of glassware during the cleaning process. The longer chemicals and reagents stand in glassware, the more chance they have to adhere to the walls of the glass and the more difficult it becomes to get them thoroughly clean. The operator should adopt the concept of "clean as you go" as opposed to "clean before you go". Indeed, a wash station should be set up daily so that it is convenient to wash glassware immediately after use.
The following are general instructions on how to wash common WWTP laboratory equipment. Special consideration should be given to each test performed. For example, nitrogen- or phosphorus-free laboratory-grade detergents are available and should be used with the corresponding containers and glassware. Many analyses have specific instructions for sample bottle preparation. Additionally, if a contract laboratory is being used, sample bottles are provided in accordance with Standard methods guidelines. If a laboratory-specific dishwasher is being used, any tape or numbering on the glassware should be removed using a solvent such as acetone. Laboratory equipment should be placed in a dishwasher immediately after use. The washer is designed to thoroughly clean all laboratory glassware and accessories and is preprogrammed for glassware washing. The operator should check the owner's manual for the appropriate glassware setting. For laboratory equipment that is too large for an automatic dishwasher or that cannot be feasibly washed in an automatic dishwasher (i.e., volumetric flasks), hand washing is required. Again, any tape, numbers, and so on from sample bottles should be removed. Laboratory equipment should be immersed in a solution of laboratory-appropriate synthetic detergent such as Liquinox or Alconox (Alconox, Inc., White Plains, New York; available through laboratory supply companies). Glassware should be scrubbed with a soft-bristle brush to loosen any adhered particles, triple rinsed with tap water to remove visible detergent, triple rinsed with distilled or deionized water (if available), and then allowed to drip dry inverted. Laboratory equipment should be returned to the appropriate cabinet or drawer. For microbiology sample containers (i.e., Escherichia coli and fecals), after the aforementioned washing procedure, designated bottles are sterilized by auto-claving. An autoclave manufacturer's specifications should be followed for sterilization time. Filtering apparatuses should be wrapped in autoclavable paper and taped with heat sensitive tape prior to autoclaving. Autoclavable bottles should be autoclaved with lids loosely in place and taped with heat sensitive tape. The heat sensitive tape ensures that the proper temperature was reached for sterilization.
6.2.2.5 Acid Washes For glassware requiring acid washing (i.e., phosphorus sample collection bottles, BOD bottles, and trace metals), the operator should follow the general washing procedure and then immerse bottles in a 10% hydrochloric acid solution or 10% nitric acid solution for trace metals (1 part acid to 9
NIREAS VOLUME 6 40
parts water). The acid wash should be prepared by slowly pouring and stirring the acid into the water. The bottles should be soaked a minimum of 1 hour (preferably overnight), triple-rinsed with distilled or deionized water, and allowed to drip dry inverted. Glassware should be returned to the appropriate cabinet or drawer. It is important to note that extreme care is needed when working with acids. Proper ventilation, goggles, and protective clothing are necessary. The acid bath should be contained with a suitable cover for safety. For acid wash disposal, the acid wash should be neutralized with a saturated solution of sodium carbonate (soda ash) or other basic solution. The operator should slowly add soda ash or another basic solution into the diluted acid while stirring. The operator should monitor pH with a pH meter, pH indicator strips, or other pH test method. When the pH is between 6 and 9, the solution should be disposed of in the sink drain and drain should be flushed with excess water. A neutral pH is preferable to lessen the risk of plumbing damage.
6.2.2.6 Oxidizers Specialty cleaning solutions clean glass vigorously by oxidizing the surface. This process is necessary for extremely soiled glassware. Chromic acid is the standard method for cleaning BOD bottles . If chromic acid is retained on any residual grease layers, it will interfere with bacterial growth. Additionally, the operator should be aware that chromium is highly toxic and requires special disposal following the MSDS protocol.
6.2.3 Historical Records A database of historical sampling and analyses is invaluable to operators and engineers. For'the operator, a historical database can show seasonal variations at the treatment plant, pointing out past abnormal conditions that can help in preparing for treatment process adjustments. A historical database can also point to corrective actions used in the past for recurring abnormal conditions; in other words, it can reveal which corrective actions have worked and which have not.
Unless facts associated with sample collection, preservation, and handling are recorded carefully, all test results from a particular analysis may be irrelevant. The laboratory has the responsibility to prove that given test results are from the given sample and that appropriate methods and procedures were used to obtain the results. Therefore, recordkeeping and proper reporting are as important as the actual analysis itself. The first requirement for meaningful data is that a sample be representative and carefully handled before analysis begins. The analyst must then complete proper analysis in the prescribed fashion, record all associated facts and figures, and report the given data in the proper form. The proper way to record and report data is presented in this chapter.
NIREAS VOLUME 6 41 6.2.3.1 Benchsheets Each plant has different needs for collecting and recording data; there are no standard laboratory forms. Most treatment plants develop worksheets for recording laboratory results; these are typically referred to as benchsheets. The benchsheet satisfies the followingtwo requirements: (1) it provides a record of the data and (2) it arranges the information in an orderly manner. Writing laboratory results on scraps of paper may result in important process control information being inadvertently thrown away, misplaced, or otherwise rendered unreadable. Benchsheets for laboratory analysis provide a single uniform location to document work that was performed and make it easy to record, review, and recover data when completing forms.
The first laboratory benchsheet that must be maintained is the sample log. This log documents when the sample was collected, from where it was collected, who collected the sample, how it was preserved, the analysis that needs to be run, and a column for recording abnormal conditions. Any departure from standard sampling protocol must be noted in the sample log. The most common types of benchsheets are those used for analysis documentation of work performed on the samples. At a minimum, this includes:
• Analysts initials, • Date and time of analysis, • Sample date(s), • Sample name or identification, • Preparation date or identification (if generated) of stock solutions, • Preparation date of identification (if generated) of standards, • Preparation date of buffering solutions, • Method reference, • Instrument and electrode model and serial number, • Location of analysis being performed, and • Batch number for reporting results in the data system. 6.2.3.2 Log Book Typically, records of all data should be kept for 5 years from the date of the sample, measurement, report, or application. The actual date is set through the regulatory process. This information includes:
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• The date, exact place, and time of sampling or measurements; • The individual(s) who performed the sampling or measurements; 0 The laboratory that performed the analyses; • The date(s) analyses was performed; • The individual(s) who performed the analyses; • The analytical techniques or methods used, including any modifications; • The results of such analyses, including: - Units of measurement; - Minimum reporting limit for the analysis; - Results less than the reporting limit but above the method detection limit (MDL); - Data qualifiers and a description of the qualifiers; - Quality control test results (and a written copy of the laboratory quality assurance plan); - Dilution factors, if used; and - Sample matrix type; and • Electronic data and information regarding influent and effluent flow, pH, and other constituents subject to monitoring or effluent limitations generated by the Supervisory Control and Data Acquisition system.
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6.3 Laboratory basics 6.3.1 Measures of Precision 6.3.1.1 Mean When analyzing the precision of a group of results, the operator-analyst should be concerned with how they are distributed around the mean, or average, of the results. The mean is simply the sum of all results divided by the number of results, as follows:
Mean =
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6.3.1.3 Standard Deviation If all the errors in a test are random, the results will most likely follow a normal distribution where there are the same number of high and low results and these results have roughly the same RPD (higher or lower) from the mean. In this instance, the standard deviation (SD) can provide the measure of precision, as follows (a low standard deviation indicates high precision):
SD =
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6.3.1.4 Relative Standard Deviation The relative standard deviation (RSD) allows for precision comparisons between high and low analyte concentrations. It is found by dividing standard deviation by the mean. When expressed as
% RSD =
a percentage (%RSD), it is also known as the coeffiecient of variation.
RSD =
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6.3.3 Quality assurance and quality control 6.3.3.1 Quality Assurance System Without quality control results, there can be no confidence in the results of analytical tests. Essential quality control measures include method calibration, reagent standardization, assessment of each analyst's capabilities, analysis of blind check samples, determination of the method's sensitivity (method detection level or quantification limit), and daily evaluation of bias, precision, and the presence of laboratory contamination or other analytical interference. Details of these procedures, their performance frequency, and expected ranges of results should be formalized in a written quality assurance manual and standard operating procedures. Some of the methods an operator-analyst will use include specific quality control procedures, frequencies, and acceptance criteria. These are considered to be the minimum quality controls needed to perform the method successfully. Additional quality control procedures can and should be used. Some regulatory programs may require additional quality control or have alternative acceptance limits. Each method typically includes acceptance criteria guidance for precision and bias of test results. If not, the laboratory should determine its own criteria via control-charting techniques. For some procedures, including pH, dissolved oxygen, residual chlorine, and carbon dioxide, the traditional determination of bias (i.e., adding a known amount of analyte to either a sample or a blank) is not possible. This does not, however, relieve analysts of the responsibility for evaluating test bias. Instead, certified ready-made analyte solutions should be obtained for such tests. Precision should be evaluated by analyzing duplicate samples. If one or both results are "nondetect", however, precision cannot be calculated. To help verify the accuracy of calibration standards and overall method performance, the operatoranalyst should participate in an annual or, preferably, semiannual program of analysis of known quality control quality check samples (QCSs) that are ideally provided by an external agency. Such programs are sometimes called proficiency testing or performance evaluation studies. An unacceptable result on a proficiency testing sample is often the first indication that a test protocol is not being followed successfully. The operator-analyst should investigate circumstances fully to find the cause. In many jurisdictions, participation in proficiency testing studies is a required part of laboratory certification and accreditation.
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6.3.4 Elements of quality control A variety of quality control analyses are completed regularly in a laboratory. Characteristically, an acceptable result is obtained for each quality control check before measurement of samples begins. Each check is periodically repeated, validating the analyses of intervening samples. Corrective steps are performed if the check fails, and the intervening samples are remeasured. The frequency of quality control checks varies. A sample set or batch is considered to be 20 samples.
6.3.4.1 Method Blank A method blank (also called a reagent blank) is a volume of reagent water treated exactly as a sample, including exposure to all equipment, glassware, procedures, reagents, and preservatives. The method blank is used to assess whether analytes or interferences are present in the analytical process. Any constituent(s) recovered must be less than or equal to one-half the reporting level (unless the method specifies otherwise). If any method blank measurements are at or above the reporting level, immediate corrective action should be taken. At least one method blank should be included daily or with each batch of 20 or fewer samples.
6.3.4.2 Laboratory-Fortified Blank A laboratory-fortified blank (LFB) (also called a blank spike) is a method blank that has been fortified with a known concentration of analyte from a second source (not the one used to develop working standards, unless the method specifies otherwise). The LFB is used to evaluate accuracy, ongoing laboratory performance, and analyte recovery in a clean matrix.
NIREAS VOLUME 6 48 Frequency of quality control checks Quality control element
Frequency
Method blank
One per sample set or 5% basis, whichever is more frequent
Laboratory fortified blank
One per sample set or 5% basis, whichever is more frequent
Laboratory fortified matrix
One per sample set or 5% basis, whichever is more frequent
Duplicates
One per sample set or 5% basis, whichever is more frequent
Calibration
One per analysis
Continued calibration verification
One per sample set then 1 every 10 samples following
Quality control sample
Quarterly
Using stock solutions prepared with the second source, fortified concentrations should be prepared so they are at or below the midpoint of the calibration curve. Ideally, LFB concentrations should be varied to cover the entire midpoint and lower part of calibration curve, including the reporting limit. The operator-analyst should ensure that LFB meets the method's performance criteria when such criteria are specified. Corrective actions to be taken if the LFB does not satisfy acceptance criteria should be established.At least one LFB should be included daily or per each batch of 20 or fewer samples. If the method's sample results typically will be "nondetect", the operator-analyst should consider using duplicate LFBs to assess precision.
6.3.4.3 Duplicates Duplicate samples of measurable concentration should be used to measure the analytical process'precision. Routine samples to be analyzed twice should be randomly selected. Duplicate samples should be processed independently through the entire sample preparation and analysis. At least one duplicate for each matrix type should be included daily or with each batch of 20 or fewer samples. Control limits for duplicates should be calculated when method-specific limits are not provided.
6.3.4.4 Calibration Initial calibration should lake place with at least one blank and three calibration standards of the analyte(s) of interest. Calibration standards should be selected that bracket the sample's expected concentration and are within the method's operational range. The number of calibration points depends on the width of the operational range and the shape of the calibration curve. One calibration standard should be at or below the method's reporting limit.
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As a general rule, differences among calibration standard concentrations should not be greater than 1 order of magnitude (i.e., 1, 10, 100, and 1000). However, most methods for inorganic nonmetals do not have wide operational ranges so the concentrations in their initial calibration standards should be less than 1 order of magnitude apart. Linear or polynomial curve-fitting statistics should be applied, as appropriate, to analyze the calibration curve. In most instances, a linear regression analysis will be sufficient for the operator-analyst. The appropriate linear or nonlinear correlation coefficient (R2) for standard concentration to instrument response should be greater than or equal to 0.995. Initial calibration should be used to quantify analyte concentrations in samples. Calibration verification should only be used to check initial calibration and not to quantify samples. Initial calibration should be repeated daily or when starting a new batch of samples, unless the method permits calibration verification between batches.
6.3.4.5 Continuing Calibration Verification Continuing calibration verification (CCV) is the periodic confirmation that instrument response has not changed significantly since initial calibration. Calibration can be verified by periodically analyzing a calibration standard and calibration blank during a run (typically, after each batch of 10 samples and at the end of a sample run). The CCV standard's analyte concentration should be at the midpoint of the calibration curve or lower. For calibration verification to be valid, standard results must not exceed Âą10% of its true value and calibration blank results must not be greater than one-half the reporting level (unless the method specifies otherwise). If a calibration verification fails, the operator-analyst should immediately cease analyzing samples and initiate corrective action. Then, initial calibration should be repeated and samples run since the last acceptable calibration verification should be reanalyzed.
6.3.4.6 Initial Demonstration of Capability Before a new analyst runs any samples, his or her capability should be verified. A laboratory fortified blank (LFB) should be run at least four times and compared to the limits listed in the method. This process should be repeated after analyzing at least 20 batches of samples to demonstrate proficiency with the method. If no limit is specified, the LFB's recovery limits should be set at the mean Âą (4.54 X standard deviation). In addition, the operator-analyst should verify that the method is sensitive enough to meet measurement objectives for detection and quantitation by determining the lower limit of the operational range.
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6.3.4.7 Quality Control Sample An externally generated, blind QCS (unknown concentration) should be analyzed at least annually (preferably, semiannually or quarterly). This sample should be obtained from a source external to the laboratory and the results compared to that laboratory's acceptance results. If testing results do not pass acceptance criteria, the operator-analyst should investigate why, take corrective action, and analyze a new QCS. This process should be repeated until results meet acceptance criteria.
6.3.4.8 Control Charts Control charts plot the results of quality control analyses vs time and allow the analyst to see if a method is in control or tending to bias. A simple accuracy control chart plots the percent recovery of an LFB or LFM analysis against the date, as shown in next Figure. A measure of precision, such as RPD, between duplicates can be plotted on a control chart in a similar way. The data in Figure are randomly distributed around 100%, indicating that the error responsible for the distribution is random error. If the control chart reveals that a quality control parameter is consistently high or low, it is evidence of a systematic error in the method or analysis and the analyst should look to correct this error. Warning limits are also commonly established in addition to the upper and lower control limits shown in next Figure. The analyst must decide where to set all these limits. Control charts can be constructed in many ways and become complex and specific to the individual laboratory. The operator-analyst should refer to Standard Methods for guidance on control charts and setting warning and control limits.
NIREAS VOLUME 6 51 Simple control chart for percent recovery
(WEF, 2012)
6.3.5 Limits and Levels 6.3.5.1 Instrument Detection Limit Most analytical instruments produce a signal even when a blank is analyzed (i.e., the noise level) S. The instrument detection limit (IDL) is a measure of the relative strength of analytical signal to the average strength of the background instrument noise. This ratio is useful for determining the effect of the noise on the relative error of a measurement. The strength to noise ratio can be measured many ways. One way to approximate the ratio is by dividing the arithmetic mean (average) of a series of replicates (preferably 8) by the standard deviation of the replicate results.
6.3.5.2 Method Detection Level The method detection level (MDL) is the concentration at which it is 99% probable that the sample will produce an instrument signal that is greater than the blank. The MDL is calculated from the standard deviation of seven replicate LFBs or LFMs analyzed over 3 to 5 days. Because the samples are carried through the entire method, the MDL is specific to method and analyst. There is much and varied guidance on determining the concentration of spike to use for determining an
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MDL. First, an estimate of MDL must be made. The operator-analyst should first look to Standard Methods for a given MDL for a specific method. If this is not available, IDL information should be obtained from the instrument manufacturer and the MDL should be estimated as 4 times the IDL. Once the MDL estimate is determined, the following procedure can be used:
(1) Make a LFB in the range of 2 to 5 times the MDL; (2) Analyze the LFB through the entire method; 3) Record results; and (4) -Repeat steps 1 through 3 seven times over 3 to 5 days. For example, run two samples on day 1, three on day 2, and two on day 3. Use the same source to make the LFB each day.
The mean standard deviation should be calculated as follows:
SD =
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6.3.5.3 Quantitation Limits A quantitation limit is the lowest concentration of an analyte that can be consistently measured within specific limits of precision, accuracy, representativeness, completeness, and comparability during routine laboratory operating conditions. Factors influencing the quantitation limit include sample size, analytical instrument, method, and analytical uncertainties in the sample matrix. For example, a quantitation limit may be lower for an analyte when analyzing a drinking water sample vs a wastewater sample because of the matrix of each. Quantitation limits come in many varieties, such as minimum quantitation limit, practical quantitation limit, and lower quantitation limit; these are defined differently by different laboratories, but typically fall in the range of 5 to 10 times the MDL.
6.3.5.4 Reporting Limits Reporting limits are even more abstract than quantitation limits.. Reporting limits can be set by laboratory staff according to what they feel comfortable reporting in a legal framework. They can also be specified by a client when using a contract laboratory. Many states have guidance on reporting limits regarding discharge monitoring reports.
6.3.5.5 Expression of results Generally, the chemical and physical results are expressed in milligrams per liter (mg/L) or parts per million (ppm). If concentrations are less than 0.1 mg/L, it may be more convenient to express results in micrograms per liter (Îźg/L). If concentrations are more than 10 000 mg/L, results should be expressed as percent (%); 10 000 mg/L equals 1% when the specific gravity is one. The following equations can be used to convert the results from slurries like sludge samples or solids samples to parts per million or percent by mass:
Definitions Proper use of significant figures indicates the reliability of the chosen analytical method and eliminates ambiguity in reporting. A number expresses quantity; a figure is any of the characters 0,1,2,3,4,5,6,7,8, and 9 which, alone or in combination, express a number. Reported values should contain only significant figures. A value is made up of significant figures when it contains all digits
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known to be true and one last digit in doubt. For example, if a value is reported as 12.2 mg/L, the "12" must be a firm value while the "0.2" is somewhat uncertain and may be "0.1" or "0.3".
The digit, zero (0), may or may not be a significant figure as the following instances illustrate:
• Final zeros after a decimal point are always significant figures. For example, 2.34 g to the nearest milligram is reported as 2.300 g. • Zeros before a decimal point with other preceding digits are significant. If there is no other preceding digit, a zero before the decimal point is not significant. • If there are no digits preceding a decimal point, the zeros that appear after the decimal point but precede the other digits are not significant. These zeros only indicate the position of the decimal point. • Final zeros in a whole number may or may not be significant. A good measure of significance of one or more zeros before or after another digit is to determine whether the zeros can be dropped by expressing the number in exponential form. If they can, the zeros are not significant. For example, no zeros can be dropped when expressing a mass of 100.02 g in exponential form; therefore, the zeros are significant. However, a mass of 0.002 g can be expressed hi exponential form as 2 Χ 10-3 g, and the zeros are not significant.
Rounding Off Numbers To round off numbers, drop those digits that are not significant. If the digit 6, 7, 8, or 9 is dropped, increase the preceding digit by one unit. For example, 5.48 is rounded off to 5.5. If the digit 0, 1, 2, 3, or 4 is dropped, do not alter the preceding digit. For example, 5.43 is rounded off to 5.4. If the digit 5 is dropped, round off the preceding digit to the nearest even number. For example, 5.35 is rounded off to 5.4, and 5.45 is rounded off to 5.4.
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6.3.6 Basic chemistry 6.3.6.1 Using the Periodic Table of the Elements The periodic table is the foundation of basic chemistry and provides information about elements that is useful in determining concentrations of solutions. The name, symbol, atomic number, atomic weight, and most common oxidation state, or valence, are generally given. The periodic chart should have a legend on it. The chemical symbol is a one- or two-letter abbreviation of the chemical name and is useful shorthand when combining elements into chemical compounds. The atomic number is the number of protons, or positively charged particles, in the nucleus of the atom. The atomic weight of an element is the weight in grams of 1 mol (grams per mole [g/mol]) of the element. Atomic weight is the most important piece of information to the operational chemist because it is the basis for determining the concentration of chemicals in a solution. The oxidation state indicates the charge of the element.
6.3.6.2 Moles It is also important to understand the concept of the mole. A mole is simply a measure of the number of items or particles. In the same way that a pair is 2, a quartet is 4, or a dozen is 12, a mole is 6.022 Χ 1023 particles or, in this instance, atoms or molecules. The number assigned to the mole, 6.022 Χ 1023, is known as Avogadro's number. The atomic weight of an element is the weight in grams of 1 mol of the element; therefore, a larger, heavier element (higher atomic number) will have a larger atomic weight. In calculations, atomic and molecular weight should be expressed in grams per mole.
6.3.6.3 Chemical Compounds Elements combine to form compounds by sharing electrons to achieve a neutral charge. In our example, calcium and chlorine combine to form calcium chloride. The periodic table gives the needed information to predict how these elements will react with each other. Because calcium has a 2+ charge and chlorine has a single negative charge, the reaction results in a zero charge for the product molecule, as evidenced in the following chemical equation: 1mol)Ca2+ + 2(mol)Cl- ď&#x192; 1(mol)CaCl2
6.3.6.4 Formula Weight The formula weight, also called the molar mass of a chemical compound, is the sum of the atomic weights, as illustrated in next Table. It is important to note that the number of moles do not add
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together; rather, 1 mol of calcium chloride contains 1 mol of calcium and 2 mol of chloride. The lowest number of moles on the left side of the chemical equation limits the number of moles on the right; as such, if one were to react 2 mol of calcium with 4 mol of chloride, 2 mol of calcium chloride would be produced.
Periodic table representation of calcium and chloride
Calculating formula weight. Element
Atomic weight, g/mol Quantity, mol
Ca
40.08
X1
= 40.08
CI
35.45
X2
= 70.90
1
= 110.98
Formula weight g/mol (WEF, 2012)
6.3.6.5 Molar Solutions The concentration of a chemical in a solution is often given in molarity (M). Molarity refers to the number of moles of chemical per liter of solution (mol/L). The formula weight can be used as a conversion factor to make a molar solution. For 1 Î&#x153; calcium chloride (CaCL2), 1 mol CaCl2/L x 110.98 g/mol = 110.98 g/L To make this solution, 110.98 g of calcium chloride should be weighed and dissolved in 1 L of water. Three molar potassium iodide (KI) is a common electrode-filling solution. To make 500 mL of 3 Î&#x153; potassium iodide, the formula weight should first be determined. The atomic weight of potassium is 39.1 g/mol and 126.9 g/mol for iodide. The formula weight is, therefore, 166.0 g/mol. The following conversion factors can be used to find the correct amount of potassium iodide to use:
3 mol/L X 166 g/mol X 0.5 L = 249 g
NIREAS VOLUME 6 57 6.3.6.6 Normal Solutions The term normality can be used to refer to strengths of acids and bases. It indicates the amount of hydrogen ion (H+) or hydroxide ion (OH-) in a solution. In monoacidic or monobasic chemicals such as hydrogen chloride (HCl) or sodium hydroxide (NaOH), normality is equal to molarity because 1 mol of HCl contains 1 mol of hydrogen ion. In diacidic or dibasic compounds like sulfuric acid H2SO4 or calcium hydroxide Ca[OH]2, 1 mol of the chemical contains 2 mol of hydrogen or hydroxide ions so a 1-mol solution is 2 Î?. A 2-N solution will, therefore, neutralize twice the volume of a 1-N solution.
To prepare a 1-N solution of sulfuric acid, the equivalent mass should first be calculated by dividing the gram-formula weight by the number of acid hydrogens in the compound. Sulfuric acid formula weight is 98.0 g and the number of hydrogens is two; therefore, the mass is 49.0. The amount of sulfuric acid needed for 1 L of 1-N solution can be calculated as follows:
(N desired)(equivalent mass)(volume in liters desired) = (1 N) (49.0g) (1 L) = 49.0 g needed
A 1-N solution requires 49.0 g of pure sulfuric acid powder diluted to 1000 mL. However, the acid is a liquid and not pure. The volume of concentrated acid that contains 49.0 g of pure sulfuric acid can be calculated as follows:
(Grams of acid needed)/(percent concentration X specific gravity of acid) = volume of concentrated acid needed
(49.0 g)/(97% X 1.84) = 27.5 mL of concentrated H2S04 Diluting 27.5 mL of concentrated sulfuric acid will produce a 1-N solution.
6.3.6.7 Milligrams per Liter Solutions Concentration is also commonly expressed as milligrams per liter, which is the same as parts per million because 1 mL of water weighs 1 g, as follows:
1 mg/L X 1 g/1000 mg X 1 L/1000 mL X 1g/mL = 1 g/1000000 g
NIREAS VOLUME 6 58 In the 1-M calcium chloride example, simply convert grams to milligrams as follows: 110.98 g/L X 1000 mg/g = 110980 mg/L
6.3.6.8 Determining Percent Weight of Atoms in Molecules Often, the operator-analyst is only interested in the concentration of one element or constituent of a chemical compound. To determine this concentration, find the percent weight of the element in the compound by dividing the atomic weight by the formula weight. For calcium and chlorine in calcium chloride,
Ca: 40.08/110.98 X 100 = 36.11% CI: 70.90/110.98 X 100 = 63.89%
This concept becomes important in making stock and standard solutions and in how the analyte is reported. For example, phosphorus standard can be made by dissolving potassium dihydrogen phosphate (KH2PO4) in deionized water. If a 100-ppm phosphate (PO4) solution is required, the percent weight of phosphorus in potassium dihydrogen phosphate must be determined to find the weight of potassium dihydrogen phosphate to use. Then, find the percent weight of phosphorus (P), as follows:
P: 30.97/136.09 = 22.75%
One hundred milligrams of phosphorus is needed to make 1 L of solution, but only 22.75% of potassium dihydrogen phosphate is phosphorus. As an equation 100 mg Ρ = (X) mg ΚΗ2Ρ04 X 0.2275 Solving for (X),
100 mg P/ 0.2275 = 439.6 mg KH2PO4 Analytes such as phosphorus can be reported as phosphorus (indicated as PO4-,
P) or as
phosphate (indicated as PO43-), but these labels do not indicate the same thing. Similarly, ammonia (NH3) is typically reported as ammonia nitrogen (NH3-N), which is different from ammonia. The mass ratio of phosphorus to phosphate can be used to find the concentration of phosphate in the 100-ppm phosphorus standard, as follows: 100 ppm P x (94.97g/mol PO4) / (30.97 g/mol Ρ)
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6.3.7 Weighing 6.3.7.1 Analytical Balances and Weighing Conditions The ability to accurately weigh small amounts of chemicals and gravimetric dishes and filter papers for solids tests is critical to the success of the operator-analyst. A 200 g capacity analytical balance is probably the most useful weighing instrument for a small-to-medium wastewater laboratory. Analytical balances feature a draft shield over the weighing pan to minimize the effects of air currents and to guard against dust. These balances are extremely sensitive to environmental conditions and, as such, the following guidelines should be observed:
• Vibration—balances should be placed on a specially designed weighing table that features a heavy slab placed on vibration dampeners. Ideally, the table is located on the ground floor. The operator should be careful not to let the table contact a wall or laboratory bench that could cause vibration. Additionally, the operator should be aware of the proximity of equipment and machinery. • Level—the balance must be kept perfectly level. Most balances have adjustable feet and a "bull's-eye" level on one foot. • Temperature and humidity—temperature and humidity affect the internal components of the balance and should be maintained at a constant level in the laboratory. If the item being weighed is not at room temperature, it will produce air currents sufficient to cause error. Many chemicals absorb water from the air and will be difficult to accurately weigh in a highly humid environment. • Static electricity—special anti-static brushes are made for cleaning the weighing pan. Static electricity can make it difficult to transfer light chemicals and chemical flakes; it also affects the weight of diese particles. • Air currents—even light air movements, unnoticeable to the analyst, can affect the modern analytical balance. In addition to keeping the draft shield closed during weighing, the operator should keep laboratory doors and windows closed and be aware of internal currents caused by heating and ventilation systems and the fume hood. • Dust—dust accumulation in and on the balance will cause friction on moving components and, therefore, reduced accuracy. As such, the manufacturer's maintenance recommendations regarding cleaning should be followed. The operator should try to keep the laboratory isolated by keeping doors and windows closed. • As with all laboratory testing, verifying accurate and consistent readings is crucial. Therefore, it is important to regularly check the balance's calibration. The actual calibration procedure depends on the balance brand and model; the operator should check the balance's operation manual for details
NIREAS VOLUME 6 60 6.3.7.2 Weighing Containers and Accessories Chemicals or samples should never be weighed directly on the pan. There are a variety of containers designed for weighing. Disposable aluminum or plastic boats and weighing paper are the most common. Reusable ceramic boats, glass weighing bottles, and reagent funnels are also available. The operator should keep a variety of stainless steel scoops and spatulas near the balance to transfer chemicals from the bottle to the dish and to keep them clean. An anti-static balance brush is useful for brushing away spills. Oil and dust from fingerprints will make accurate use difficult. It is important to never directly touch anything that goes on the balance. Latex gloves, tongs, foreceps, and tweezers should be used to handle dishes and papers.
6.3.7.3 Drying Dishes and Reagents Dishes and papers used in gravimetric tests must be predried in the oven and/or muffle furnace. Some reagents must be dried in the oven before weighing to drive off water that may have been absorbed by the chemical. These laboratory equipment and chemicals must then be kept in a dessicator until they are cooled to ambient temperature and ready for use. A dessicator is an airtight appliance with a pan of dessicant material that adsorbs humidity preferentially to the dishes or chemical. The dessicant must occasionally be regenerated by heating in an oven to the manufacturer's specifications. To dry a chemical, the following procedures generally apply:
(1) Place a ceramic dish or glass-weighing bottle on the balance and press tare. (2) Weigh an excess amount of reagent into the container. About 20% more than is needed should be sufficient. (3) Dry the chemical in the oven according to die specific time and temperature in the reagent preparation instructions. Double check the temperature of the oven as certain chemicals can volatilize at high temperatures, even 180 째C. If drying in a container with a lid, either leave the lid off or cracked open to allow water to escape and prevent the lid from getting stuck when cooled. (4) Cool the reagent in the dessicator to room temperature.
6.3.7.4 Weighing Procedures for Reagents The following procedures should be followed to weigh reagents: (1) Turn on the balance and let it warm up 15 minutes. (2) Check the balance for level using the bull's-eye level. (3) With the draft shield closed and the pan empty, press tare or zero the balance.
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(4) When the balance reads zero, use forceps to place a calibration weight (1 to 10 g) on the pan. Most balances will give an indication on the display that the reading is stable. When the reading stabilizes, record the weight. (5) Remove the weight and ensure that the reading returns to zero. (6) Select the appropriate weighing dish and place on the pan. Choose a dish with the lightest weight possible, probably a disposable boat. (7) When the reading stabilizes, press tare. If the balance does not have a tare feature, document the beginning weight of the dish and subtract this weight from the final weight of the dish and chemical. (8) - Carefully transfer the chemical to the dish with a spatula or scoop. Add a bit at a time until you approach the desired weight. Tapping the spatula with your index finger can help add very small amounts of reagent. If you add too much and have to remove reagent, be extra careful not to bump the dish or pan and do not return the reagent to the bottle. Dispose of this reagent properly. (9) When the desired weight is displayed, close the draft shield and let the reading stabilize. Add or remove reagent to display the desired weight with the draft shield closed. (10) Remove the dish and transfer the chemical
6.3.8 Reagents 6.3.8.1 Laboratory-Grade Water Water used to prepare reagent solutions must obviously be free from contaminants, especially elements or ions for which the sample is being analyzed. Although there are a number of methods of purifying water to various specifications, a compact, wall-mounted deionizing unit is likely the best choice for a small-to-medium wastewater laboratory. These units purify water by passing it through a number of ion-exchange columns followed by final filtration through a 0.2-micron filter. The purity is indicated by electrical resistivity given in "megohm-cm", and most commercial units have a display that monitors this parameter. Once the resistivity drops below 18 Mohm-cm, the columns are spent and must be replaced. Deionized water will absorb contaminants from the air and grow microorganisms and algae if left exposed to the atmosphere and sunlight. A good rule to follow is to use fresh reagent-grade water daily.
6.3.8.2 Reagent Grades Chemical suppliers manufacture reagents to varying degrees of purity. For the analyses described in this manual, all reagents should be American Chemical Society (ACS) reagent grade. These reagents are certified to specifications given by ACS and have a guaranteed analysis and
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traceable lot number on the label. Practical and technical grade chemicals are less expensive, but are meant for use in industrial processes and are not suitable for use in an analytical laboratory. - '
6.3.8.3 Mixing Reagents The accuracy and validity of analytical results begins with quality reagents. When mixing reagents, the operator-analyst must use a proper and consistent technique that eliminates contamination and ensures a complete transfer of reagent from the weighing dish to the volumetric flask and, ultimately, to the storage bottle. This technique is known as quantitative transfer.
The operator should use the following quantitative transfer method for making reagents:
(1) Fill the volumetric flask to about 70% of the final volume; (2) If stirring is needed to dissolve the reagent in a reasonable amount of time, slide a magnetic stir bar down the neck and into the flask and put the flask on a stir plate; (3) Place a powder funnel in the neck of the flask; (4) Weigh the given amount of reagent into the proper weighing dish following the weighing procedure in Section 6.0; (5) Slowly and carefully transfer the reagent into the funnel; (6) Rinse the weighing dish into the funnel with a deionized water wash bottle. Repeat for three rinses; (7) Rinse the powder funnel with two rotations of deionized water. Repeat for three rinses; (8) Rinse the neck of the flask three times; (9) Stoppier or cover the flask and invert to mix or stir until all reagent is dissolved; (10) Remove stir bars with a Teflon-coated bar retriever. Rinse the retriever and bar into die flask with deionized water as you remove them; and (11) When the solution is at room temperature, dilute to the mark and invert to mix.
6.3.9 Making acids and bases Making acids and bases, whether for reactions, cleaning, or titrations, is one of the most common tasks in a laboratory. Although acids and bases are mixed just like reagents, it is critical that when diluting a concentrated acid or base that the acid or base is added to the water (it might be helpful for the operator to remember the following phrase: "do what you oughtta, add acid to watta"). Adding water to acids and bases produces a violent reaction and is likely to splatter from the mixing glassware. The mixing (dilution) of acids and bases results in an exothermic reaction, meaning that it produces a large amount of heat. Because of this, the operator should allow r^lenty of time for the solution to cool before diluting to the mark.
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6.3.10
Stock, standards and standards dillutions
Most analyses require preparation of a solution of known concentration of the analyte and then comparison of an unknown sample to the prepared known solution. This known solution is called a standard. The solution the standard is prepared from is called a stock solution. Diluting the standard to various concentrations (standard dilutions) enables construction of multipoint calibration curves.
6.3.10.1 Stock Solutions Stock solutions are concentrated solutions of chemicals that are diluted to make standard solutions. Stock is used because there is less uncertainty in weighing a larger amount of substance, that is, it is more accurate to weigh 1.000 g Âą 1.0 mg (0.1% uncertainty) than it is to weigh 10 mg Âą 1.0 mg (10% uncertainty)
6.3.10.2 Standard Solutions Standard solutions are made using volumetric glassware to dilute the stock solution Into the upper range of the sample being analyzed.
6.3.10.3 Standard Dilutions To make calibration curves for colorimetric procedures and calibrate electrodes and probes, the standard solution must be further diluted to a range of concentrations that are representative of the concentration of the sample being tested. If samples between 0 and 10 ppm are being measured, the standard dilutions could be prepared at 0.5,1, 2, 5, and 10 ppm. To make standard dilutions, one of the simplest and most useful equations in analytical chemistry should be used, as follows:
C1 x V1 = C2 x V2 Where C1 and V1 = the concentration and volume of the standard and C2 and V2 are the desired concentration and volume of the dilution.
The operator-analyst should use this equation to find the volume of standard needed. For example, if the operator is using a 50-ppm standard and would like to make 100 mL of 10-ppm standard dilution,
(50 ppm) x (V1) = (10 ppm) x (100 mL) (50ppm) x (V1) = 1000
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64
Therefore, to make this standard dilution, 20 mL of standard should be diluted to 100 mL of final volume. It can be helpful to make a chart of standard dilutions needed.
6.4 Materials and set-up of equipment, instruments and other devices 6.4.1 Laboratory equipment 6.4.1.1 Glassware Laboratory glassware can effectively be divided into the following two categories: volumetric and other.
Volumetric Glassware There are five pieces of volumetric glassware that are used only to accurately measure volumes of reagents. These are graduated cylinders, graduated pipets, volumetric pipets, volumetric flasks, and burets. Volumetric glassware can further be categorized as "Class A", which is the most accurate, or "Class B". Class A glass will have an evident "A" marked on it near the top. Class Î&#x2019; glass may be marked with a "B", but the absence of either mark indicates Class B. The glass should be marked with a tolerance given in milliliters, shown as "TOL Âą 2.4", for example. This is a measure of how accurately the manufacturer places lines on the glass and has nothing to do with how an analyst uses the glass. Class Î&#x2019; generally has twice the tolerance of Class A. Proper use of calibrated volumetric glass\vare requires the user to discern if the ware is calibrated "to contain" (TC) or "to deliver" (TD). Glassware is marked with a "TC" or "TD" accordingly. "To contain" indicates the vessel's calibration includes the amount of water required to wet the inner surface of the vessel in contact with the water. These vessels contain the exact volume. "To deliver" indicates the exact volume delivered or dispensed from the vessel. The two are designed for different purposes. For example, a "to contain" volumetric flask is used to dilute an original sample to a known volume; as such, it is critical that it contains the exact volume. A "to deliver" pipet may be used to transfer a solution; as such, it is critical that it delivers a known volume.
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Volumetric glassware: (left to right) volumetric flask, buret, volumetric pipet, graduated pipet, and graduated cylinder
Using Volumetric Glassware The sole use of volumetric glassware is for measuring and mixing reagents. Volumetric glassware should not be heated and reactions should not be performed in it; in addition, reagents should not be stored in volumetric flasks. Volumetric glass should be selected that measures as close to the volume needed as possible. Because the tolerance applies to every mark on the glass, the percent accuracy will decrease as less than the full volume is measured. For example, the tolerance of a Class A, 50-mL graduated cylinder is Âą0.2 mL.
Other Glassware
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Beakers and flasks make up the bulk of other glassware used in the laboratory . These are used for a variety of purposes, but primarily for carrying out reactions and analyses. Storage bottles are also common glassware. Reading volumetric glassware: (left to right) proper position for reading the 100-mL mark, glass held plumb and read at eye level, glass tilted forward or below eye level, and glass tilted backwards or above eye level
The markings on this glassware are approximate, generally good only to Âą5%, and are meant only to give the analyst a rough idea of the volume in the glass. Many of the procedures are carried out using specialized glassware. This includes items such as biochemical oxygen demand (BOD) bottles, filter flasks, filter supports, funnels, and ceramic crucibles. Specialized other glassware should be used only for the intended purpose and never as an accurate volumetric tool.
NIREAS VOLUME 6 67 BEAKERS Beakers are the most common pieces of laboratory equipment. They come in sizes from 1 mL to 4,000 mL. They are used mainly for mixing chemicals and to measure approximate volumes.
(California State University, 2008)
GRADUATED CYLINDERS Graduated cylinders also are basic to any laboratory and come in sizes from 5 mL to 4,000 mL. They are used to measure volumes more accurately than beakers.
NIREAS VOLUME 6 (California State University, 2008)
68 PIPETS
Pipets are used to deliver accurate volumes and range in size from 0.1 mL to 100 mL.
(WEF, 2012)
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BURETS Burets are also used to deliver accurate volumes. They are especially useful in a procedure called "titration." Burets come in sizes from 10 to 1,000 mL.
(WEF, 2012)
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FLASKS Flasks are used for containing and mixing chemicals. There are many different sizes and shapes.
(WEF, 2012) BOTTLES
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Bottles are used to store chemicals, to collect samples for testing purposes, and to dispense liquids
FUNNELS A funnel is used for pouring solutions or transferring
solids chemicals. This funnel also can be
used with filter paper to remove solids from a solution. A Buchner funnel is used to separate solids from a mixture. It is used with a filter flask and a vacuum.
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Separatory funnels are used to separate one chemical mix- ture from another.The separated chemical usually is dissolved in one or two layers of liquid.
TUBES Test tubes are used for mixing small quantities of chemicals. They are also used as containers for bacterial testing (culture tubes).
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6.4.1.2 Miscellaneous Laboratory Equipment Laboratory appliances are used to manipulate a sample, while laboratory instruments are used to read an analytical parameter. For example, in a solids analysis, a drying oven is an appliance used to evaporate water from a sample while an analytical balance is an instrument used to determine the mass or weight of solids. There is a wide range of miscellaneous laboratory equipment, from the smallest stir bar to the most expensive spectrophotometer. These are the tools of the operatoranalyst. Their functionality has a direct effect on the quality of results obtained. As such, they should be used only for their intended purpose and should be kept clean and well-maintained.
Miscellaneous Laboratory Equipment
Miscellaneous Laboratory Equipment
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BOD Incubator The instruments commonly used in water and wastewater analysis include the following:
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•
Analytical balance
•
pH/selective-ion meter
•
Conductivity meter
•
Turbidimeter
•
Spectrometers (visible, ultraviolet (UV), infrared (IR), and atomic absorption (AA))
•
Total carbon analyzer
•
Gas chromatograph (GC)
•
Gas chromatograph/mass spectrometer (GC/MS)
•
Temperature devices (such as ovens and water baths)
•
Recorders
Analytical balance The most important piece of equipment in any analytical laboratory is the analytical balance. The degree of accuracy of the balance is reflected in the accuracy of all data related to weightprepared standards. Although the balance should therefore be the most protected and cared-for instrument in the laboratory, proper care of the balance is frequently overlooked.
There are many fine balances on the market designed to meet a variety of needs. Types of balances include top-loading, two-pan, microanalytical, electroanalytical, semianalytical, analytical, and other special-purpose instruments. Each type of balance has its own place in the scheme of laboratory operation, but analytical single-pan balances are by far the most important in the production of reliable data.
Single-pan analytical balances range in capacity from the 20-g to the popular 200-g models with sensitivities from 0.01 to 1 mg. Features of single-pan balances may include mechanical and electronic switching of weights, digital readout, automatic zeroing of the empty balance, and automatic preweighing and taring capabilities. Even with all the design improvements, however, modem analytical balances are still fragile instruments, the operation of which is subject to shock, temperature, and humidity changes, to mishandling, and to various other insults. Some of the precautions to be observed in maintaining and prolonging the dependable life of a balance are as follows: a. Analytical balances should be mounted on a heavy, shockproof table, preferably one with an adequately large working surface and with a suitable drawer for storage of balance accessories. The balance level should be checked frequently and adjusted when necessary.
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b. Balances should be located away from laboratory traffic and protected from sudden drafts and humidity changes. c. Balance temperatures should be equilibrated with room temperature; this is especially important if building heat is shut off or reduced during nonworking hours. d. When the balance is not in use, the beam should be raised from the knife edges, the weights returned to the beam, objects such as the weighing dish removed from the pan, and the weighing compartment closed. e. Special precautions should be taken to avoid spillage of corrosive chemicals on the pan or inside the balance case; the interior of the balance housing should be kept scrupulously clean. f. Balances should be checked and adjusted periodically by a company service man or balance consultant; if service is not available locally, the manufacturerâ&#x20AC;&#x2122;s instructions should be followed as closely as possible. Service contracts, including an automatic preventive maintenance schedule, are encouraged. g. The balance should be operated at all times according to the manufacturerâ&#x20AC;&#x2122;s instructions.
Analytical balance
pH/selective-ion meter The concept of pH as a means of expressing the degree of effective acidity or alkalinity instead of total acidity or alkalinity. It was not until about 1940 that commercial instruments were developed for routine laboratory measurement of pH. A basic meter consists of a voltage source, amplifier,
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and scale or digital readout device. Certain additional refinements produce varying performance characteristics between models. Some models incorporate expanded scales for increased readability, solid state circuitry for operating stability and extreme accuracy, and temperature and slope adjustment to correct for asymmetric potential of glass electrodes. Other features are scales that facilitate use of selective-ion electrodes, recorder output, and interfacing with complex datahandling systems. In routine pH measurements the glass electrode is used as the indicator and the calomel electrode as the reference. Glass electrodes have a very fast response time in highly buffered solutions. However, accurate readings are obtained slowly in poorly buffered samples, and particularly so when changing from buffered to unbuffered samples. Electrodes, both glass and calomel, should be well rinsed with distilled water after each reading, and should be rinsed with, or dipped several times into, the next test sample before the final reading is taken. Weakly buffered samples should be stirred during measurement.
A typical pH-meter device
When not in use, glass electrodes should not be allowed to become dry, but should be immersed in an appropriate solution consistent with the manufacturerâ&#x20AC;&#x2122;s instructions. The first steps in calibrating an instrument are to immerse the glass and calomel electrodes into a buffer of known pH, set the meter to the pH of the buffer, and adjust the proper controls to bring the circuit into balance. The temperature-compensating dial should be set at the temperature of the buffer solution. For best accuracy, the instrument should be calibrated against two buffers that bracket the expected pH of the samples. The presence of a faulty electrode is indicated by failure to obtain
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a reasonably correct value for the pH of the second reference buffer solution after the meter has been standardized with the first reference buffer solution. A cracked glass electrode will often yield pH readings that are essentially the same for both standards. The response of electrodes may also be impaired by failure to maintain the KCl level in the calomel electrode, by improper electrode maintenance, or by certain materials such as oily substances and precipitates that may coat the electrode surface. Faulty electrodes can often be restored to normal by an appropriate cleaning procedure. Complete and detailed cleaning methods are usually supplied by the electrode manufacturer. Because of the asymmetric potential of the glass electrode, most pH meters are built with a slope adjustment that enables the analyst to correct for slight electrode errors observed during calibration with two different pH buffers. Exact details of slope adjustment and slope check may vary with different models of instruments. The slope adjustment must be made whenever electrodes are changed, subjected to vigorous cleaning, or refilled with fresh electrolyte. The slope adjustment feature is highly desirable and recommended for consideration when purchasing a new meter. Most pH meters now available are built with transistorized circuits rather than vacuum tubes, which greatly reduces the warmup time and increases the stability of the meters.
Also, many instruments are designed with a switching circuit so that the entire conventional 0 to 14 scale of pH may be used to read a single pH unit with a corresponding increase in accuracy.
Conductivity Meters Solutions of electrolytes conduct an electric current by the migration of ions under the influence of an electric field. For a constant applied EMF, the current flowing between opposing electrodes immersed in the electrolyte will vary inversely with the resistance of the solution. The reciprocal of the resistance is called conductance and is expressed in reciprocal ohms (mhos). For natural water samples where the resistance is high, the usual reporting unit is micromhos.
NIREAS VOLUME 6 81 A typical Conductivity Meter device
Most conductivity meters on the market today use a cathode-ray tube, commonly known as the “magic eye,” for indicating solution conductivity. A stepping switch for varying resistances in steps of 10× facilitates reading conductivities from about 0.1 to about 250,000 μmho. The sensing element for a conductivity measurement is the conductivity cell, which normally consists of two thin plates of platinized metal, rigidly supported with a very precise parallel spacing. For protection, the plates are mounted inside a glass tube with openings in the side walls and submersible end for access of sample. Variations in designs have included use of hard rubber and plastics for protection of the cell plates. Glass may be preferable, in that the plates may be visually observed for cleanliness and possible damage, but the more durable encasements have the advantage of greater protection and reduced cell breakage. Selection of various cell designs is normally based on personal preference with consideration of sample type and durability requirements.
Turbidimeters (Nephelometers) Many different instrument designs have been used for the optical measurement of turbidity by measurement of either transmission or reflection of light. An equal or even greater number of materials have been used or proposed as calibration standards. Both the analyst and the user of turbidity data should keep in mind that a turbidity measurement is not a substitute for particle weight or residue analysis. Turbidity instruments can be calibrated to give gravimetric data on
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specific sample types, but the influence of particle geometry, specific gravity, refractive index, and color make estimates of total weight impractical on a variety of sample types.
Spectrometers (See chapter Spectrophotometry )
Total organic carbon analyzer
A number of instruments designed to measure total organic carbon (TOC) in waters and wastes have appeared on the market in the past several years. The first of these units involved pyrolysis followed by IR measurement of the carbon dioxide formed. Sample injection of 20 to 200 μl in a carrier gas of air or oxygen was performed with a syringe.
A typical TOC analyzer
Combustion at 800°C to 900°C followed by IR analysis was performed automatically with final output on an analog recorder. Systems using these principles are still produced and represent a large part of the TOC market. Other techniques of TOC analysis that modify every phase of the original TOC instruments have been introduced. Sample presentation in small metallic boats and purging of CO2 from solution are two new techniques. Wet chemical oxidation, either external to the instrument or within the instrument, using various oxidants including ultraviolet irradiation is now in wide use. Measurement of the CO2 by reduction to methane (CH4) and quantitation with a
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flame ionization detector are also available. Techniques are also available for measuring materials like soil and sludges, and also the volatile component of the TOC. Sensitivity on some systems has been extended down to the microgram per liter level. The major problems associated with TOC measurements are interference from forms of inorganic carbon and the difficulty of obtaining a representative sample in the presence of particulate matter. Each system has its own procedure for sample pretreatment or for accounting for these problems. When choosing a TOC instrument, consideration should be given to the types of samples to be analyzed, the expected concentration range, and the forms of carbon to be measured.
Gas chromatograph (GC) Because GCâ&#x20AC;&#x2122;s are available from a large number of manufacturers, selection of a particular manufacturer may be based on convenience. No single multipurpose GC instrument permits analysis of a wide range of compounds. In this case, a GC/MS could be considered . If, however, relatively few types of environmentally significant compounds are being surveyed, an inexpensive system equipped with a glass-lined injection port, electrolytic conductivity detector, and analog recorder is a good choice. A review of the organic methods to be used will give the analyst all the necessary information on the specific instrument, apparatus, and materials necessary for each type or class of compounds. .Data handling requirements vary widely, and the need to automate GC data collection is determined by the extent of the sample load. In a routine monitoring laboratory, GC systems incorporating their own microprocessers and report generating capabilities would be useful in solving this problem. Because such systems greatly increase the cost, the overall economy of this choice must be considered.
Gas chromatography- Mass spectrometer schematic
6.5 Working procedures
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6.5.1 Wastewater test methods This section describes general methods to help you understand better how each works in specific test kits. Always use the specific instructions included with the equipment and individual test kits. Most water analyses are conducted either by titrimetric analyses or colorimetric analyses. Both methods are easy to use and provide accurate results.
6.5.1.1 Gravimetric Analysis In laboratory procedures classified as gravimetric analysis, the analyst measures the wastewater or sludge sample and then isolates and weighs an element or one of its compounds. Examples of gravimetric analyses are total solids (residue on evaporation), volatile solids, and suspended matter determinations.
6.5.1.2 Titrimetric Methods Titrimetric analyses are based on adding a solution of known strength (the titrant, which must have an exact known concentration) to a specific volume of a treated sample in the presence of an indicator. The indicator produces a color change indicating that the reaction is complete. Titrants are generally added by a titrator (microburet) or a precise glass pipet.
In laboratory procedures classified as volumetric analysis, the analyst measures the volume of a solution of known concentration that reacts with a particular substance in a specified volume of unknown sample. The concentration of analyte in the sample is found indirectly from the amount of the known (standard) solution that is required. As standard solution is added, a property of the solution, such as pH or millivolt potential, is monitored to indicate the completion of the reaction. Detecting the completion or "endpoint" of the volumetric reaction can also be achieved with the addition of an organic dye called an indicator that exhibits a color change at the desired endpoint pH. Volumetric analyses are commonly called titrations.
6.5.1.3 Colorimetric Methods Colorimetric standards are prepared as a series of solutions with increasing known concentrations of the constituent to be analyzed. Two basic types of colorimetric tests are commonly used: 1. The pH test measures the concentration of hydrogen ions (the acidity of a solution) determined by the reaction of an indicator that varies in color depending on the hydrogen ion levels in the water. 2. Tests based on Beer's law determine the concentration of an element or compound. Simply, Beer's law states that the higher the concentration of a substance, the darker the color produced in
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the test reaction and therefore the more light absorbed. Assuming a constant viewpath, the absorption increases exponentially with concentration.
Colorimetric methods of analysis have been developed for several parameters providing faster, more economical, and convenient ways of obtaining quantitative laboratory data. For a colorimetric method to be quantitative, it must form a compound with definite color characteristics that are directly proportional to the concentration of the substance being measured. Colorimetric measurements may be made with a wide range of equipment. The wastewater treatment plant (VVWTP) operator may use standard color-comparison tubes, photoelectric colorimeters, or spectrophotometers; each has its place and particular application in wastewater analysis. Colorcomparison tubes, sometimes referred to as Nessler lubes, have been standard equipment for making colorimetric measurements for many years. Precise work with color-comparison tubes requires the use of optically matched tubes. The main difficulty with their use is that standard color solutions are often unstable, and every time a determination has to be made it becomes necessary to prepare a series of fresh standards. Use of color tubes and standards is rapidly being replaced by photoelectric and spectrophotometric methods, largely because of their convenience and accuracy. Spectrophotometers are discussed in detail in next section.
6.5.1.4 Visual Methods An octet comparator uses standards that are mounted in a plastic comparator block. It employs eight permanent translucent color standards and built-in filters to eliminate optical distortion. The sample is compared using either of two viewing windows. Two devices that can be used with the comparator are the bicolor reader, which neutralizes color or turbidity in water samples, and viewpath, which intensifies faint colors of low concentrations for easy distinction.
6.5.1.5 Electronic Methods Although the human eye is capable of differentiating color intensity, interpretation is quite subjective. Electronic colorimeters consist of a light source that passes through a sample and is measured on a photode-tector with an analog or digital readout. Besides electronic colorimeters, specific electronic instruments are manufactured for lab and field determination of many water quality factors, including pH, total dissolved solids (TDS)/conductivity, dissolved oxygen, temperature, and turbidity.
These instrumental methods rely on the measurement of the electrical current or potential generated in the sample to indicate the concentration of a particular substance. A probe that is manufactured to select for a particular analyte (ion-selective electrode) is connected to a meter
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that measures the current across the probe. The meter and probe are calibrated against a range of standard solutions, and the resulting calibration curve is stored in the meter software.
6.5.1.6 pH Measurement pH is defined as the negative log of the hydrogen ion concentration of the solution. This is a measure of the ionized hydrogen in solution. Simply, it is the relative acidity or basicity of the solution. The chemical and physical properties and the reactivity of almost every component in water are dependent upon pH, which relates to corrosivity, contaminant solubility, and conductance of the water. pH has a secondary maximum contaminant level (MCL) set at 6.5 to 8.
Analytical and Equipment Considerations The pH can be analyzed in the field or in the lab. If analyzed in the lab, it must be measured within 2 hours of sample collection, because the pH will change due to carbon dioxide in air that dissolves in the water, bringing the pH closer to 7. If your program requires a high degree of accuracy and precision in pH results, the pH should be measured with a laboratory-quality pH meter and electrode.
pH Meters A pH meter measures the electric potential (millivolts) across an electrode when immersed in water. This electric potential is a function of the hydrogen ion activity in the sample; therefore, pH meters can display results in either millivolts (mV) or pH units. A pH meter consists of a potentiometer, which measures electric potential where it meets the water sample; a reference electrode, which provides a constant electric potential; and a temperature compensating device, which adjusts the readings according to the temperature of the sample (because pH varies with temperature). The reference and glass electrodes are frequently combined into a single probe called a combination electrode. A wide variety of meters is available, but the most important part of the pH meter is the electrode; thus, it is important to purchase a good, reliable electrode and follow the manufacturer's instructions for proper maintenance. Infrequently used or improperly maintained electrodes are subject to corrosion, which makes them highly inaccurate.
pH "Pocket Pals" and Color Comparators pH "pocket pals" are electronic handheld "pens" that are dipped in the water, providing a digital readout of the pH. They can be calibrated to only one pH buffer. (Lab meters, on the other hand, can be calibrated to two or more buffer solutions and thus are more accurate over a wide range of
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pH measurements.) Color comparators involve adding a reagent to the sample that colors the sample water. The intensity of the color is proportional to the pH of the sample, then matched against a standard color chart. The color chart equates particular colors to associated pH values, which can be determined by matching the colors from the chart to the color of the sample. For instructions on how to collect and analyze samples, refer to Standard Methods.
6.5.1.7 Chlorine Residual Testing/Analysis Chlorination is the most widely used means of disinfecting water in the United States. When chlorine gas is dissolved into (pure) water, it forms hypochlorous acid (HOCl), hypochlorite (OCl) ions, and hydrogen chloride (hydrochloric acid). The total concentration of HOCl and OCl ions is known as free chlorine residual. Some of the most popular methods for determination of total chlorine residual are the following:
1. spectrophotometric 2.(ferrous ammonium sulfate) titration 3. Direct amperometric titration 4. Direct iodometric titration
Note: Treatment facilities required to meet nondetectable total chlorine residual limitations must use one of the test methods specified in the plant's NPDES discharge permit.
For information on any of the other approved methods, refer to the appropriate reference cited in the national regulations.
NIREAS VOLUME 6 88 6.5.1.8 Dissolved Oxygen Testing MORE A stream system used as a source of water produces and consumes oxygen. It gains oxygen from the atmosphere and from plants through photosynthesis. Churning running water dissolves more oxygen than still water does, such as in a reservoir behind a dam. Respiration by aquatic animals, decomposition, and various chemical reactions consume oxygen. Oxygen is actually poorly soluble in water. Its solubility is related to pressure and temperature. In water supply systems, dissolved oxygen (DO) in raw water is considered the necessary element to support life for many aquatic organisms. From the drinking water practitioner's point of view, DO is an important indicator of the water treatment process and an important factor in corrosivity. Wastewater from sewage treatment plants often contains organic materials that are decomposed by microorganisms that use oxygen in the process. The amount of oxygen consumed by these organism in breaking down the waste is known as the biochemical oxygen demand (BOD). Other sources of oxygen-consuming waste include stormwater runoff from farmland or urban streets, feedlots, and failing septic systems. Oxygen is measured in its dissolved form as dissolved oxygen. If more oxygen is consumed than produced, DO levels decline and some sensitive animals may move away, weaken, or die. DO levels fluctuate over a 24-hour period and seasonally, and they vary with water temperature and altitude. Cold water holds more oxygen than warm water. and water holds less oxygen at higher altitudes. Thermal discharges (such as water used to cool machinery in a manufacturing plant or a power plant) raise the temperature of water and lower its oxygen content. Aquatic animals are most vulnerable to lowered DO levels in the early morning on hot summer days, when stream flows are low, water temperatures are high, and aquatic plants have not been producing oxygen since sunset.
Sampling and Equipment Considerations In contrast to lakes, where DO levels are most likely to vary vertically in the water column, changes in DO in rivers and streams move horizontally along the course of the waterway. This is especially true in smaller, shallow streams. In larger, deeper rivers, some vertical stratification of dissolved oxygen might occur. The DO levels in and below riffle areas, waterfalls, or dam spillways are typically higher than those in pools and slower-moving stretches. If you wanted to measure the effect of a dam, sampling for DO behind the dam immediately below the spillway and upstream of the dam would be important. Because DO levels are critical to fish, a good place to sample is in the pools that fish tend to favor, or in the spawning areas they use.
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An hourly time profile of DO levels at a sampling site represents a valuable set of data, because it shows the change in DO levels from the low point (just before sunrise) to the high point (sometime near midday). This might not be practical for a volunteer monitoring program, though. Note the time of your DO sampling to help judge when in the daily cycle the data were collected. DO is measured in either milligrams per liter MAXIMUM DISSOLVED OXYGEN (DO) CONCENTRATIONS VS. TEMPERATURE VARIATIONS
Temperature (째C)
Temperature DO
(째C)
DO (mg/L)
(mg/L) 0
14.60
23
8.56
1
14.19
24
8.40
2
13.81
25
8.24
3
13.44
26
8.09
4
13.09
27
7.95
5
12.75
28
7.81
6
12.43
29
7.67
7
12.12
30
7.54
S
11.83
31
7.41
9
11.55
32
7.28
10
11.27
33
7.16
11
11.01
34
7.05
12
10.76
35
6.93
13
10.52
36
6.82
14
10.29
37
6.71
15
10.07
38
6.61
16
9.85
39
6.51
17
9.65
40
6.41
18
9.45
41
6.31
19
9.26
42
6.22
20
9.07
43
6.13
21
8.90
44
6.04
22
8.72
45
5.95
(Frank R. Spellman, 2011)
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(mg/L) or percent saturation, which is the amount of oxygen in a liter of water relative to the total amount of oxygen that the water can hold at that temperature. Dissolved oxygen samples are collected using a special BOD bottle: a glass bottle with a "turtleneck" and a ground stopper. You can fill the bottle directly in the stream if the stream is wadeable or can be accessed by boat, or you can use a sampler dropped from a bridge or boat into water deep enough to submerse it. Samplers can be made or purchased.
Dissolved oxygen is measured primarily by using some variation of the Winkler method or a meter and probe.
Winkler Method (Azide Modification) The Winkler method (azide modification) involves filling a sample bottle completely with water (no air is left to bias the test). The dissolved oxygen is then fixed using a series of reagents that form a titrated acid compound. Titration involves the drop-by-drop addition of a reagent that neutralizes the acid compound, causing a change in the color of the solution. The point at which the color changes is the endpoint, which reflects the amount of oxygen dissolved in the sample. The sample is usually fixed and titrated in the field at the sample site. Preparing the sample in the field and delivering it to a lab for titration is also possible. The azide modification method is best suited for relatively clean waters; otherwise, substances such as color, organics, suspended solids, sulfide, chlorine, and ferrous and ferric iron can interfere with test results. If fresh azide is used, nitrite will not interfere with the test. In testing, iodine is released in proportion to the amount of DO present in the sample. By using sodium thiosulfate with starch as the indicator, the sample can be titrated to determine the amount of DO present.
Meter and Probe A dissolved oxygen meter is an electronic device that converts signals from a probe placed in the water into units of DO in milligrams per liter. Most meters and probes also measure temperature. The probe is filled with a salt solution and has a selectively permeable membrane that allows DO to pass from the streamwater into the salt solution. The DO that has diffused into the salt solution changes the electric potential of the salt solution, and this change is sent by electric cable to the meter, which converts the signal to milligrams per liter on a scale that the user can read.
Methodology
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If samples are to be collected for analysis in the laboratory, a special American Public Health Association (APHA) sampler, or the equivalent, must be used. If the sample is exposed or mixed with air during collection, test results can change dramatically; therefore, the sampling device must allow collection of a sample that is not mixed with atmospheric air and must allow for at least 3x bottle overflow . Again, because the DO level in a sample can change quickly, only grab samples should be used for dissolved oxygen testing. Samples must be tested immediately (within 15 minutes) after collection.
Note: Samples collected for analysis using the modified Winkler titration method may be preserved for up to 8 hours by adding 0.7 mL of concentrated sulfuric acid or by adding all the chemicals required by the procedure. Samples collected from the aeration tank of the activated sludge process must be preserved using a solution of copper sulfate-sulfamic acid to inhibit biological activity.
The advantage of using the DO oxygen meter method is that the meter can be used to determine DO concentration directly . In the field, a direct reading can be obtained using a probe or samples can be collected for testing in the laboratory using a laboratory probe.
The probe used in the determination of DO consists of two electrodes, a membrane, and a membrane filling solution. Oxygen passes through the membrane into the filling solution and causes a change in the electrical current passing between the two electrodes. The change is measured and displayed as the concentration of DO. To be accurate, the probe membrane must be in proper operating condition, and the meter must be calibrated before use. The only chemical used in the DO meter method during normal operation is the electrode filling solution; however, in the Winkler DO method, chemicals are required for meter calibration.
Key Point: The field probe can be used for laboratory work by placing a stirrer in the bottom of the sample bottle, but the laboratory probe should never be used in any situation where the entire probe might be submerged.
Calibration prior to use is important. Both the meter and the probe must be calibrated to ensure accurate results. The frequency of calibration is dependent on the frequency of use; for example, if the meter is used once a day, then calibration should be performed before use. Three methods are available for calibration: saturated water, saturated air, and the Winkler method. It is important to
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note that, if the Winkler method is not used for routine calibration method, periodic checks using this method are recommended.
6.5.1.9 Biochemical Oxygen Demand Testing More Biochemical oxygen demand (BOD) measures the amount of oxygen consumed by microorganisms in decomposing organic matter in streamwater. BOD also measures the chemical oxidation of inorganic matter (the extraction of oxygen from water via chemical reaction). A test is used to measure the amount of oxygen consumed by these organisms during a specified period of time (usually 5 days at 20°C). The rate of oxygen consumption in a stream is affected by a number of variables: temperature, pH, the presence of certain kinds of microorganisms, and the type of organic and inorganic material in the water. Biochemical oxygen demand directly affects the amount of dissolved oxygen in water bodies—the greater the BOD, the more rapidly oxygen is depleted in the water body, leaving less oxygen available to higher forms of aquatic life. The consequences of high BOD are the same as those for low dissolved oxygen: Aquatic organisms become stressed, suffocate, and die. Most river waters used as water supplies have a BOD less than 7 mg/L; therefore, dilution is not necessary. Sources of BOD include leaves and wood debris; dead plants and animals; animal manure; effluents from pulp and paper mills, wastewater treatment plants, feedlots, and food-processing plants; failing septic systems; and urban stormwater runoff.
Note: To evaluate the potential use of raw water as a drinking water supply, it is usually sampled, analyzed, and tested for biochemical oxygen demand when turbid, polluted water is the only source available.
Sampling Considerations Biochemical oxygen demand is affected by the same factors that affect dissolved oxygen. Aeration of streamwater (e.g., by rapids and waterfalls) will accelerate the decomposition of organic and inorganic material; therefore, BOD levels at a sampling site with slower, deeper waters might be higher for a given column of organic and inorganic material than the levels for a similar site in highly aerated waters. Chlorine can also affect BOD measurement by inhibiting or killing the microorganisms that decompose the organic and inorganic matter in a sample. If sampling in chlorinated waters (such as those below the effluent from a sewage treatment plant), neutralizing the chlorine with sodium thio-sulfate is necessary (see Standard Methods). Biochemical oxygen demand measurement requires taking two samples at each site. One is tested immediately for dissolved oxygen; the second is incubated in the dark at 20°C for 5 days and then
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tested for dissolved oxygen remaining. The difference in oxygen levels (in mg/L) between the first test and the second test is the amount of BOD. This represents the amount of oxygen consumed by microorganisms and used to break down the organic matter present in the sample bottle during the incubation period. Because of the 5-day incubation, the tests are conducted in a laboratory. Sometimes by the end of the 5-day incubation period, the dissolved oxygen level is zero. This is especially true for rivers and streams with a lot of organic pollution. Because knowing when the zero point was reached is not possible, determining the BOD level is also impossible. In this case, diluting the original sample by a factor that results in a final dissolved oxygen level of at least 2 mg/L is necessary. Special dilution water should be used for the dilutions (see Standard Methods). Some experimentation is needed to determine the appropriate dilution factor for a particular sampling site. The result is the difference in dissolved oxygen between the first measurement and the second, after multiplying the second result by the dilution factor. Standard Methods prescribes all phases of procedures and calculations for BOD determination. A BOD test is not required for monitoring water supplies.
6.5.1.10 Solids Measurement Solids in water are defined as any matter that remains as residue upon evaporation and drying at 103°C. They are separated into two classes: suspended solids and dissolved solids.
Total Solids = Suspended Solids (nonfilterable residue) + Dissolved Solids (filterable residue)
As shown above, total solids are dissolved solids plus suspended and settleable solids in water. In natural freshwater bodies, dissolved solids consist of calcium, chlorides, nitrate, phosphorus, iron, sulfur, and other ions—particles that will pass through a filter with pores of around 2 μm (0.002 mm) in size. Suspended solids include silt and clay particles, plankton, algae, fine organic debris, and other particulate matter. These are particles that will not pass through a 2-μm filter.
The concentration of total dissolved solids affects the water balance in the cells of aquatic organisms. An organism placed in water with a very low level of solids (distilled water, for example) swells because water tends to move into its cells, which have a higher concentration of solids. An organism placed in water with a high concentration of solids shrinks somewhat, because the water in its cells tends to move out. This in turn affects the organism's ability to maintain the proper cell density, making it difficult for it to maintain its position in the water column. It might float up or sink down to a depth to which it is not adapted, and it might not survive. Higher concentrations of suspended solids can serve as carriers of toxics, which readily cling to suspended particles. This is particularly a concern where pesticides are being used on irrigated
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crops. Where solids are high, pesticide concentrations may increase well beyond those of the original application as the irrigation water travels down irrigation ditches. Higher levels of solids can also clog irrigation devices and might become so high that irrigated plant roots will lose water rather than gain it. A high concentration of total solids will make drinking water unpalatable and could have an adverse effect on people who are not used to drinking such water. Levels of total solids that are too high or too low can also reduce the efficiency of wastewater treatment plants, as well as the operation of industrial processes that use raw water. Total solids affect water clarity. Higher solids decrease the passage of light through water, thereby slowing photosynthesis by aquatic plants. Water heats up more rapidly and holds more heat; this, in turn, might adversely affect aquatic life adapted to a lower temperature regime. Sources of total solids include industrial discharges, sewage, fertilizers, road runoff, and soil erosion. Total solids are measured in milligrams per liter.
Solids Sampling and Equipment Considerations When conducting solids testing, many things can affect the accuracy of the test or result in wide variations in results for a single sample: 1. Drying temperature 2. Length of drying time 3. Condition of desiccator and desiccant 4. A lack of consistency among nonrepresentative samples in the test procedure 5. Failure to achieve constant weight prior to calculating results
Several precautions can be taken to improve the reliability of test results:
1. Use extreme care when measuring samples, weighing materials, and drying or cooling samples. 2. Check and regulate oven and furnace temperatures frequently to maintain the desired range. 3. Use an indicator drying agent in the desiccator that changes color when it is no longer good; change or regenerate the desiccant when necessary. 4. Keep the desiccator cover greased with the appropriate type of grease; this will seal the desiccator and prevent moisture from entering the desiccator as the test glassware cools. 5. Check ceramic glassware for cracks and glass fiber filters for possible holes. A hole in a glass filter will cause solids to pass through and give inaccurate results. 6. Follow manufacturers' recommendations for the care and operation of analytical balances.
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Total solids are important to measure in areas where discharges from sewage treatment plants, industrial plants, or extensive crop irrigation may occur. In particular, streams and rivers in arid regions where water is scarce and evaporation is high tend to have higher concentrations of solids and are more readily affected by the human introduction of solids from land-use activities.
Total solids measurements can be useful as an indicator of the effects of runoff from construction, agricultural practices, logging activities, sewage treatment plant discharges, and other sources. As with turbidity, concentrations often increase sharply during rainfall, especially in developed watersheds. They can also rise sharply during dry weather if earth-disturbing activities occur in or near the stream without erosion control practices in place. Regular monitoring of total solids can help detect trends that might indicate increasing erosion in developing watersheds. Total solids are closely related to stream flow and velocity and should be correlated with these factors. Any change in total solids over time should be measured at the same site at the same flow.
Total solids are measured by weighing the amount of solids present in a known volume of sample; this is accomplished by weighing a beaker, filling it with a known volume, evaporating the water in an oven and completely drying the residue, then weighing the beaker with the residue. The total solids concentration is equal to the difference between the weight of the beaker with the residue and the weight of the beaker without it. Because the residue is so light in weight, the lab needs a balance that is sensitive to weights in the range of 0.0001 g. Balances of this type are called analytical or Mettler balances, and they are expensive (around $3000). The technique requires that the beakers be kept in a desiccator, a sealed glass container containing material that absorbs moisture and ensures that the weighing is not biased by water condensing on the beaker. Some desiccants change color to indicate moisture content. Measurement of total solids cannot be done in the field. Samples must be collected using clean glass or plastic bottles or Whirl-Pak速 bags and taken to a laboratory where the test can be run.
Total Suspended Solids The term solids refers to any material suspended or dissolved in water and wastewater. Although normal domestic wastewater contains a very small amount of solids (usually less than 0.1%), most treatment processes are designed specifically to remove or convert solids to a form that can be
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removed or discharged without causing environmental harm. In sampling for total suspended solids (TSS), samples may be either grab or composite and can be collected in either glass or plastic containers. TSS samples can be preserved by refrigeration at or below 4°C (not frozen); however, composite samples must be refrigerated during collection. The maximum holding time for preserved samples is 7 days.
Volatile Suspended Solids Testing When the total suspended solids are ignited at 550 ± 50°C, the volatile (organic) suspended solids of the sample are converted to water vapor and carbon dioxide and are released to the atmosphere. The solids that remain after the ignition (ash) are the inorganic or fixed solids. In addition to the equipment and supplies required for the total suspended solids test, you need the following: 1. Muffle furnace (550 ± 50°C) 2. Ceramic dishes 3. Furnace tongs 4. Insulated gloves
6.5.2 Spectrophotometry The spectrophotometer has become an even more important analytical instrument for the examination of wastewater in recent years. Results obtained from spectrophotometric methods are generally more versatile, accurate, and reproducible than older, competing methods based on wet chemistry. Because they are not dependent on the limitations of eyesight of an analyst, the results are statistically superior to colorimetric methods where an analyst must compare colors, for example. Specific methods or spectrophotometers will not be detailed in this chapter; instead, operation theory and tips to keep performance and productivity at a high level will be presented.
Spectrophotometric methods, as with just about any of the more modern instrument-based methods, have many advantages including minimization of human bias and error, efficient and accurate data handling, and safety. The methods are generally not susceptible to different analysts' eyesight differences or color interpretations and are not even limited to visible colors (i.e., they can be used to measure light that is outside the ability of humans to detect). Typically, less sample preparation is required than a conventional or wet method and there is less opportunity to contaminate the test specimen chemically or physically. In addition, modern automation, such as robotics and autosamplers, can allow many samples to be run efficiently.
NIREAS VOLUME 6 97 6.5.2.1 Fundamentals of the technology Spectrophotometers use the interaction of light energy with a material to perform an analysis. The graphical data obtained are typically displayed as a spectrum. A spectrum is a plot of the intensity, absorbance, or similar measure of detection vs the wavelength (frequency or wavenumber) of the energy. Interpretation of the spectrum and spectral data can provide more information about the sample than a conventional (wet) method. Atomic and molecular energy levels, molecular geometries, chemical bonds, interactions of molecules, and related processes can sometimes be inferred from a spectrum. Often, spectra are used to identify chemical species (i.e., for qualitative analysis). Spectra may also be used to measure the amount or concentration of material in a sample (i.e., for quantitative analysis).
Schematic of a wavelength-selectable, single-beam UV-Vis spectrophotometer
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NIREAS VOLUME 6 99 A typical spectrophotometer
A spectrometer is an instrument for measuring the amount of light or radiant energy transmitted through a solution or solid material as a function of wavelength. A spectrometer differs from a filter photometer in that it uses continuously variable, and more nearly monochromatic, bands of light. Because filter photometers lack the versatility of spectrometers, they are used most profitably where standard methodologies are used for routine analysis.
The essential parts of a spectrometer include the following: a. A source of radiant energy b. Monochromator or other device for isolating narrow spectral bands of light c. Cells (cuvettes) or sample holders for containing samples under investigation d. A photodetector (a device to detect and measure the radiant energy passing through the sample)
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MORE Terminology A photometer is a device that measures light intensity. A colorimeter is a device that measures color intensity. Color comparators can also be put into this group of devices. When using color comparators, an analyst prepares a colored Sample and compares (by visual inspection) with tubes or other color standards to obtain a concentration of the analyte. Color comparators are still found in many applications in modern laboratories. A spectrophotometer uses the concepts of a spectrum and a photometer to measure a specific analyte. The light is split into a spectrum (of colors, some of which may not be visible to the human eye), and measures the light intensity caused by a specific color. The spectrum or color differences are caused by different wavelengths (or frequencies) of the light. The part of the molecule that causes the spectral absorbance is sometimes termed the chroniophore, which is Latin for "color body".
The following are a few facts about spectra and spectrophotometers:
• Visible while light is the summation of light of all visible colors. • Colored light has some wavelengths present and some missing. • Something appears black when there Is little or no light being transmitted to one's eye from the object. • Either a prism or grating in the instrument splits the light into its spectral wavelengths. These disperse the light and are termed dispersive elements. (It is important to note that some spectrophotometers use nondispersive technology, such as filters or Fourier-transform technology). • Visible light can be described as being made up of the following colors, from long wavelengths to short wavelengths: red, orange, yellow, green, blue, indigo, violet ("ROYGBIV" is a useful abbreviation to remember). • Infrared is invisible light with a longer wavelength than red. • Ultraviolet is invisible light with a shorter wavelength than violet. • Infrared and UV spectrophotometers are fairly common. Instruments for visible wavelengths often incorporate UV and are called UV and visible spectrophotometers.
Because of the spectrophotometer's design, interferences are minimized. Analytes typically absorb only the wavelength of light being measured in the spectrophotometer and interferences typically do not absorb this wavelength. As such, a spectrophotometric test typically minimizes interferences. Units of measure in spectrophotometric methods depend on the type of spectrum.
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Because the spectrum is typically the item to think about in this analysis, the two most common units used are units of intensity at the detector and units of wavelength. Wavelength is a description of a property of the light waves. It is the length of one complete wave of light. Wavelength units in the visible and UV region are typically nanometers (nm). Frequency can also be used. Frequency units are typically in Hertz, (Hz), or waves per second or cycles per second (1 Hz = I cycle/second). Frequency (of light) multiplied by its wavelength gives, as an example, length per second, which is a speed (i.e., the speed of light). The amplitude of a wave is its height, and is indicative of its intensity.
In an infrared spectrum, instead of wavelength, wavenumber is often used on the horizontal axis. Wavenumber is the number of waves per unit of length, where wavelength is the length of one wave. Frequency is the number of waves per unit of time. For example, a midinfrared wavenumber would be about 1000 waves/centimeter. Typically, the "waves" term is left out, so 1000 wavenumbers would appear as 1000 cm-1. Absorbance is a measure of the ratio of intensity of the sample to the blank intensity. The blank is the test specimen or sample without analyte (e.g., typically pure water [sometimes "air" without water is used as a blank]). Typically, the vertical scale of the spectrum is labeled with "absorbance"; these units are abbreviated as "Abs" or "Abs units". These can actually be termed "unit-less" numbers (intensity/intensity). Sometimes, the vertical scale will be labeled with "intensity". In infrared spectra, units are often referred to as "transmittance", which is related to absorbance and is typically expressed as a percent or fraction. One form of the Beer Lambert Law equation, as it is typically used for liquids, is: I/Io = 10-Îąl, where: Io = intensity of light striking a substance through which light can be transmitted, in units like W/m2 I = intensity of light transmitted through the substance, in the same units as Io l = the distance that light travels through the substance, in m
NIREAS VOLUME 6 102 Typical depiction of Beer-Lambert law with mathematical relationship
For example, when the intensity of light through the sample is the same as that through the background or blank (in a certain range of the spectrum), this would be expressed as 100% transmittance . One reason transmittance is sometimes used is that smaller peaks are easier to interpret for qualitative analysis purposes. For quantitative analysis, which is the biggest use in water testing, absorbance is easier to use because of the linear relationship in the Beer-Lambert law.
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6.6 Analytical methods A full spectrum of water and wastewater testing can be performed to evaluate the specific characteristics of water, wastewater or treated effluent. The ability to determine what is happening within a plant, including evaluations of plant performance, can only be done when proper sampling, storage and transportation techniques have been followed
7.1.1 Total Suspended Solids (TSS) 7.1.2 Volatile Suspended Solids (VSS) 7.1.3 Mixed Liquor Suspended Solids (MLSS) 7.1.4 Mixed Liquor Volatile Suspended Solids (MLVSS) 7.1.5 Total Solids (TS) 7.1.6 Total Dissolved Solids (TDS) 7.1.7 Settleable Solids 7.1.8 Settled Sludge Volume 7.1.9 Sludge Volume Index (SVI) 7.1.10 Acid/Alkaline (pH) 7.1.11 Dissolved Oxygen (DO) 7.1.12 Total Residual Chlorine (TRC) 7.1.13 Ammonia Nitrogen (NH3-N) 7.1.14 Nitrite Nitrogen (NO2-N) 7.1.15 Nitrate Nitrogen (NO3-N) 7.1.16 Total Kjeldahl Nitrogen (TKN) 7.1.17 Oil and Grease (O&G) 7.1.18 Total Phosphorus as P (TP) 7.1.19 Chemical Oxygen Demand (COD) 7.1.20 Alkalinity 7.1.21 Biochemical Oxygen Demand (BOD5) 7.1.22 Carbonaceous Biochemical Oxygen Demand (CBOD5) 7.1.23 Total Coliform (multiple-tube fermentation technique) 7.1.24 Fecal Coliform (membrane filter procedure) 7.1.25 Escherichia Coliform (membrane filter procedure)
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6.7 Safety and Hygiene Like most accidents, laboratory accidents happen when work is rushed and a worker's attention is distracted. Therefore, it is important for the operator to work steadily and methodically and to minimize diversions. The operator should conduct himself or herself responsibly at all times in the laboratory. Indeed, safety procedures cannot be overemphasized. Before starting, the operator should be familiar with all procedures and the hazards involved. The operator is responsible for his or her own safety and the safety of those around him or her. The operator should develop a chemical hyg iene plan that includes a list of all chemicals stored in the laboratory in addition to chemical hazards, emergency procedures, and spill cleanup protocol. The specifics of an operator's laboratory should be included in the plan. The plan should also be reviewed with all personnel using the laboratory and updated annually.
The following subsections contain general safety guidelines for a wastewater laboratory.
6.7.1 Personal Protective Equipment Use of personal protective equipment (PPE) in the laboratory is required. Eye, hand, ear, and clothing protection, such as the following, are the minimum requirements .
â&#x20AC;˘ Safety goggles offer a high degree of protection. Safety glasses are acceptable but should be designed to protect from splashing. Face shields are recommended on occasion (i.e., when sampling ports are at eye level and when working with concentrated reagents or hot materials);
â&#x20AC;˘ Disposable latex gloves, preferably powder-free, are the most common type of hand protection. Nitrile gloves should be substituted if latex allergies are an issue. Reusable gauntlet-style gloves should also be available.
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â&#x20AC;˘ It is important to dress appropriately for laboratory work. Closed-toe shoes (preferably chemicalresistant) and long pants should be worn, long hair should be tied back, and shirt tails should be tucked in. In addition, a laboratory coat and rubber apron should be worn when needed.
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6.7.2 Chemical Storage Labeling is the primary rule of chemical storage. All chemicals and reagents should be clearly labeled with the date received, date opened, and initials of the individual responsible. If not prelabeled by a manufacturer, the substance name, concentration, and expiration date should be labeled and a National Fire Protection Association symbol should be affixed to the containment bottle. Chemicals should be used on a "first in first out" basis so they are not wasted and do not expire before use. Chemicals should be stored in cabinets or where there is no risk that they will be accidentally knocked over. Caution must be used when storing chemicals of different hazard classes. The following items should not be stored together: strong oxidizers and reducing chemicals; strong acids and bases; or oxidizers, flammables,.and combustibles. Spills in the storage area can be dangerous when hazard classes mix. If separate storage areas are not available, the smallest amounts of chemical available should be stored. The operator should plan for storage and use of chemicals to minimize the amount of chemical stored or used. This will achieve safe operation of the laboratory. Compressed gas cylinders should be stored upright and chained in separate, ventilated areas, hi addition, oxygen cylinders should be stored away from other cylinders. Every chemical stored in the laboratory must be accompanied by a material safety data sheet (MSDS), which is readily available. The MSDS should be read for all chemicals that will be handled. The operator should follow recommendations for safe use and disposal of materials.
6.7.3 Chemical Handling (1) Chemicals should be handled with a spatula, spoon, tongs, or a pipet fitted with a suction bulb. Chemicals should never be handled with bare hands and should never be pipetted by mouth. In addition, chemicals should never be returned to reagent bottles. (2) Every sample should be handled as if it is pathogenic. Similarly, every chemical should be handled as if it were hazardous. When working with hazardous materials such as volatile solvents, bases, or acids, the operator should work under a ventilated fume hood. (3) Each chemical's MSDS sheet should be consulted for specific disposal instructions. When proper disposal involves disposing of chemicals down the sink, the sink should be flushed with plenty of water because the plumbing system can hold vapor pockets or be damaged by strong acids and bases.
6.7.4 Chemical Spills Chemical spills, whether they are a solid chemical, acid, base, or mixed reagent, are inevitable in the course of laboratory work. The operator should be prepared to handle spills by having a
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chemical safety plan and readily available safety equipment. Laboratory-specific spill containment kits are commercially available and should be standard safety equipment. The following are some important factors regarding handling of chemical spills: • Spills at a laboratory should be cleaned up immediately and all work areas should be cleaned before leaving the laboratory; • Access to shut-off valves should never be blocked; • The operator should identify and know how to use safety equipment, including the eyewash and emergency shower station. A routine schedule should be established for flushing eyewashes and safety showers and to verify they are functioning properly. Access to the emergency station should never be blocked; • If a person is splashed with acid, large volumes of water are required immediately to prevent serious burns. Clothing, belts, and shoes that might trap acid against the skin should be removed immediately upon entering the emergency shower because confining heat generated by the reaction could increase the severity of skin burns; • A first aid kit should be readily available.
6.7.5 Fire All state, local, and other regulatory agency criteria on placement and use of fire extinguishers and equipment should always be followed. An ABC-rated fire extinguisher must be wall-mounted in a conspicuous and accessible area of the laboratory. In addition, a fire blanket should be available to wrap and extinguish a person who has caught fire. Fire regulations concerning storage quantities, types of approved containers and cabinets, proper labeling, and so on should be complied with. Chemical storage areas should always be labeled. The reaction of water with many chemicals is exothermic, producing heat. Operators should work closely with local fire departments so they are aware of the unique hazards a wastewater laboratory and treatment plant present.
6.7.6 Ingestion Hazards Care must be taken to avoid ingestion of chemicals used in analyses and the infectious materials found in wastewater and sludge samples. These can be ingested through the mouth, absorbed through the skin, or inhaled to the lungs. The following rules should be followed: • Never eat, drink, or smoke while working in the laboratory; • Never store food in laboratory refrigerators (personal food should be stored in a separate area);
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â&#x20AC;˘ Remove laboratory gloves and coats before leaving the laboratory. Wash your hands before lea\ang the laboratory and before eating; and â&#x20AC;˘ The laboratory must be well-ventilated to avoid buildup of dangerous vapors.
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GLOSSARY
6.8 Glossary 7-day average concentration The arithmetic average of all effluent samples, composite or grab as required by the permit, within a period of one calendar week, Sunday through Saturday. absorption (1) Taking up of matter in bulk by other matter, as in dissolving of a gas by a liquid. (2) Penetration of substances into the bulk of the solid or liquid. See also adsorption. absorption capacity A measure of the quantity of a soluble substance that can be absorbed by a given quantity of a solid substance. acclimation The dynamic response of a system to the addition or deletion of a substance until equilibrium is reached; adjustment to a change in the environment. accuracy The absolute nearness to the truth. In physical measurements, it is the degree of agreement between the quantity measured and the actual quantity. It should not be confused with precision, which denotes the reproducibility of the measurement. acid (1) A substance that tends to lose a proton. (2) A substance that dissolves in water with the formation of hydrogen ions. (3) A substance containing hydrogen that may be replaced by metals to form salts. acid-forming bacteria Microorganisms that can metabolize complex organic compounds under anaerobic conditions. This metabolic activity is the first step in the two-step anaerobic fermentation process leading to the production of methane. acidity The quantitative capacity of aqueous solutions to neutralize a base; measured by titration with a standard solution of a base to a specified endpoint; typically expressed as calcium carbonate equivalents (mg/L CaC03); not to be confused with pH. Water does not have to have a low pH to have high acidity. activated carbon Adsorptive particles or granules typically obtained by heating carbonaceous material in the absence of air or insteam and possessing a high capacity to selectively remove trace and soluble components from solution. activated carbon adsorption
Removal of soluble components from aqueous solution by contact
with highly adsorptive granular or powdered carbon. activated sludge Sludge particles produced by the growth of organisms in the aeration tank in the presence of dissolved oxygen. activated-sludge loading The pounds (kilograms) of biochemical oxygen demand in the applied liquid per unit volume of aeration capacity or per kilogram (pound) of activated sludge per day.
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activated-sludge process A biological wastewater treatment process that converts nonsettleable (suspended, dissolved, and colloidal solids) organic materials to a settleable product using aerobic and facultative microorganisms. adsorption The adherence of a gas, liquid, or dissolved material to the surface of a solid or liquid. It should not be confused with absorption. adsorption water
Water held on the surface of solid particles by molecular forces with the
emission of heat (heat of wetting). aeration (1) The bringing about of intimate contact between air and a liquid by one or more of the following methods: (a) spraying the liquid in the air; (b) bubbling air through die liquid; and (c) agitating the liquid to promote surface absorption of air. (2) The supplying of air to confined spaces under nappes, downstream from gates in conduits, and so on to relieve low pressures and to replenish air entrained and removed from such confined spaces by flowing water. (3) Relief of the effects of cavitation by admitting air to the affected section. aerator A device that brings air and a liquid into intimate contact. See diffuser. aerobic
Requiring, or not destroyed by, the presence of free or dissolved oxygen in an aqueous
environment. aerobic bacteria Bacteria that require free elemental oxygen to sustain life. aerosol Colloidal particles dispersed in a gas, smoke, or fog. agglomeration Coalescence of dispersed suspended matter into larger floes or particles. agitator Mechanical apparatus for mixing or aerating. A device for creating turbulence. air diffusion The transfer of air into a liquid through an oxygen-transfer device. See diffusion. algae Photosynthetic microscopic plants that contain chlorophyll that float or are suspended in water. They may also be attached to structures, rocks, and so on. In high concentrations, algae may deplete dissolved oxygen in receiving waters. algal assay
An analytical procedure that uses specified nutrients and algal inoculums to identify
the limiting algal nutrient in waterbodies. alkali Generally, any substance that has highly basic properties; used particularly with reference to the soluble salts of sodium, potassium, calcium, and magnesium. alkaline The condition of water, wastewater, or soil that contains a sufficient amount of alkali substances to raise the pH above 7.0. alkalinity The capacity of water to neutralize acids; a property imparted by carbonates, bicarbonates, hydroxides, and occasionally borates, silicates, and phosphates. It is expressed in calcium carbonate equivalents (mg/L CaC03). alkyl benzene sulfonate (ABS) A type of surfactant, or surface active agent, present in synthetic detergents in the United States prior to 1965. Alkyl benzene sulfonate was troublesome because
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of its foam-producing characteristics and resistance to breakdown by biological action. Alkyl benzene sulfonate has been replaced in detergents by linear alkyl sulfonate, which is biodegradable. alum, aluminum sulfate [AU(SOj)yl8H20] Used as a coagulant in filtration. Dissolved in water, it hydrolyzes into Al(OH)2 and sulfuric acid (H2S04). To precipitate the hydroxide, as needed for coagulation, the water must be alkaline. ambient Generally refers to the prevailing dynamic environmental conditions in a given area. ammonia, ammonium (NH3/ NH?) Urea and proteins are degraded into dissolved ammonia and ammonium in raw wastewaters. Typically, raw wastewater contains 30 to 50 mg/L of NH3. Reactions between chlorine and ammonia are important in disinfection. ammonia-nitrogen The quantity of elemental nitrogen present in the form of ammonia (NH3). amoeba A group of simple protozoans, some of which produce diseases such as dysentery in humans. anaerobic (1) A condition in which free and dissolved oxygen are unavailable. (2) Requiring or not destroyed by the absence of air or free oxygen. anaerobic bacteria Bacteria that grow only in the absence of free and dissolved oxygen. anion A negatively charged ion attracted to the anode under the influence of electrical potential. anionic flocculant A polyelectrolyte with a net negative electrical charge. annual average flow The arithmetic average of all daily flow determinations taken within the preceding 12 consecutive calendar months. The annual average flow determination consists of daily flow volume determinations made by a totalizing meter charted on a chart recorder and limited to significant domestic wastewater discharge facilities with 1 mgd or greater permitted flow. anoxic Condition in which oxygen is available in the combined form only; there is no free oxygen. Anoxic sections in an activated-sludge plant may be used for denitrification. antagonism Detrimental interaction between two entities. See also synergism. antichlors Reagents such as sulfur dioxide, sodium bisulfite, and sodium thiosulfate that can be used to remove excess chlorine residuals from water or watery wastes by conversion to an inert salt. aqueous vapor The gaseous form of water. See water vapor. automatic recording gauge An automatic instrument for measuring and recording graphically and continuously. Also called a register. automatic sampling Collecting of samples of prescribed volume over a defined time period by an apparatus designed to operate remotely without direct manual control. See also composite sample.
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autotrophic organisms Organisms including nitrifying bacteria and algae that use carbon dioxide as a source of carbon for cell synthesis. They can consume dissolved nitrates and ammonium salts. available chlorine A measure of the total oxidizing power of chlorinated lime, hypochlorites, and other materials used as a source of chlorine as compared with that of elemental chlorine. average An arithmetic mean obtained by adding quantities and dividing the sum by the number of quantities. average daily flow (1) The total quantity of liquid tributary to a point divided by the number of days of flow measurement. (2) In water and wastewater applications, the total flow past a point over a period of time divided by the number of days in that period. average flow Arithmetic average of flows measured at a given point. average velocity The average velocity of a stream flowing in a channel or conduit at a given cross section or in a given reach. It is equal to the discharge divided by the cross-sectional area of the section or the average cross-sectional area of the reach. Also called mean velocity. bacteria A group of universally distributed, rigid, essentially unicellular microscopic organisms lacking chlorophyll- They perform a variety of biological treatment processes including biological oxidation, sludge digestion, nitrification, and denitrification. bacterial analysis The examination of water and wastewater to determine the presence, number, and identity of bacteria; more commonly called bacterial examination. bacterial examination The examination of water and wastewater to determine the presence, number, and identity of bacteria. Also called bacterial analysis. See also bacteriological count. bacteriological count A means for quantifying numbers of organisms. See also most probable number. base A compound that dissociates in aqueous solution to yield hydroxy! ions. Beggiatoa A filamentous organism whose growth is stimulated by hydrogen sulfide. bicarbonate alkalinity Alkalinity caused by bicarbonate ions. bioassay (1) An assay method using a change in biological activity as a qualitative or quantitative means of analyzing a material's response to biological treatment. (2) A method of determining the toxic effects of industrial wastes and other wastewaters by using viable organisms; exposure of fish to various levels of a chemical under controlled conditions to determine safe and toxic levels of that chemical. biochemical (1) Pertaining to chemical change resulting from biological action. (2) A chemical compound resulting from fermentation. (3) Pertaining to the chemistry of plant and animal life. biochemical oxidation Oxidation brought about by biological activity resulting in the chemical combination of oxygen with organic matter. See also oxidized wastewater.
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biochemical oxygen demand (BOD) A measure of the quantity of oxygen used in the biochemical oxidation of organic matter in a specified time, at a specific temperature, and under specified conditions. biochemical oxygen demand (BOD) load The BOD content (typically expressed in mass per unit of time) of wastewater passing into a waste treatment system or to a body of water. biofilm Accumulation of microbial growth on the surface of a support material. biological oxidation The process by which living organisms in the presence of oxygen convert organic matter into a more stable or mineral form. biological process (1) The process by which metabolic activities of bacteria and other microorganisms break down complex organic materials into simple, more stable substances. Selfpurification of polluted streams, sludge digestion, and all so-called secondary wastewater treatments depend on this process. (2) Process involving living organisms and their life activities. Also called biochemical process. biomass The mass of biological material contained in a system. biosolids The organic product of municipal wastewater treatment that can be beneficially used. bound water Water held strongly on the surface or in the interior of colloidal particles. (2) Water associated with the hydration of crystalline compounds. breakpoint chlorination Addition of chlorine to water or wastewater until the chlorine demand has been satisfied, with further additions resulting in a residual that is directly proportional to the amount added beyond the breakpoint. brush aerator A surface aerator that rotates about a horizontal shaft with metal blades attached to it; commonly used in oxidation ditches. buffer A substance that resists a change in pH. bulking Inability of activated sludge solids to separate from the liquid under quiescent conditions; may be associated with the growth of filamentous organisms, low dissolved oxygen, or high sludge loading rates. Bulking sludge typically has a sludge volume index > 150 mL/g. butterfly valve A valve in which the disk, as it opens or closes, rotates about a spindle supported by the frame of the valve. The valve is opened at a stem. At full opening, the disk is in a position parallel to the axis of the conduit. calcium carbonate equivalent A common form of expressing hardness, the acidity, or the carbon dioxide, carbonate, bicarbonate, noncarbonate, hydroxide, or total alkalinity of water; expressed in milligrams per liter (mg/L). It is calculated by multiplying the number of chemical equivalents of any of these constituents present in 1 L by 50, the equivalent weight of calcium carbonate. See also chemical equivalent.
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calcium hypochlorite [Ca(OCl)2m4H20] A solid that, when mixed with water, liberates the hypochlorite ion OC1" and can be used for disinfection. calibration (1) The determination, checking, or rectifying of the graduation of any instrument giving quantitative measurements. (2) The process of taking measurements or of making observations to establish the relationship between two quantities. calorie The amount of heat necessary to raise the temperature of 1 g of water at 15 째C by 1 째C. carbon (C) (1) A chemical element essential for growth. (2) A solid material used for adsorption of pollutants. carbonaceous biochemical oxygen demand (CBOD) A quantitative measure of the amount of dissolved oxygen required for the biological oxidation of carbon-containing compounds in a sample. See also biochemical oxygen demand. carbon adsorption The use of either granular or powdered carbon to remove organic compounds from wastewater or effluents. Organic molecules in solution are drawn to the highly porous surface of the carbon by intermolecular attraction forces. carbonate hardness Hardness caused by the presence of carbonates and bicar-bonates of calcium and magnesium in water. Such hardness may be removed to the limit of solubility by boiling the water. When the hardness is numerically greater than the sum of the carbonate alkalinity and bicarbonate alkalinity, the amount of hardness is equivalent to the total alkalinity and-is called carbonate hardness. It is expressed in milligrams of equivalent calcium carbonate per. liter (mg/L CaCOs), See also hardness. carbonatiou The diffusion of carbon dioxide gas through a liquid to render the liquid stable with respect to precipitation or dissolution of alkaline constituents. See also recarbonation. carcinogen A material that induces excessive or abnormal cellular growth in an organism. carrying capacity The maximum rale of flow that a conduit, channel, or other hydraulic structure is capable of passing. cascade aerator An aerating device built in the form of steps or an inclined plane on which are placed staggered projections arranged to break up the water and bring it into contact with air. cation A positively charged ion attracted to the cathode under the influence of electrical potential. cationic flocculant A polyelectrolyte with a net positive electrical charge. caustic alkalinity The alkalinity caused by hydroxy! ions. See also alkalinity. CBOD Carbonaceous biochemical oxygen demand. CBOD5 Five-day carbonaceous biochemical oxygen demand. Celsius The international name for the centigrade scale of temperature, on which the freezing point and boiling point of water are 0 째C and 100 째C, respectively, at normal atmospheric pressure.
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centigrade A thermometer temperature scale in which 0째 marks the freezing point and 100째 the boiling point of water at 760-mm Hg barometric pressure. Also called Celsius. To convert temperature on this scale to Fahrenheit, multiply by 1.8 and add 32. centrifugation Imposition of a centrifugal force to separate solids from liquids based on density differences. In sludge dewatering, the separated solids are commonly called cake and the liquid is called centrate. centrifuge A mechanical device in which centrifugal force is used to separate solids from liquids or to separate liquids of different densities. certification A program to substantiate the capabilities of personnel by documentation of experience and learning in a defined area of endeavor. change of state The process by which a substance passes from one to another of the solid, the liquid, and the gaseous states, and in which marked changes in its physical properties and molecular structure occur. chemical coagulation The destabilization and initial aggregation of colloidal and finely divided suspended matter by the addition of an inorganic coagulant. See also flocculation. chemical conditioning Mixing chemicals with a sludge prior to dewatering to improve solids separation characteristics. Typical conditioners include polyelec-trolytes, iron salts, and lime. chemical dose A specific quantity of chemical applied to a specific quantity of fluid for a specific purpose. chemical equilibrium The condition that exists when there is no net transfer of mass or energy between the components of a system. This is the condition in a reversible chemical reaction when the rate of the forward reaction equals the rate of the reverse reaction. chemical equivalent The weight (in grams) of a substance that combines with or displaces 1 g of hydrogen. It is found by dividing the formula weight by its valence. chemical oxidation The oxidation of compounds in wastewater or water by chemical means. Typical oxidants include ozone, chlorine, and potassium permanganate. chemical oxygen demand (COO) A quantitative measure of the amount of oxygen required for the chemical oxidation of carbonaceous (organic) material in wastewater using inorganic dichromate or permanganate salts as oxidants in a 2-hour test. chemical precipitation (1) Formation of particulates by the addition of chemicals. (2) The process of softening water by the addition of lime or lime and soda to form insoluble compounds; typically followed by sedimentation or filtration to remove newly created suspended solids. chemical reaction A transformation of one or more chemical species into other species resulting in the evolution of heat or gas, color formation, or precipitation. It may be initiated by a physical process such as heating, by die addition of a chemical reagent, or it may occur spontaneously.
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chemical reagent A chemical added to a system to induce a chemical reaction. chemical treatment Any treatment process involving the addition of chemicals to obtain a desired result such as precipitation, coagulation, flocculation, sludge conditioning, disinfection, or odor control. chloramines "Compounds of organic or inorganic nitrogen formed during the addition of chlorine to wastewater. See also breakpoint chlorination. chlorination The application of chlorine or chlorine compounds to water or wastewater, generally for the purpose of disinfection, but frequently for chemical oxidation and odor control. chloriitator Any metering device used to add chlorine to water or wastewater. chlorine (CU) An element ordinarily existing as a greenish-yellow gas about 2.5 times heavier than air. At atmospheric pressure and a temperature of 30.1 째F (>48 째C), the gas becomes an amber liquid about 1.5 times heavier than water. Its atomic weight is35.457 and its molecular weight is 70.914. chlorine demand The difference between the amount of chlorine added to wastewater and the amount of chlorine remaining after a given contact time. Chlorine dosage is a function of the substances present in water, temperature, and contact time. chlorine dose The amount of chlorine applied to a wastewater, typically expressed in milligrams per liter (mg/L). chlorine residual The amount of chlorine in all forms remaining in water after treatment to ensure disinfection for a period of time. chlorine toxicity The detrimental effects on biota caused by the inherent properties of chlorine. chromatography The generic name of a group of separation processes that depend on the redistribution of the molecules of a mixture between a gas or liquid phase in contact with one or more bulk phases. The types of chromatography are adsorption, column, gas, gel, liquid, thinlayer, and paper. ciliated protozoa Protozoans with cilia (hair-like appendages) that assist in movement; common in trickling filters and healthy activated sludge. Free-swimming ciliates are present in bulk liquid; stalked ciliates are commonly attached to solids matter in the liquid. coagulant A simple electrolyte, typically an inorganic salt containing a multivalent cation of iron, aluminum, or calcium [e.g., FeCl> FeCl2, Al2 (SO..)-,, and CaO]. Also, an inorganic acid or base that induces coagulation of suspended solids. See also flocculant. coagulant or flocculant aid An insoluble particulate used to enhance solid-liquid separation by providing nucleating sites or acting as a weighting agent or sorbent; also used colloquially to describe the action of flocculents in water treatment.
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coagulation The conversion of colloidal (<0.001 mm) or dispersed (0.001 to 0.1 mm) particles into small visible coagulated particles (0.1 to 1 mm) by the addition of a coagulant, compressing the electrical double layer surrounding each suspended particle, decreasing the magnitude of repulsive electrostatic interactions between particles, and thereby destabilizing the particle. See also floccu hit ion. coagulation basin A basin used for the coagulation of suspended or colloidal matter, with or without the addition of a coagulant, in which the liquid is mixed gently to induce agglomeration with a consequent increase in the settling velocity of particulates. Cocci Sphere-shaped bacteria. cudisposal Joint disposal of wastewater sludge and municipal refuse in one process or facility. Disposal can be intermediate, as with incineration or composting, or final, as with placement in a sanitary landfill. coefficient A numerical quantity, determined by experimental or analytical methods, interposed in a formula that expresses the relationship between two or more variables to include the effect of special conditions or to correct a theoretical relationship to one found by experiment or actual practice. cohesion
The force of molecular attraction between the particles of any substance that tends to
hold them together. colifarm-group bacteria A group of bacteria predominantly inhabiting the intestines of man or animal, but also occasionally found elsewhere. It includes all aerobic and facultative anaerobic, gram-negative, non-spore-forming, rod-shaped bacteria that ferment lactose with the production of gas. Also included are all bacteria that produce a dark, purplish-green metallic sheen by the membrane filter technique used for coliform identification. The two groups are not always identified, but they are generally of equal sanitary significance. colloids Finely divided solids (less than 0.002 mm and greater than 0.000 001 mm) that will not settle but may be removed by coagulation, biochemical action, or membrane filtration; they are intermediate between true solutions and suspensions. colony
A discrete clump of microorganisms on a surface as opposed to dispersed growth
throughout a liquid culture medium. color Any dissolved solids that impart a visible hue to water. colorimeter
An instrument that quantitatively measures the amount of light of a specific
wavelength absorbed by a solution. combined available chlorine The concentration of chlorine that is combined with ammonia as chloramine or as other chloro derivatives, yet is still available to oxidize organic matter.
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combined available residual chlorine That portion of the total residual chlorine remaining in water or wastewater at the end of a specified contact period that will react chemically and biologically as chloramines. combined residual chlorination The application of chlorine to water or wastewater to produce, with natural or added ammonia or with certain organic nitrogen compounds, a combined chlorine residual. combustible-gas indicator An explosimeter; a device for measuring die concentration of potentially explosive fumes. The measurement is based on the catalytic oxidation of a combustible gas on a heated platinum filament that is part of a Whetstone bridge. composite sample A composite sample for domestic wastewater is a sample made up of a minimum of three effluent portions collected in a continuous 24-hour period or during the period of daily discharge if it is less than 24 hours, combined in volumes proportional to flow, and collected no closer than 2 hours apart. For industrial wastewater, a composite sample is a sample made up of a minimum of three effluent portions collected in a continuous 24-hour period or during the period of daily discharge if it is less than 24 hours, combined in volumes proportional to flow, and collected no closer than 1 hour apart. concentration (1) The amount of a given substance dissolved in a discrete unit volume of solution or applied to a unit weight of solid. (2) The process of increasing the dissolved solids per unit volume of solution, typically by evaporation of the liquid. (3) The process of increasing the suspended solids per unit volume of sludge as by sedimentation or dewatering. concentrator A solids contact unit used to decrease the water content of sludge or slurry. condensation The process by which a substance changes from the vapor state to the liquid or solid state. Water that falls as precipitation from the atmosphere has condensed from the vapor state to rain or snow. Dew and frost are also forms of condensation. condenser Any device for reducing gases or vapors to liquid or solid form. contact time The time that the material processed is exposed to another substance (such as activated sludge or activated carbon) for completion of the desired reaction. See also detention time. correlation (1) A mutual relationship or connection. (2) The degree of relative correspondence, as between two sets of data. culture Any organic growth that has been developed intentionally by providing suitable nutrients and environment. culture media Substances used to support the growth of microorganisms in analytical procedures. daily average flow The arithmetic average of all determinations of the daily discharge within a period on one calendar month. The daily average flow determination consists of determinations
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made on at least four separate days. If instantaneous measurements are used to determine the daily discharge, the determination is the arithmetic average of all instantaneous measurements taken during that month. Daily average flow determination for intermittent discharges consists of a minimum of three flow determinations on days of discharg'e.' Basic Laboratory Procedures for the Operator-Analyst daily maximum concentration The maximum concentration measured on a single day, by composite sample unless otherwise specified in the permit, within a period of one calendar month. daily maximum flow The highest total flow for any 24-hour period in a calendar month. data Records of observations and measurements of physical facts, occurrences, and conditions reduced to written, graphical, or tabular form. decantation ' Separation of a liquid from solids or from a liquid of higher density by drawing off the upper layer after the heavier material has settled. dechlorination The partial or complete reduction of residual chlorine by any chemical or physical process. Sulfur dioxide is frequently used for this purpose. declining growth phase Period of time between the log-growth phase and the endogenous phase, where the amount of food is in short supply, leading to ever-slowing bacterial growth rates. degree (1) On the centigrade or Celsius thermometer scale, 1/100 of the interval from the freezing point to the boiling point of water under standard conditions; on the Fahrenheit scale, 1/180 of this interval. (2) A unit of angular measure; the central angle subtended by 1/360 of the circumference of a circle. design flow Engineering guidelines that typically specify the amount of influent flow that can be expected on a daily basis over the course of a year. Other design flows can be set for monthly or peak flows. design loadings Flowrates and constituent concentrations that determine the design of a process unit or facility necessary for prop>er operation. detergent (1) Any of a group of synthetic, organic, liquid, or water-soluble cleaning agents that are inactivated by hard water and have wetting and emulsifying properties but, unlike soap, are not prepared from fats and oils. (2) A substance that reduces the surface tension of water. dewpoint The temperature to which air with a given concentration of water vapor must be cooled to cause condensation of the vapor. dijfuser A porous plate, tube, or other device through which air is forced and divided into minute bubbles for diffusion in liquids. In the activated sludge process, it is a device for dissolving air into mixed liquor. It is also used to mix chemicals such as chlorine through perforated holes. diffusion (1) The transfer of mass from one fluid phase to another across an interface, for example, liquid to solid or gas to liquid. (2) The spatial equalization of one material throughout another.
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digested solids Solids digested under either aerobic or anaerobic conditions until the volatile content has been reduced to the point at which the solids are relatively nonpulrescible and inoffensive. digestion The biological decomposition of organic matter in sludge, resulting in partial liquefaction, mineralization, and volume reduction. discharge monitoring report (DMR) The discharge monitoring report (U.S. Environmental Protection Agency Form 3320-1) is a form completed by a National Pollutant Discharge Elimination System permitee that documents the required sample collection and analytical results. discharge rate (1) Determination of the quantity of water flowing per unit of time in a stream channel, conduit, or orifice at a given point by means of a current meter, rod float, weir, pitot tube, or other measuring device or method. The operation includes not only the measurement of velocity of water and the cross-sectional area of the stream of water, but also the necessary subsequent computations. (2) The numerical results of a measurement of discharge, expressed in appropriate units. disinfection (Î&#x160;) The killing of waterborne fecal and pathogenic bacteria and viruses in potable water supplies or wastewater effluents with a disinfectant; an operational term that must be defined within limits, such as achieving an effluent with no more than 200 colonies of fecal coli form/100 mL. (2) The killing of the larger portion of microorganisms, excluding bacterial spores, in or on a substance with the probability that all pathogenic forms are killed, inactivated, or otherwise rendered nonvirulent. dissolved oxygen The oxygen dissolved in liquid, typically expressed in milligrams per liter (mg/L) or percent saturation. dissolved solids Solids in solution that cannot be removed by filtration; for example, sodium chloride (NaCl) and other salts that must be removed by evaporation. See also total dissolved solids. DPD method An analytical method for determining chlorine residual using the reagent n-diethyl-pphenylenediamine (DPD). This is the most commonly and officially recognized test for free chlorine residual. dry-bulb temperature The temperature of air measured by a conventional thermometer. dry suspended solids The weight of the suspended matter in a sample after drying for a specified time at a specific temperature. dry weather flow (1) The flow of wastewater in a combined sewer during dry weather. Such flow consists mainly of wastewater, with no stormwater included. (2) The flow of water in a stream during dry weather, typically contributed entirely by groundwater. E. coli See Escherichia coli.
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effective size The diameter of the particles, spherical in shape, equal in size, and arranged in a given manner, of a hypothetical sample of granular'material that would have the same transmission constant as the actual material under consideration. There are a number of methods for determining effective size, the most common being that developed by Allen Hazen, which consists of passing the granular material through sieves with varying dimensions of mesh. In this method, the effective size is determined from the dimensions of that mesh, which permits 10% of the sample to pass and will retain the remaining 90%; in other words, the effective size is that for which 10% of the grains are smaller and 90% larger. effluent Wastewater or other liquid, partially or completely treated or in its natural state, flowing out of a reservoir, basin, treatment plant, or industrial treatment plant, or part thereof. emulsifying agent An agent capable of modifying the surface tension of emulsion droplets to prevent coalescence. Examples are soap and other surface-active agents, certain proteins and gums, water-soluble cellulose derivatives, and poly-hydric alcohol esters and ethers. emulsion A heterogeneous liquid mixture of two or more liquids not typically dissolved in one another, but held in suspension one in the other by forceful agitation or emulsifiers that modify the surface tension of the droplets to prevent coalescence. endogenous respiration Autooxidation by organisms in biological processes. Enterococci A group of Cocci that typically inhabit the intestines of man and animals. Incorrectly used interchangeably with fecal Streptococci. enzyme A catalyst produced by living cells. All enzymes are proteins, but not all proteins are enzymes. equilibrium A condition of balance in which the rate of formation and the rate of consumption or degradation of various constituents are equal. See also chemical equilibrium. Escherichia coli (E. coli) One of the species of bacteria in the fecal coliform group. It is found in large numbers in the gastrointestinal tract and feces of warm-blooded animals and man. Its presence is considered indicative of fresh fecal contamination and it is used as an indicator organism for the presence of less easily detected pathogenic bacteria. extraction The process of dissolving and separating out particular constituents of a liquid by treatment with solvents specific for those constituents. Extraction maybe liquid-solid or liquid-liquid. faadtative bacteria Bacteria that can grow and metabolize in the presence or absence of dissolved oxygen. Fahrenheit A temperature scale in which 32째 marks the freezing point and 212째 the boiling point of water at 760-mm Hg. To convert to centigrade (Celsius), subtract 32 and multiply by 0.5556. fats (wastes) Triglyceride esters of fatty acids; erroneously used as a synonym for grease.
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fecal coliform Aerobic and facultative, gram-negative, non-spore-forming, rod-shaped bacteria capable of growth at 44.5 °C (112 °F), and associated with fecal matter of warm-blooded animals. fecal coliform bacteria concentration The number of colonies of fecal coliform bacteria per 100 mL of effluent. The fecal coliform bacteria daily average is a geometric mean of the values for the effluent samples collected in a calendar month. The geometric mean is determined by calculating the "nth" root of the product of all measurements made in a particular period of time. For example in a month's time, where η equals the number of measurements made, or, computed as the antilogarithm of the arithmetic average of the logarithms of each measurement made. For any measurement of fecal coliform bacteria equaling zero, a substituted value of one shall be made for input into either computation method. fecal indicators Fecal coliform, fecal Streptococci, and other bacterial groups originating in human or other warm-blooded animals, indicating contamination by fecal matter. fecal Streptococci The subgroup of Enterococci that is of particular concern in water and wastewater. See also Enterococci. ferric chloride (FeCl3) A soluble iron salt often used as a sludge conditioner to enhance precipitation or bind up sulfur compounds in wastewater treatment. See also coagulant. ferric sulfate [Fe2 (SO.,)3] A water-soluble iron salt formed by the reaction of ferric hydroxide and sulfuric acid or by the reaction of iron and hot concentrated sulfuric acid; also obtainable in solution by the reaction of chlorine and ferrous sulfate; used in conjunction with lime as a sludge conditioner to enhance precipitation. ferrous chloride (FeCl2) A soluble iron salt used as a sludge conditioner to enhance precipitation or bind up sulfur. See also coagulaid. ferrous sulfate (FeSO.t-7H20) A water-soluble iron salt, sometimes called copperas; used in conjunction with lime as a sludge conditioner to enhance precipitation. filamentous growtli Intertwined, thread-like biological growths characteristic of some species of bacteria, fungi, and algae. Such growths reduce sludge set-tleability and dewaterability. filamentous organisms Bacterial, fungal, and algal species that grow in threadlike colonies resulting in a biological mass that will not settle and may interfere with drainage through, a filter. filtrate Liquid that has passed through a filter. final effluent The effluent from the final treatment unit of a wastewater treatment plant. first-stage biochemical oxygen demand That part of oxygen demand associated with biochemical oxidation of carbonaceous material. Typically, the greater part of the carbonaceous material is oxidized before the second stage (active oxidation of the nitrogenous material) takes place.
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five-day biochemical oxygen demand (BOD-,) A standard test to assess wastewater pollution caused by organic substances, measuring the oxygen used under controlled conditions of temperature (20 째C) and time (5 days). fixed solids The residue remaining after ignition of suspended or dissolved matter. //oc Collections of smaller particles agglomerated into larger, more easily settleable particles through chemical, physical, or biological treatment. See also flocculation. Flocculant water-soluble organic polyelectrolytes that are used alone or in conjunction with inorganic coagulants, such as aluminum or iron salts, to agglomerate the solids present to form large, dense floe particles that settle rapidly. flocculation In water and wastewater treatment, the agglomeration of colloidal and finely divided suspended matter after coagulation by gentle stirring by either mechanical or hydraulic means. For biological wastewater treatment in which coagulation is not used, agglomeration may be accomplished biologically. flocculation agent A coagulating substance that, when added to water, forms a flocculent precipitate that will entrain suspended matter and expedite sedimentation; examples are alum, ferrous sulfate, and lime. flushing The flow of water under pressure in a conduit or well to remove clogged material. food-to-niicroorganism ratio (F:M) In the activated sludge process, the loading rate expressed as kilograms (pounds) of BOD5 per kilogram (pound) of mixed liquor or mixed liquor volatile suspended solids per day. formazin turbidity unit (FTU) A standard unit of turbidity based on a known chemical reaction that produces insoluble particulates of uniform size. The FTU has largely replaced the Jackson turbidity unit. Also known as nephelometric turbidity unit. free available chlorine The amount of chlorine available as dissolved gas, hypochlorous acid, or hypochlorite ion that is not combined with an amine or other organic compound. free available residual chlorine That portion of the total residual chlorine remaining in water or wastewater at the end of a specified contact period that will react chemically and biologically as hypochlorous acid or hypochlorite ion. free oxygen Elemental oxygen (02). free-swimming ciliate Mobile, one-celled organisms using cilia (hair-like projections) for movement. free water Suspended water constituting films covering the surface of solid particles or the walls of fractures, but in excess of pellicular water; mobile water is free to move in any direction under the pull of the force of gravity and unbalanced film pressure. fungi Small, nonchlorophyll-bearing plants that lack roots, stems, or leaves; occur (among other places) in water, wastewater, or wastewater effluents; and grow best in the absence of light. Their
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decomposition may cause disagreeable tastes and odors in water; in some wastewater treatment processes they are helpful and in others they are detrimental. gas chromatography A method of separating a mixture of compounds into its constituents so they can be identified. The sample is vaporized into a gas-filled column, fractionated by being swept over a solid adsorbent, selectively eluted, and identified. gas chromatography-mass spectrometry (GC-MS) An analytical technique involving the use of both gas chromatography and mass spectrometry, the former to separate a complex mixture into its components and the latter to deduce the atomic and molecular weights of those components. It is particularly useful in identifying organic compounds. grab sample A sample taken at a given place and time. It may be representative of the flow. gradient The rate of change of any characteristic per unit of length or slope. The term is typically applied to such things as elevation, velocity, or pressure. See also slope. grease and oil In wastewater, a group of substances including fats, waxes, free fatty acids, calcium and magnesium soaps, mineral oils, and certain other non-fatty materials; water-insoluble organic compounds of plant and animal origins or industrial wastes that can be removed by natural flotation skimming. hardness A characteristic of water imparted primarily by salts of calcium and magnesium, such as bicarbonates, carbonates, sulfates, chlorides, and nitrates, that causes curdling and increased consumption of soap, deposition of scale in boilers, damage in some industrial processes, arid sometimes objectionable taste. It may be determined by a standard laboratory titration procedure or computed from the amounts of calcium and magnesium expressed as calcium carbonate equivalents. See also carbonate hardness. heavy metals Metals of relatively high density or high molecular weight that can be precipitated byhydrogen sulfide in acid solution, for example, lead, silver, gold, mercury, bismuth, and copper. hydrogen sulfide (H2S) A toxic and lethal gas produced in sewers and digesters by anaerobic decomposition. Detectable in low concentrations (%) by its characteristic "rotten egg" odor. It deadens the sense of smell in higher concentrations or after prolonged exposure. Respiratory paralysis and death may occur quickly at concentrations as low as 0.07% by volume in air. liypochlorination
The use of sodium hypochlorite (NaOC12) for disinfection. hypochlorite
Calcium, sodium, or lithium hypochlorite. index (1) An indicator, typically numerically expressed, of the relation of one phenomenon to another. (2) An indicating part of an instrument. indicator (1) A device that shows by art index, pointer, or dial the instantaneous value of such quantities as depth, pressure, velocity, stage, or the movements or positions of water-controlling
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devices; a gauge (see also recorder). (2) A substance giving a visible change, typically of color, at a desired point in a chemical reaction, generally at a prescribed endpoinl. inorganic All those combinations of elements that do not include organic carbon. inorganic matter Mineral-type compounds that are generally nonvolatile, not combustible, and not biodegradable. Most inorganic-type compounds or reactions are ionic in nature; therefore, rapid reactions are characteristic. ion A charged atom, molecule, or radical that affects the transport of electricity through an electrolyte or, to a certain extent, through a gas. An atom or molecule that has lost or gained one or more electrons. ion excliange (1) A chemical process involving reversible interchange of ions between a liquid and a solid, but no radical change in structure of the solid. (2) A chemical process in which ions from two different molecules are exchanged. (3) The reversible transfer or sorption of ions from a liquid to a solid phase by replacement with other ions from the solid to the liquid. See also regeneration. Jackson turbidity unit (JTU) A standard unit of turbidity based on the visual extinction of a candle flame when viewed through a column of turbid water containing suspended solids. It varies with the solids composition (barium sulfate, diatomaceous earth, and so on). The JTU has largely been replaced by the more reproducible nephelometric turbidity unit. jar test A laboratory procedure for evaluating coagulation, flocculation, and sedimentation processes in a series of parallel comparisons. laboratory procedures Modes of conducting laboratory processes and analytical tests consistent with validated standard testing techniques. lag growth phase The initial period following bacterial introduction during which the population grows slowly as the bacteria acclimates to the new environment. lethal concentration The concentration of a test material that causes death of a specified percentage of a population, typically expressed as the median or 50% level (L50). lipids A group of organic compounds that make up the fats and other esters with analogous properties. liquid .A substance that flows freely; characterized by free movement of the constituent molecules among themselves, but without the tendency to separate from one another, which is characteristic of gases. Liquid and fluid are often used synonymously, but fluid has the broader.significance of including both liquids and gases. log growth phase Initial stage of bacterial growth, during which there is an ample food supply, causing bacteria to grow at their maximum rate.
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mass spectrometer A device that permits observation of the masses of molecular fragments produced by destructible bombardment of the molecule with electrons in a vacuum; coupled with gas chromatography and mass spectrometry, it can yield specific compound identification. mass spectrometry A means of sorting ions by separating them according to their masses. maximum 2-hour peak flow Applies to domestic wastewater treatment plants: the highest 2-hour peak flow for any 24-hour period in a calendar month. mean (1) The arithmetic average of a group of data. (2) The statistical average (50% point) determined by probability analysis. mean cell residence time (MCRT) The average time that a given unit of cell mass stays in the activated sludge aeration tank. It is typically calculated as the total mixed liquor suspended solids in the aeration tank divided by the combination of solids In the effluent and solids wasted. median In a statistical array, the value having as many cases larger in value as cases smaller in value. membrane filter test A sample of water is passed through a sterile filter membrane. The filter is removed and placed on a culture medium and then incubated for a preset period of time. Coliform colonies, which have a pink to dark-red color with a metallic sheen, are then counted using the aid of a low-power binocular wide-field dissecting microscope. The membrane filter test is used to test for the presence and relative number of coliform organisms. mercaptaus Aliphatic organic compounds that contain sulfur. They are noted for their disagreeable odor and are found in certain industrial wastes. mesh One of the openings or spaces in a screen. The value of the mesh is typically given as the number of openings per linear centimeter (inch). This'gives no recognition to the diameter of the wire; thus, the mesh number does not always have a definite relationship to the size of the hole. mesophilic range Operationally, that temperature range most conducive to the maintenance of optimum digestion by mesophilic bacteria, generally accepted as between 27 and 38 째C (80 and 100 째F). metabolism (1) The biochemical processes in which food is used and wastes formed by living organisms. (2) All biochemical reactions involved in cell synthesis and growth. metazoan A group of animals having bodies composed of cells differentiated into tissues and organs and typically having a digestive cavity lined with specialized cells. meter An instrument for measuring some quantity such as the rate of flow of liquids, gases, or electric currents. microbial activity The activities of microorganisms resulting in chemical or physical changes. microorganisms Very small organisms, either plant or animal, invisible or barely visible to the naked eye. Examples are algae, bacteria, fungi, protozoa, and viruses.
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microscopic Very small, generally between 0.5 and 100 mm, and visible only by magnification with an optical microscope. microscopic examination (1) The examination of water to determine the presence and amounts of plant and animal life, such as bacteria, algae, diatoms, protozoa, and Crustacea. (2) The examination of water to determine the presence of microscopic solids. (3) The examination of microbiota in process water, such as mixed liquor in an activated sludge plant. mixed liquor A mixture of raw or settled wastewater and activated sludge contained in an aeration tank in the activated sludge process. See also mixed liquor suspended solids. mixed liquor suspended solids (MLSS) The concentration of suspended solids in activated sludge mixed liquor, expressed in milligrams per liter (mg/L). Commonly used in connection with activated sludge aeration units. mixed liquor volatile suspended solids (MLVSS) That fraction of the suspended solids in activated sludge mixed liquor that can be driven off by combustion at 550 째C (1022 째F); it indicates the concentration of microorganisms available for biological oxidation. mole (1) Molecular weight of a substance, typically expressed in grams. (2) A device to clear sewers and pipelines. (3) A massive harbor work, with a core of earth or stone, extending from shore into deep water. It serves as a breakwater, a berthing facility, or a combination of the two. monitoring (1) Routine observation, sampling, and testing of designated locations or parameters to determine the efficiency of treatment or compliance with standards or requirements. (2) The procedure or operation of locating and measuring radioactive contamination by means of survey instruments that can detect and measure, as dose rate, ionizing radiations. Monod equation A mathematical expression first used by Monod in describing the relationship between the microbial growth rate and concentration of growth-limiting substrate. most probable number (MPN) That number of organisms per unit volume which, in accordance with statistical theory, would be more likely than any other number to yield the observed test result or would yield the observed test result with the greatest frequency. Expressed as density of organisms/100 mL. Results are computed from the number of positive findings of coliform group organisms resulting from multiple portion decimal dilution plantings. Commonly used for coliform bacteria. moving average Trend analysis tool for determining patterns or changes in treatment process. For example, a 7-day moving average would be the sum of the datum points for 7 days divided by 7. National Pollutant Discharge Elimination System (NPDES) A permit that is the basis for the monthly monitoring reports required by most states in the United States. nematode Member of the phylum (Nematoda) of elongated cylindrical worms parasitic in animals or plants or free-living in soil or water.
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nephelometer An instrument for comparing turbidities of solutions by passing a beam of light through a transparent tube and measuring the ratio of the intensity of the shattered light to that of the incident light. nephelometric turbidity unit (NTU) Units of a turbidity measurement using a nephelometer. nitrate (N03) An oxygenated form of nitrogen. nitrifying bacteria Bacteria capable of oxidizing nitrogenous material. nitrite (N02) An intermediate oxygenated form of nitrogen. nitrogen (Nj An essential nutrient that is often present in wastewater as ammonia. nitrate, nitrite, and organic nitrogen The concentrations of each form and the sum (total nitrogen) are expressed as milligrams per liter (mg/L) elemental nitrogen. Also present in some groundwater as nitrate and in some polluted groundwater in other forms. See also nutrient. Nitrobacter A genus of bacteria that oxidize nitrite to nitrate. Basic Laboratory Procedures for the Operator-Analyst nitrogen cycle A graphical presentation of the conservation of matter in nature showing the chemical transformation of nitrogen through various stages of decomposition and assimilation. The various chemical forms of nitrogen as they move among living and nonliving matter are used to illustrate general biological principles that are applicable to wastewater and sludge treatment. nitrogenous oxygen demand (NOD) A quantitative measure of the amount of oxygen required for the biological oxidation of nitrogenous material, such as ammonia-nitrogen and organic nitrogen, in wastewater; typically measured after the carbonaceous oxygen demand has been satisfied. See also biochemical oxygen demand, nitrification, and second-stage BOD. Nitrosomonas A genus of bacteria that oxidize ammonia to nitrite. Nocardia Irregularly bent, short filamentous organisms that are characterized in an activated sludge system when a dark chocolate mousse foam is present. nonsettleablc solids Suspended matter that will stay in suspension for an extended period of time. Such a period may be arbitrarily taken for testing purposes as 1 hour. See also suspended solids. nutrient Any substance that is assimilated by organisms and promotes growth; generally applied to nitrogen and phosphorus in wastewater, but also to other essential and trace elements. organic Refers to volatile, combustible, and sometimes biodegradable chemical compounds containing carbon atoms (carbonaceous) bonded together with other elements. The principal groups of organic substances found in wastewater are proteins, carbohydrates, and fats and oils. See also inorganic. organic loading The amount of organic material, typically measured as 5-day biochemical oxygen demand, applied to a given treatment process; expressed as weight per unit time per unit surface area or per unit weight.
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organic nitrogen Nitrogen chemically bound in organic molecules such as proteins, amines, and amino acids. orthophosphate (1) A salt that contains phosphorus as (PO*.)- . (2) A product of hydrolysis of condensed (polymeric) phosphates. (3) A nutrient required for plant and animal growth. See also nutrient and phosphorus removal. osmosis The process of diffusion of a solvent through a semipermeable membrane from a solution of lower concentration to one of higher concentration. outfall (1) The point, location, or structure where wastewater or drainage discharges from a sewer, drain, or other conduit. (2) The conduit leading to the ultimate disposal area. oxidant A chemical substance capable of promoting oxidation, for example, 02, 03, and Cl2. See also oxidation and reduction. oxidation (1) A chemical reaction in which the oxidation number (valence) of an element increases because of the loss of one or more electrons by that element. Oxidation of an element is accompanied by simultaneous reduction of the other reactant. See also reduction. (2) The conversion or organic materials to simpler, more stable forms with the release of energy. This may be accomplished by chemical or biological means. (3) The addition of oxygen to a compound. oxidation-reduction potential (ORP) The potential required to transfer electrons from the oxidant to the reductant; used as a qualitative measure of the state of oxidation in wastewater treatment systems. oxygen (O) A necessary chemical element. Typically found as 02 and used in biological oxidation. It constitutes approximately 20% of the atmosphere. oxygen transfer (1) Exchange of oxygen between a gaseous and a liquid phase. (2) The amount of oxygen absorbed by a liquid compared to the amount fed into the liquid through an aeration or oxygenation device; typically expressed as percent. oxygen uptake rate The oxygen used during biochemical oxidation, typically expressed as mg 02/L/h in the activated sludge process. ozone (03) Oxygen in a molecular form with three atoms of oxygen forming each molecule. partial pressure The pressure exerted by each gas independently of the others in a mixture of gases. The partial pressure of each gas is proportional to the amount (percent by volume) of that gas in the mixture. particles Generally, discrete solids suspended in water or wastewater that can vary widely in size, shape, density, and charge. parts per million (ppm) The number of weight or volume units of a minor constituent present with each 1 million units of a solution or mixture. The more specific term, milligrams per liter (mg/L), is preferred.
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pcnneability (1) The properly of a material that permits appreciable movement of water through it when it is saturated; the movement is actuated by hydrostatic pressure of the magnitude typically encountered in natural subsurface water. Perviousness is sometimes used in the same sense as permeability. (2) The capacity of a rock or rock material to transmit a fluid. See also permeability coefficient. permeability coefficient A coefficient expressing the rate of flow of a fluid through a cross section of permeable material under a hydraulic or pressure gradient. The standard coefficient of permeability used in the hydrologic work of the U.S. Geological Survey, known also as the Meinzer unit, is defined as the rate of flow of water in liters per second (gallons per day) at 60 °F through a '"·' cross section of 1 ft (0.3 m) under a hydraulic gradient of 100%. See also field permeability coefficiei11. pH A measure of the hydrogen-ion concentration in a solution, expressed as the logarithm (base 10) of the reciprocal of the hydrogen-ion concentration in gram moles per liter (g/mol/L). On the pH scale (0 to 14), a value of 7 at 25 °C (77 °F) represents a neutral condition. Decreasing values indicate increasing hydrogen-ion concentration (acidity); increasing values indicate decreasing hydrogen-ion concentration (alkalinity). phenolic compounds Hydroxyl derivatives of benzene. The simplest phenolic compound ishydroxyl benzene (C(1HsOH). phosphate A salt or ester of phosphoric acid. See also orthophosphate and phosphorus. phosphorus An essential chemical element and nutrient for all life forms. Occurs in orthophosphate, pyrophosphate, tripolyphosphate, and organic phosphate forms. Each of these forms and their sum (total phosphorus) is expressed as milligrams per liter (mg/L) elemental phosphorus. See also nutrient. photosynthesis The synthesis of complex organic materials, especially carbohydrates, from carbon dioxide, water, and inorganic salts with sunlight as the source of energy and with the aid of a catalyst, such as chlorophyll. photosynthetic bacteria Bacteria that obtain their energy for growth from light by photosynthesis. physical analysis The examination of water and wastewater to determine physical characteristics such as temperature, turbidity, color, odors, and taste. physical-chemical treatment Treatment of wastewater by unit processes other than those based on microbiological activity. Unit processes commonly included are precipitation with coagulants, flocculation with or without chemical floccu-lents, filtration, adsorption, chemical oxidation, air stripping, ion exchange, reverse osmosis, and several others.
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physical treatment Any treatment process involving only physical means of solid-liquid separation/ for example, screens, racks, clarification, and com-minutors. Chemical and biological reactions do not play an important role in treatment. phytoplankton Plankton consisting of plants such as algae. polychlorinated biphcnyls (PCBs) A class of aromatic organic compounds with two six-carbon unsaturated rings, with chlorine atoms substituted on each ring and more than two such chlorine atoms per molecule of PCB. They are typically stable, resist both chemical and biological degradation, and are toxic to many biological species. polyelectrolyte flocculants Polymeric organic compounds used to induce or enhance the flocculation of suspended and colloidal solids and thereby facilitate sedimentation or the dewatering of sludges. poly electrolytes Complex polymeric compounds, typically composed of synthetic macromolecules that form charged species (ions) in solution; water-soluble polyelectrolytes are used as flocculants; insoluble polyelectrolytes are used as ion exchange resins. See also polymers. polymers Synthetic organic compounds with high molecular weights and composed of repeating chemical units (monomers); they may be polyelectrolytes, such as water-soluble flocculents or water-insoluble ion exchange resins, or insoluble uncharged materials, such as those used for plastic or plastic-lined pipe and plastic trickling filter media. polyvinyl chloride (PVC) An artificial polymer made from vinyl chloride monomer (CH2CHCl)n; frequently used in pipes, sheets, and vessels for transport, containment, and treatment in water and wastewater facilities. See also polymers. population dynamics The ever-changing numbers of microscopic organisms within the activated sludge process. population equivalent The estimated population that would contribute a given amount of a specific waste parameter (5-day biochemical oxygen demand, suspended solids, or flow); typically applied to industrial waste. Domestic wastewater contains material that consumes, on average, 0.08 kg/cap_d (0.17 lb of oxygen/d/cap), as measured by the standard biochemical oxygen demand test. For example, if an industry discharges 454 kg (1000 lb) of biochemical oxygen demand per day, its waste is equivalent to the domestic wastewater from 6000 persons (1000/0.17 = approximately 6000). ppm parts per million. precipitate (1) To condense and cause to fall as precipitation, as water vapor condenses and falls as rain. (2) The separation from solution as a precipitate. (3) The substance that is precipitated.
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pressure (1) The total load or force acting on a surface. (2) In hydraulics, unless otherwise stated, the pressure per unit area or intensity of pressure above local atmospheric pressure expressed in kilograms per square centimeter (kg/cm2) or pounds per square inch (psi). pressure gauge A device for registering the pressure of solids, liquids, or gases. It may be graduated to register pressure in any units desired. protozoa Small one-celled animals including amoebae, ciliates, and flagellates. range A measure of the variability of a quantity; the difference between the largest and smallest values in the sequence of values of the quantity; rate (1) The speed at which a chemical reaction occurs. (2) Flow volume per unit time. reaction rate The rate at which a chemical reaction progresses, recorder (1) A device that makes a graph or other record of the stage, pressure, depth,~velocity,
Basic Laboratory Procedures for the Operator-Analyst or the movement or position of water-controlling devices, typically as a function of time. See also indicator. (2) The person who records observational data. reduce The opposite of oxidize. The action of a substance to decrease the positive valence of an ion. reduction The addition of electrons to a chemical entity, decreasing its valence. See also oxidation. relative humidity (1) The amount of water vapor in the air; expressed as a percentage of die maximum amount that the air could hold at the given temperature. (2) The ratio of the actual water vapor pressure to the saturation vapor pressure. residue (1) The equilibrium quantity of a compound or element remaining in an organism after uptake and clearance. (2) The dry solid remaining after evaporation. respiration Intake of oxygen and discharge of carbon dioxide as a result of biological oxidation. rotifer Minute, multicellular aquatic animals with rotating cilia on the head and forked tails. Rotifers help stimulate microfloral activity and decomposition, enhance oxygen penetration, and recycle mineral nutrients. Salmonella A genus of aerobic, rod-shaped, typically motile bacteria that are athogenic for man and other warm-blooded animals. sampler A device used with or without flow measurement to obtain a portion of liquid for analytical purposes. May be designed for taking single samples (grab), composite samples, continuous samples, or periodic samples. Sarcodina Species of amoeba found in wastewater. Does not play a significant role in the activated sludge process other than as an indication of startup or the passing of a toxic influence.
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saturated air Air containing all the water vapor that it is capable of holding at a given temperature and pressure. saturated liquid Liquid that contains at a given temperature as much of a solute as it can retain in the presence of an excess of that solute. Secchi disk Tool to measure the clarity of water. second-stage BOD That part of oxygen demand associated with the biochemical oxidation of nitrogenous material. As the term implies, oxidation of nitrogenous materials typically does not start until a portion of the carbonaceous material has been oxidized during the first stage. settleability The tendency of suspended solids to settle. settleability test A determination of the settleability of solids in a suspension by measuring the volume of solids settled out of a measured volume of sample in a specified interval of time, typically reported in milliliters per liter (mL/L). Also called the Imhoffcone test. settleable solids (1) That matter in wastewater that will not stay in suspension during a preselected settling period, such as 1 hour, but settles to the bottom. (2) In the Imhoff cone test, the volume of matter that settles to the bottom of the cone in 1 hour. (3) Suspended solids that can be removed by conventional sedimentation. settleometer test Provides an indication of the solids-liquid separation capability of sludge. Mixed liquor suspended solids are placed in a 2-L or larger beaker and the solids level is measured over a period of 30 minutes to determine the rate of settling. slope (1) The inclination of gradient from the horizontal of a line or surface. The degree of inclination is typically expressed as a ratio such as 1:25, indicating unit rise in 25 units of horizontal distance, or in a decimal fraction (0.04), degrees (2 deg, 18 minutes), or percent (4%). (2) Inclination of the invert of a conduit expressed as a decimal or as meters (feet) per stated length measured horizontally in meters. (3) In plumbing, the inclination of a conduit, typically expressed in meter length of pipe. sludge concentration Any process of reducing the water content of sludge leaving the sludge in a fluid condition. sludge density index (SDI) A measure of the degree of compaction of a sludge after settling in a graduated container, expressed as milliliters per gram (mL/g). The sludge volume index is the reciprocal of the sludge density index. sludge volume index (SVI) The ratio of the volume (in milliliters) of sludge settled from a 1000-mL sample in 30 minutes to the concentration of mixed liquor (in mg/L) multiplied by 1000. soda ash A common name for commercial sodium carbonate (Na2COi).
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sodium bisulfate (NaHS03) A salt used for reducing chlorine residuals; a strong reducing agent; typically found in white powder or granular form in strengths up to 44%. At a strength of 38%, 1.46 parts will consume 1 part of chlorine residual. sodium carbonate (Na2C03) A salt used in water treatment to increase the alkalinity or pH of water or to neutralize acidity. Also called soda ash. sodium Jiydroxide (NaOH) A strong caustic chemical used in treatment processes to neutralize acidity, increase alkalinity, or raise the pH value. Also known as caustic soda, sodium hydrate, lye, and white caustic. sodium hypochlorite (NaOCl) A water solution of sodium hydroxide and chlorine iri which sodium hypochlorite is the essential ingredient. sodium mctabisulfite (Na2S2Or>) A cream-colored powder used to conserve chlorine residual; 1.34 parts of Na2S205 will consume 1 part of chlorine residual. sparger An air diffuser designed to give large bubbles, used singly or in combination with mechanical aeration devices. Basic Laboratory Procedures for the Operator-Analyst species A subdivision of a genus having members differing from other members of the same genus in minor details. specific gravity The ratio of the mass of a body to the mass of an equal volume of water at a specific temperature, typically 20 째C (68 째F). specific oxygen uptake rate Measures the microbial activity in a biological system expressed in milligrams of 02/g-h of volatile suspended solids. Also called respiration rate. stalked ciliates Small, one-celled organisms possessing cilia (hair-like projections used for feeding) that are not motile. They develop at lower prey densities, long solids retention times, and low foodto-microorganism ratios. Standard Methods (1) An assembly of analytical techniques and descriptions commonly accepted in water and wastewater treatment (Standard Methods for the Examination of Water and Wastewater) published jointly by the American Public Health Association, the American Water Works Association, and the Water Environment Federation. (2) Validated methods published by professional organizations and agencies covering specific fields or procedures. These include, among others, the American Public Health Association, American Public Works Association, American Society of Civil Engineers, American Society of Mechanical Engineers, American Society for Testing and Materials, American Water Works Association, U.S. Bureau of Standards, U.S. Standards Institute (formerly American Standards Association), U.S. Public Health Service, Water Environment Federation, and U.S. Environmental Protection Agency.
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stoichiometric Pertaining to or involving substances that are in the exact proportions required for a given reaction. substrate (1) Substances used by organisms in liquid suspension. (2) The liquor in which activated sludge or other matter is kept in suspension. suctorians Ciliates that are stalked in the adult stage and have rigid tentacles to catch prey. sulfate-reduchig bacteria Bacteria that obtain their energy by oxidizing organic compounds or molecular hydrogen while reducing sulfate. sulfur bacteria Bacteria capable of using dissolved sulfur compounds in their growth; bacteria deriving energy from sulfur or sulfur compounds. sulfur cycle A graphical presentation of the conservation of matter in nature showing the chemical transformation of sulfur through various stages of decomposition and assimilation. The various chemical forms of sulfur as it moves among living and nonliving matter is used to illustrate general biological principles that are applicable to wastewater and sludge treatment. supersaturation An unstable condition of a vapor in which its density is greater than that typically in equilibrium under the given conditions. surfactant A surface-active agent, such as branched alkylbenzene sulfonates or linear alkylbenzene sulfonates, that concentrates at interfaces, forms micelles, increases solution, lowers surface tension, increases adsorption, and may decrease flocculation. temperature (1) The thermal state of a substance with respect to its ability to transmit heat to its environment. (2) The measure of the thermal state on some arbitrarily chosen numerical scale. See also Celsius, centigrade, and Fahrenheit. temporary hardness Hardness that can be removed by boiling; more properly called carbonate hardness. See also carbonate hardness and hardness. thermophilic range That temperature range most conducive to maintenance of optimum digestion by thermophilic bacteria, generally accepted as between 49 and 57 째C (120 and 135 째F). See also thermophilic digestion. threshold odor The minimum odor of the water sample that can barely be detected after successive dilutions with odorless water. Also called odor threshold. threshold odor number The greatest dilution of a sample with odor-free water that yields a definitely perceptible odor. titration The determination of a constituent in a known volume of solution by the measured addition of a solution of known strength to completion of tine reaction as signaled by observation of an endpoint.
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total carbon A quantitative measure of both total inorganic and total organic carbon as determined instrumentally by chemical oxidation to carbon dioxide and subsequent infrared detection in a carbon analyzer. See also total organic carbon. total dissolved solids (TDS) The sum of all dissolved solids (volatile and nonvolatile). total Kjeldahl nitrogen (TKN) The combined amount of organic and ammonia nitrogen. total organic carbon (TOC) The amount of carbon bound in organic compounds in a sample. Because all organic compounds have carbon as the common element, total organic carbon measurements provide a fundamental means of assessing the degree of organic pollution. total oxygen demand (TOD) A quantitative measure of all oxidizable material in a sample water or wastewater as determined instrumentally by measuring the depletion of oxygen after hightemperature combustion. See also chemical oxygen demand and total organic carbon. total solids The sum of dissolved and suspended solid constituents in water or wastewater. total suspended solids (TSS) The amount of insoluble solids floating and in suspension in the wastewater. Also referred to as total nonfilterable residue". Basic Laboratory Procedures for the Operator-Analyst toxicant A substance that kills or injures an organism through chemical, physical, or biological action; examples include cyanides, pesticides, and heavy metals. toxicity The adverse effect that a biologically active substance has, at some concentration, on a living entity. trace nutrients Substances vital to bacterial growth. Trace nutrients are defined in this text as nitrogen, phosphorus, and iron. tri-halomethanes (THM) Derivatives of methane (CH4) in which three halogen atoms (chlorine, bromine, or iodine) are substituted for three of the hydrogen atoms. tubing Flexible pipe of small diameter, typically less than 5.1 cm (2 in.). turbidimeter An instrument for measurement of turbidity in which a standard suspension is used for reference. turbidity (1) A condition in water or wastewater caused by die presence of suspended matter and resulting in the scattering and absorption of light. (2) Any suspended solids imparting a visible haze or cloudiness to water that can be removed by filtration. (3) An analytical quantity typically reported in turbidity units determined by measurements of light scattering. See also formazine turbidity unit and nephelometric turbidity unit. ultimate biochemical oxygen demand (BODu) (1) Commonly, the total quantity of oxygen required to completely satisfy the first-stage biochemical oxygen demand. (2) More strictly, the quantity of oxygen required to completely satisfy both first-stage and second-stage biochemical oxygen demand.
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ultraviolet radiation (UV) Light waves shorter than the visible blue-violet waves of the spectrum. valence An integer representing the number of hydrogen atoms with which one atom of an element (or one radical) can combine (negative valence), or the number of hydrogen atoms the atom or radical can displace (positive valence). vapor (1) The gaseous form of any substance. (2) A visible condensation such as fog, mist, or steam that is suspended in air. virus The smallest (10 to 300 mm in diameter) life form capable of producing infection and diseases in man and animals. viscosity The molecular attractions within a fluid d .at make it resist a tendency to deform under applied forces. volatile Capable of being evaporated at relatively low temperatures. volatile acids Fatty acids containing six or fewer carbon atoms. They are soluble in water and can be steam-distilled at atmospheric pressure. They have pungent odors and are often produced during anaerobic decomposition. volatile solids' Materials, generally organic, that can be driven off from a sample by heating, typically to 550 째C (1022 째F); nonvolatile inorganic solids (ash) remain. volatile suspended solids (VSS) That fraction of suspended solids, including organic matter and volatile inorganic salts, that will ignite and burn when placed in an electric muffle furnace at 550 째C (1022 째F) for 60 minutes. volumetric Pertaining to measurement by volume. watt The electrical unit of power. Power is the measure of the rale of doing work.
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ASSIGNMENTS SECTION
QUESTIONS 1. Sample containers must always be cleaned before being filled. True or False?
2. What is the most frequently used means of sample preservation ?
3. Which is the preservant that is added to samples to prevent the loss of volatile compounds through the formation of a salt?
4. Microbiological samples need to be collected in sterile containers. True or False?
5. Which are the two basic types of samples taken in a WWTP?
6. If the flow to be sampled occurs intermittently for short durations, which type of sample is recommended?
NIREAS VOLUME 6 139 7. Which process generally requires more sampling and testing to maintain adequate process control than any of the other unit processes in the wastewater treatment system?
8. What is the best pH range in a sample taken from the aeration tank effluent ?
9. In an activated sludge process when the temperature increases organism activity increases. True or False?
10. In an activated sludge process when the temperature increases oxygen solubility increases. True or False?
11. What is the normal range of DO in an aeration tank ?
12. By which test you can determine if the activated sludge is old (too many solids) or bulking (not settling)?
NIREAS VOLUME 6 140 13. An increase in TKN indicates that nitrification is decreasing; a decrease in TKN indicates that nitrification is increasing. True or False?
14. Five measurements of TSS are given bellow : 15, 23, 14, 19 and 24 mg/L. Whatâ&#x20AC;&#x2122;s the mean value? Are results within standard deviations?
15. As a general rule, differences among calibration standard concentrations should not be greater than 1 order of magnitude. True or False?
16. If concentration is 1000 mg/L, what is the equivalent result in percent by weight (w.w. %) value, when the specific gravity is 0,95 kg/L?
17. if the operator is using a 100-ppm standard and would like to make 100 mL of 10-ppm standard dilution, what is the volume of the standard that shall be used? What is the volume of the distilled water that shall be used?
18. In which principal method Titrimetric analyses are based?
NIREAS VOLUME 6 141 19. Can Chlorine affect BOD measurement?
20. How can you estimate the amount of BOD when measuring oxygen levels in a site?
21. Solids are separated into two classes: suspended solids and dissolved solids. True or False?
22. Report the most important protective gear that is required in a WWTP laboratory.
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SUGGESTED ANSWARS: 1. True 2. Refrigeration at temperatures near freezing (6 째C) 3. Alkali, typically sodium hydroxide (NaOH), 4. True 5. Grab samples and composite samples 6. Grab sample 7. The activated sludge process 8. 6.5 to 8.5 9. True 10. False 11. 1 to 3 mg/L 12. By Running the settleability test 13. True 14. 19 mg/L. Yes, all results are within standard deviations 15. True 16. 0,095% 17. the volume of the standard that shall be used is 10 ml the volume of the distilled water that shall be used is 90 ml 18. Titrimetric analyses are based on adding a solution of known strength (the titrant, which must have an exact known concentration) to a specific volume of a treated sample in the presence of an indicator. The indicator produces a color change indicating that the reaction is complete 19. Yes 20. Biochemical oxygen demand measurement requires taking two samples at each site. One is tested immediately for dissolved oxygen; the second is incubated in the dark at 20째C for 5 days and then tested for dissolved oxygen remaining. The difference in oxygen levels (in mg/L) between the first test and the second test is the amount of BOD. 21. True 22. Safety goggles, Disposable latex gloves, laboratory coat and rubber apron, sed-toe shoes (preferably chemical-resistant)
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