Volume 1 final b

ELEARNI NG FOR THE OPERATORS OFWASTEWATER TREATMENT

VOLUME 1

PRELI MI NARY APPROACH

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1.1 Role and Contribution of the Operators in the Wastewater Management Operators' role for the society, for the environment, for the sustainable development, in a holistic Environmental management with proper optimized Wastewater Management.

1.1.1 Introduction Before modern society entered the scene, water was purified in a natural cycle as shown below:

Fig 1.1.1. Simplified natural purification cycle of water But modern society and the intensive use of the water resources and the resulting water pollution could not wait for sun, wind, and time to accomplish the purification of soiled water; consequently, treatment plants were built. Thus, nature was given an assist by a team consisting of designers, builders, and treatment plant operators.

Designers and builders occupy the scene only for an interval, but operators go on forever. They are the final and essential link in maintaining and protecting the aquatic environment upon which all life depends.

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Fig 1.1.2. Nowadays complicated natural artificial purification cycle of water The Treatment Plant Operators have very important role in the society, for the environment, for the sustainable development, in a holistic Environmental management

1.1.2 What Does a Treatment Plant Operator Do? Simply described, the operator keeps a wastewater (sewage) treatment plant working. Physically, the operator turns valves, pushes switches, collects samples, lubricates equipment, reads gauges, and records data. An operator may also maintain equipment and plant areas by painting, weeding, gardening, repairing machinery, and replacing parts.

Mentally, an operator inspects records, observes conditions, makes calculations to determine that the plant is working effectively, and predicts necessary maintenance and facility needs to ensure continued effective operation of the plant. The operator also has an obligation to explain to supervisors, councils, civic bodies, and the general public what the plant does and, most importantly, why its continued and expanded financial support is vital to the welfare of the community.

1.1.3 Who Does the Treatment Plant Operator Work For? An operator's paycheck usually comes from a city, sanitation district, or other public agency. The operator may, however, be employed by one of the many industries, large hotels, campings and other facilities, that operate their own treatment plants.

Operators also may work for private contractors that are retained to operate and maintain municipal or industrial wastewater treatment plants. As an operator, you are responsible to your employer for maintaining an economical and efficient operating facility. An even greater obligation rests with the operator because the great numbers of people who rely on downstream water supplies are totally

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dependent on the operator's competence and trustworthiness for their welfare. In the final analysis, the operator is really working for these vitally affected downstream water users.

1.1.4 What Does It Take to Be a Treatment Plant Operator?

Desire. First you must choose to enter this profession. You can do it with a grammar school, a high school, a college or a technical university or related scientific education. The amount of education needed depends largely on the type of treatment facility and also local certification and entry-level job requirements. While some jobs will always exist for manual labor, the real and expanding need is for trained operators. New techniques, advanced equipment, and increasing instrumentation require a new breed of operator, one who is willing to learn today, and gain tomorrow, for surely your plant will move toward newer and more effective operating procedures and treatment processes. Indeed, the truly service-minded operator assists in adding to and improving the plant performance on a continuing basis.

You can be an operator tomorrow by beginning your learning today; or you can be a better operator, ready for advancement, by accelerating your learning today.

This training course, then, is your start toward a better tomorrow, both for you and for the public who will receive better water from your efforts.

1.1.5 Your Personal Training Course Beginning on this page, you are embarking on a training course that has been carefully prepared to allow you to improve your knowledge of and ability to operate a wastewater treatment plant. You will be able to proceed at your own pace; you will have an opportunity to learn a little or a lot about each topic. The course has been prepared this way to fit the various needs of operators, depending on what kind of plant you have or how much you need to learn about it. To study for certification examinations, you will have to cover all the material. You will never know everything about your plant or about the wastewater that flows through it, but you can begin to answer some very important questions about how and when certain things happen in the plant. You can also learn to manipulate your plant so that it operates at maximum efficiency.

1.1.6 What Do You Already Know?

If you already have some experience operating a wastewater treatment plant, you may use the first three chapters for a review. If you are relatively new to the wastewater treatment field, these chapters will provide you with the background information necessary to understand the later chapters. The remainder of this introductory chapter describes your role as a protector of water quality, your qualifications to do your job, a little about staffing needs in the wastewater

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treatment field, and some information on other training opportunities. We focus in odors’ problem in the Chapter 3,considering this main issue for people in warm climates and in any case of neighboring areas with a wastewater treatment plant.

1.1.7 The Water Quality Protection processes: Historically, we have shown a great lack of interest in the protection of our water resources. We have been content to think that "the solution to pollution is dilution."

For years we were able to dump our wastes with little or no treatment back into the nearest RECEIVING WATERS, or to the nearest stream or to the creek or to the sea or to a well, with the easiest way.

As long as there was enough dilution water to absorb the waste material, nature took care of our disposal problems for us. As more and more towns and industry sprang up, waste loads increased until the natural purification processes could no longer do the job. Many waterways were converted into open sewers.

Unfortunately, for many areas this did not signal the beginning of a cleanup campaign. It merely increased the frequency of the cry: "We do not have the money for a treatment plant," or the ever-popular, "If we make industries treat their wastes they will move to another city or to another area, away from us." Thus, the pollution of our waters (surface, underground and sea in gulf areas) increased.

Within the last 30 years, we have seen many changes in this depressing picture. We now realize that we must give nature a hand by treating wastes before they are discharged. Adequate treatment of wastes will not only protect our health and that of our downstream neighbors; it can also increase property values, allow game fishing and various recreational uses to be enjoyed, and attract water-using industries to the area. Today we are seeing massive efforts being undertaken to control water pollution and improve water quality throughout the nation. This includes the efforts not only of your own community, area, and country, but also of the European Union.

Great sums of public and private funds are now being invested in large, complex municipal and industrial wastewater treatment facilities to overcome this pollution; and you, the treatment plant operator, will play a key role in the battle. Without efficient operation of your plant, much of the research, planning, and building that has been done and will be done to accomplish the goals of water quality control in your area will be wasted. You are the difference between a facility and a performing unit. You are, in fact, a water quality protector on the front line of the water pollution battle.

The receiving water quality standards and waste discharge requirements that your plant has been built to meet have been formulated to protect the water users downstream from your plant. These uses may include domestic water supply,

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industrial water supply, agricultural water supply, stock and wildlife watering, propagation of fish and other aquatic and marine life, shellfish culture, swimming and other water contact sports, boating, aesthetic enjoyment, hydroelectric power, navigation, and others.

Therefore, you have an obligation to the users of the water downstream, as well as to the people of your district or municipality. You are the key water quality protector and must realize that you are in a responsible position. The main benefit of a successful wastewater treatment program is the protection of public health.

1.1.8 YOUR QUALIFICATIONS The skill and ability required for your job depend to a large degree on the size and type of treatment plant where you are employed. You may work at a large modern treatment plant serving several hundred thousand persons and employing a hundred or more operators. In this case, you are probably a specialist in one or more phases of the treatment process.

On the other hand, you may operate a small plant serving only a thousand people or fewer. You may be the only operator at the plant or, at best, have only one or two additional employees. If this is the case, you must be a "jack-of-all-trades" because of the diversity of your tasks.

1.1.8.1 Your Job To describe the operator's duties, let us start at the beginning. Let us say that the need for a new or improved wastewater treatment plant has long been recognized by the community. The community has voted to issue the necessary bonds to finance the project, and the consulting engineers have submitted plans and specifications. It is in the best interests of the community and the consulting engineer that you be in on the ground floor planning. If it is a new plant, you should be present or at least available during the construction period in order to become completely familiar with the entire plant, including the equipment and machinery and their operation. This will provide you with the opportunity to relate your plant drawings to actual facilities.

You and the engineer should discuss how the treatment plant should best be run and the means of operation the designer had in mind when the plant was designed. If it is an old plant being remodeled or expanded, you are in a position to offer excellent advice to the consulting engineer. Your experience provides valuable technical knowledge concerning the characteristics of wastewater, its sources, and the

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limitations of the present facilities. Together with the consultant, you are a member of an expert team able to advise the district or city.

Once the plant is operating, you become an administrator. In a small plant, your duties may not include supervision of personnel, but you are still in charge of records. You are responsible for operating the plant as efficiently as possible, keeping in mind that the primary objective is to protect the receiving water quality by continuous and efficient plant performance. Without adequate, reliable records of every phase of operation, the effectiveness of your operation has not been documented (recorded).

You may also be the budget administrator. Most certainly you are in the best position to give advice on budget requirements, management problems, and future planning. You should be aware of the necessity for additional expenditures, including funds for plant enlargement, equipment replacement, and laboratory requirements.

You should recognize and define such needs in sufficient time to inform the proper officials to enable them to accomplish early planning and budgeting.

You are in the field of public relations and must be able to explain the purpose and operation of your plant to visitors, civic organizations, school classes, representatives of news media, and even to city council or directors of your district. Public interest in water quality is increasing, and you should be prepared to conduct plant tours that will contribute to public acceptance and support. A well-guided tour for officials of regulatory agencies or other operators may provide these people with sufficient understanding of your plant to allow them to suggest helpful solutions to operational problems. The appearance of your plant indicates to the visitor the type of operation you maintain. If the plant is dirty and rundown with flies and other insects swarming about, you will be unable to convince your visitors that the plant is doing a good job. Your records showing a high-quality effluent will mean almost nothing to these visiting citizens unless your plant appears clean and well maintained and the effluent looks good.

Another aspect of your public relations duties is your dealings with the downstream water user. Unfortunately, the operator is often considered by the downstream user as a polluter rather than a water quality protector. Through a good public information program, backed by facts supported by reliable data, you can correct the impression held by the downstream user and establish "good neighbor" relations.

This is indeed a challenge. Again, you must understand that you hold a very responsible position and be aware that the sole purpose of the operation of your plant is to protect the downstream user, be that user a private property owner, another city or district, an industry, or a fisherman.

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You are required to understand certain laboratory procedures in order to conduct various tests on samples of wastewater and receiving waters. On the basis of the data obtained from these tests, you may have to adjust the operation of the treatment plant to meet receiving stream standards or discharge requirements.

As an operator, you must have a knowledge of the complicated mechanical principles involved in many treatment mechanisms. In order to measure and control the wastewater flowing through the plant, you must have some understanding of hydraulics. Practical knowledge of electric motors, circuitry, and controls is also essential.

Safety is a very important operator responsibility. Unfortunately, too many operators take safety for granted. This is one reason why the wastewater treatment industry has one of the worst safety records of any industry. You have the responsibility to be sure that your treatment plant is a safe place to work and visit.

Everyone must follow safe procedures and understand why safe procedures must be followed at all times. All operators must be aware of the safety hazards in and around treatment plants. You should plan or be a part of an active safety program.

Chief operators frequently have the responsibility of training new operators and must encourage all operators to work safely.

Clearly then, today's wastewater treatment plant operator must possess a broad range of qualifications.

1.1.9 STAFFING NEEDS AND FUTURE JOB OPPORTUNITIES The wastewater treatment field, like so many others, is changing rapidly. New plants are being constructed and old plants are being modified and enlarged to handle the wastewater from our growing population and to treat the new chemicals being produced by our space-age technology. Operators, maintenance personnel, foremen, managers, instrumentation experts, and laboratory technicians are sorely needed.

A look at past records and future predictions indicates that wastewater treatment is a rapidly growing field. According to our estimations , water and wastewater treatment plant and system operators held about 1,500 jobs in 2010 (in Greece Almost 4 in 5 operators worked for local governments. Others worked primarily for private water, wastewater, and other systems utilities and for private waste treatment and disposal and waste management services companies. Private firms are increasingly providing operation and management services to local governments on a contract basis. Water and wastewater treatment plant and system operators were employed throughout the country, but most jobs were in larger towns and

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cities. Although nearly all operators worked full time, those in small towns may work only part time at the treatment plant, with the remainder of their time spent handling other municipal duties. Employment of water and wastewater treatment plant and system operators is expected to grow about as fast as the average for all occupations through the year 2014. Current information reveals that many current operators will be retiring in the near future and may create an even greater demand for operators. Factors contributing to the increase include population growth, retirement of many current operators, regulatory requirements, more sophisticated treatment, and operator certification regulations. The need for trained operators is increasing rapidly and is expected to continue to grow in the future.

1.1.10 TRAINING YOURSELF TO MEET THE NEEDS This training course is not the only one available to help you improve your abilities.

Several 0rganizations (authorities or Institutes or training centers or universities have offered various types of both long- and short-term operator training through their health departments and water pollution control associations have provided training classes conducted by members of the associations, largely on a volunteer basis. This training system is focusing to help local or national organizations in each country to improve or develop an e-learning system modified according their real educational needs for wwtp operators.

Listed below are three very good references in the field of wastewater treatment plant operation that are frequently referred to throughout this course.

"MOP 11." OPERATION OF MUNICIPAL WASTEWATER TREATMENT PLANTS (MOP 11). Obtain from Water Environment Federation (WEF), Publications Order Department, 601 Wythe Street, Alexandria, VA 22314-1994.

These publications cover the entire field of treatment plant operation. At the end of many of the chapters yet to come, lists of other the increase include population growth, retirement of many current operators, regulatory requirements, more sophisticated treatment, and operator certification regulations. The need for trained operators is increasing rapidly and is expected to continue to grow in the future.

1.1.11 TRAINING YOURSELF TO MEET THE NEEDS This training course is not the only one available to help you improve your abilities.

More‌ In USA many states have offered various types of both long- and short-term operator training through their health departments and water pollution control associations

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have provided training classes conducted by members of the associations, largely on a volunteer basis. The Water Environment Federation (WEF) has developed two visual aid training courses to complement its Manual of Practice No. 11. State and local colleges have provided valuable training under their own sponsorship or in partnership with others. Many state, local, and private agencies have conducted both long- and short-term training as well as interesting and informative seminars.

The California Water Environment Association has prepared several excellent study guides for operators. Excellent textbooks have been written by many state agencies.

Those of the New York State Health Department and the Texas Water Utilities Association deserve special attention. The Canadian government has developed very good training manuals for operators.

Listed below are three very good references in the field of wastewater treatment plant operation that are frequently referred to throughout this course. The name in quotes represents the term usually used by operators when they mention the reference. Prices listed are those available when this manual was published and will probably increase in the future.

"MOP 11." OPERATION OF MUNICIPAL WASTEWATER TREATMENT PLANTS (MOP 11). Obtain from Water Environment Federation (WEF), Publications Order Department, 601 Wythe Street, Alexandria, VA 22314-1994. Order No. M05110. Price to members, $120.00; nonmem-bers, $148.00; plus shipping and handling.

"NEW YORK MANUAL." MANUAL OF INSTRUCTION FOR WASTEWATER TREATMENT PLANT OPERATORS (two-volume set) distributed in New York by the New York State Department of Health, Office of Public Health Education, Water Pollution Control Board. Distributed outside of New York State by Health Education Services, PO Box 7126, Albany, NY 12224. Price $20.00 for the two-volume set, plus $5.00 shipping and handling. Make checks payable to Health Education Services.

'TEXAS MANUAL" MANUAL OF WASTEWATER TREATMENT, published by the Texas Water Utilities Association.

These publications cover the entire field of treatment plant operation. At the end of many of the chapters yet to come, lists of other references will be provided.

Careers, Options, Chances, Role of all partners (Administration, Authorities), philosophy of collaboration What Pay Can a Treatment Plant Operator Expect?

In Euros? Prestige? Job satisfaction? Community service? In opportunities for advancement? By whatever scale you use, returns are what you make them. If you

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choose a large municipality, the pay is good and advancement prospects are tops.

Choose a small town and pay may not be as good, but job satisfaction, freedom from time-clock hours, community service, and prestige may well add up to outstanding personal achievement. The total reward depends on you.

In the work of an operator, the problems are different, mainly dependent from the area in the country, the legislation, the size of the plant, the type of treatment and many other

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Main Terms Used in wastewater management: AEROBIC BACTERIA Bacteria that will live and reproduce only in an environment containing oxygen that is available for their respiration (breathing), namely atmospheric oxygen or oxygen dissolved in water. Oxygen combined chemically, such as in water molecules (H 20), cannot be used for respiration by aerobic bacteria.

ALGAE Microscopic plants containing chlorophyll that live floating or suspended in water.

They also may be attached to structures, rocks, or other submerged surfaces. Excess algal growths can impart tastes and odors to potable water. Algae produce oxygen during sunlight hours and use oxygen during the night hours. Their biological activities appreciably affect the pH, alkalinity, and dissolved oxygen of the water.

ANAEROBIC BACTERIA Bacteria that live and reproduce in an environment containing no free or dissolved oxygen. Anaerobic bacteria obtain their oxygen supply by breaking down chemical compounds that contain oxygen, such as sulfate (S0 42~).

BOD Biochemical Oxygen Demand. The rate at which organisms use the oxygen in water or wastewater while stabilizing decomposable organic matter under aerobic conditions. In decomposition, organic matter serves as food for the bacteria and energy results from its oxidation. BOD measurements are used as a surrogate measure of the organic strength of wastes in water.

BIOCHEMICAL OXYGEN DEMAND (BOD) See BOD. BIOCHEMICAL OXYGEN DEMAND (BOD) TEST A procedure that measures the rate of oxygen use under controlled conditions of time and temperature. Standard test conditions include dark incubation at 20°C for a specified time (usually five days).

COLIFORM A group of bacteria found in the intestines of warm-blooded animals (including humans) and also in plants, soil, air, and water. The presence of coliform bacteria is an indication that the water is polluted and may contain pathogenic (diseasecausing) organisms. Fecal coliforms are those coliforms found in the feces of various warm-blooded animals, whereas the term "coliform" also includes other environmental sources.

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DISINFECTION The process designed to kill or inactivate most microorganisms in water or wastewater, including essentially all pathogenic (disease-causing) bacteria. There are several ways to disinfect, with chlorination being the most frequently used in water and wastewater treatment plants. Compare with STERILIZATION. EFFLUENT Water or other liquid—raw (untreated), partially treated, or completely treated— flowing FROM a reservoir, basin, treatment process, or treatment plant.

EVAPOTRANSPIRATION The process by which water vapor is released to the atmosphere from living plants.

Also called TRANSPIRATION. The total water removed from an area by transpiration (plants) and by evaporation from soil, snow, and water surfaces.

INORGANIC WASTE Waste material such as sand, salt, iron, calcium, and other mineral materials that are only slightly affected by the action of organisms. Inorganic wastes are chemical substances of mineral origin; whereas organic wastes are chemical substances usually of animal or plant origin. Also see NONVOLATILE MATTER, ORGANIC WASTE, and VOLATILE SOLIDS. MILLIGRAMS PER LITER, mg/L A measure of the concentration by weight of a substance per unit volume in water or wastewater. In reporting the results of water and wastewater analysis, mg/L is preferred to the unit parts per million (ppm), to which it is approximately equivalent.

NUTRIENT NUTRIENT Any substance that is assimilated (taken in) by organisms and promotes growth.

Nitrogen and phosphorus are nutrients that promote the growth of algae. There are other essential and trace elements that are also considered nutrients. Also see NUTRIENT CYCLE NUTRIENT CYCLE The transformation or change of a nutrient from one form to another until the nutrient has returned to the original form, thus completing the cycle. The cycle may take place under either aerobic or anaerobic conditions.

ORGANIC WASTE Waste material that may come from animal or plant sources. Natural organic wastes generally can be consumed by bacteria and other small organisms. Manufactured or synthetic organic wastes from metal finishing, chemical manufacturing, and petroleum industries may not normally be consumed by bacteria and other organisms. Also see INORGANIC WASTE and VOLATILE SOLIDS PATHOGENIC ORGANISMS

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Bacteria, viruses, cysts, or protozoa that can cause disease (giardiasis, cryptosporidiosis, typhoid, cholera, dysentery) in a host (such as a person). There are many types of organisms that do not cause disease and are not called pathogenic.

Many beneficial bacteria are found in wastewater treatment processes actively cleaning up organic wastes pH pH is an expression of the intensity of the basic or acidic condition of a liquid.

Mathematically, pH is the logarithm (base 10) of the reciprocal of the hydrogen ion activity. The pH may range from 0 to 14, where 0 is most acidic, 14 most basic, and 7 neutral.

POLLUTION The impairment (reduction) of water quality by agricultural, domestic, or industrial wastes (including thermal and radioactive wastes) to a degree that the natural water quality is changed to hinder any beneficial use of the water or render it offensive to the senses of sight, taste, or smell or when sufficient amounts of wastes create or pose a potential threat to human health or the environment.

PRIMARY TREATMENT A wastewater treatment process that takes place in a rectangular or circular tank and allows those substances in wastewater that readily settle or float to be separated from the wastewater being treated. A septic tank is also considered primary treatment.

RECEIVING WATER A stream, river, lake, ocean, or other surface or groundwaters into which treated or untreated wastewater is discharged.

SECONDARY TREATMENT A wastewater treatment process used to convert dissolved or suspended materials into a form more readily separated from the water being treated. Usually, the process follows primary treatment by sedimentation. The process commonly is a type of biological treatment followed by secondary clarifiers that allow the solids to settle out from the water being treated A condition produced by anaerobic bacteria. If severe, the sludge produces hydrogen sulfide, turns black, gives off foul odors, con¬tains little or no dissolved oxygen, and the wastewater has a high oxygen demand.

STABILIZATION STABILIZATION Conversion to a form that resists change. Organic material is stabilized by bacteria that convert the material to gases and other rela¬tively inert substances. Stabilized organic material generally will not give off obnoxious odors.

The removal or destruction of all microorganisms, including pathogens and other bacteria, vegetative forms, and spores. Compare with DISINFECTION.The process by which water vapor is released to the atmosphere by living plants. This process is similar to people sweating. Also see EVAPOTRANSPIRATION.

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1.2 Basic Information And Knowledge (Environment protection, Pollution- Impacts of Pollution, Contamination, Eutrophication) 1.2.1. Definitions Pollution is the action of environmental contamination with man-made waste.

(Marriam-Webster) This includes mainly land, water, and air. Pollution can come in various forms including the lesser-known noise, light, and thermal pollution. Of all the First World countries, the United States and China and then Europe are the most polluting areas on Earth, according to various statistical indications.

Fig.1.2.1 Land Pollution

Fig.1.2.2 Water Pollution

Fig.1.2.3. Air Pollution

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Fig 2.4 How air pollutants pollute the water bodies From pictures is clear that pollution is everywhere. Pollution is a global crisis. It is not an isolated occurrence, but affects every person on Earth. We must become more conscientious and aware that we are not just Americans but global citizens that must take care of the world in which we live!

1.2.1.2 Contamination: The prevention and control of emission is the best way to solve the problems of pollution and eliminate the impacts. the therapy from the impacts of pollution has usually high cost to the society, to the humans'health and to the environment.

More‌ SOME KNOWN IMPACTS OF POLLUTION TO HEALTH ARE REFFERED BELOW: http://www.pages.drexel.edu/~cy34/health.htm

1.2.2 Some Basics Related With The Cycle Of Water And The Pollution: 1.2.2.1 What is a watershed?

A watershed is an area of land that drains to a specific stream, river, or lake.

The limits of a watershed vary with scale: smaller watersheds are nested within larger watersheds. For example the Delaware River Basin includes parts of New York, Pennsylvania, New Jersey, and Delaware, but within this large watershed are many

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smaller watersheds draining to more local streams, rivers, and creeks. And those streams in turn flow into larger rivers that may flow to the Delaware River.

1.2.2.2. The water cycle Water that is delivered to the watershed as precipitation can follow different paths as it makes its way to a local stream. Some precipitation water will infiltrate into the soil, where it might make its way to shallow groundwater and then move laterally slowly in the soil to maintain the base flow of a local stream. Infiltrated water can make its way to deeper groundwater, where it might later be pumped for drinking water or irrigation.

Infiltration is the process of water moving into the soil. During infiltration, the soil is essentially absorbing the rain, irrigation water, or snowmelt.

If precipitation or irrigation falls too quickly to infiltrate into the soil or falls upon impervious services like roofs or driveways, water can move overland as surface runoff. Surface runoff moves quickly to local rivers across the land and through storm drains, exacerbating downstream flooding. Surface runoff is also a concern because it can pick up potential pollutants and deliver them to streams and lakes.

Depending on the weather and land use in the watershed, a significant portion of rain or irrigation applied to the land in a watershed may be returned to the atmosphere through transpiration by plants and evaporation from soil and other surfaces.

Fig. 1.2.4.

A simplified water cycle.

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1.2.2.3 Pollutants in surface water Many natural and human activities have the potential for polluting rivers, lakes, and groundwaters. Point sources of pollution are those where there is an identifiable single point of pollution, such as a factory with a smoke stack or a wastewater treatment plant with a discharge pipe. In contrast, non-point sources of pollution are those which are more dispersed over the landscape, including agriculture, rural or suburban residential development, wildlife, domestic animals, and soil erosion.

A variety of pollutants can be contributed by residential areas, including nutrients (fertilizers), pesticides, sediment from eroded soils, and bacteria. Pollutants include nitrogen and phosphorus from lawn fertilizers, bacteria from pet wastes or the wastes of wild animals, malfunctioning septic systems, metals from deposition on roofs, pesticides applied to homes and lawns, and motor oil and other fluids from leaking automobiles. Each of these has the potential for negative impacts on surface water or groundwater for a variety of desirable water uses including drinking, recreation, and wildlife habitat. While these pollutants can travel with surface runoff, certain pollutants can also move readily with infiltrating water to groundwater. Notably, pollutants that can infiltrate into groundwater include nitrogen in the form of nitrate and certain herbicides.

Fig.1.2.5. Eutrophication in a waterbody after pollution with nutrients

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Fig. 1.2.6. Dead fish in polluted waterbody Excessive algae or vegetation in a lake may be indicators that the lake has been impacted by pollution with nutrients, usually phosphorus. Such impacts can deplete oxygen in the water, killing fish, and make water bodies less enjoyable for swimming and boating.

1.2.2.4 Pollution movement in figures:

Fig. 1.2.6. Simplified contamination transfer to a well aquifer

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Fig. 1.2.7. Thousands of activities make complicated and very difficult to handle the pollution problems in the area surrounding a large urban area

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Your contribution like homeowner to prevent pollution ………………

How to prevent pollution in your house: good management practices The potential for pollution from your property can be minimized by employing good management practices, including the following: • Use soil tests to avoid excess fertilization of lawns and gardens. Minimize pesticide use outdoors, and water judiciously.

• Collect roof runoff with a rain barrel, and collect runoff from roofs and lawns in a rain garden. The goal is to keep most stormwater runoff on your property and out of storm drains. Allow water to infiltrate into the soil and not run off your property.

•

Clean up pet wastes, and don't put yard wastes into storm drains.

•

Use vegetation, mulch, or gravel to keep soil in place so it doesn't erode.

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• Have your septic tank inspected every three to five years. Be concerned if there is a smell of sewage or wetness or lush grass around your leach field.

• If you have a pond or stream on your property, leave natural vegetation around the water, and use plantings to discourage geese.

Fig. 1.2.8. A nice garden, irrigated with the recycled water A rain garden at the Holy Nativity Lutheran Church in Wenonah, NJ. Runoff drains to the garden which is planted with water-tolerant plants. The water slowly infiltrates into soil, allowing pollutants to be removed by plants and microbes. Photo: Christine Boyajian, Rutgers Cooperative Extension Water Resources Program. 

1.2.2.6 Eutrophication (Greek: eutrophia—healthy, adequate nutrition, development; German: Eutrophie) or more precisely hypertrophication, is the ecosystem response to the addition of artificial or natural substances, such as nitrates and phosphates through fertilizers or sewage, to an aquatic system. The organic substances nutrients given to the water body by wastewater disposal are food for the lower microorganisms which are growing up with high rates, consuming the dissolved oxygen, against the upper organisms . The result is the damage of ecology and equilibrium, with a development of lower microbes and death to upper organisms, resulting in the damage to ecological cycle. Many ecological effects can arise from stimulating primary production, but there are three particularly troubling ecological impacts: decreased biodiversity, changes in species composition and dominance, and toxicity effects.

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Impacts of Eutrophication: 

Increased biomass of phytoplankton

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Toxic or inedible phytoplankton species

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Increases in blooms of gelatinous zooplankton

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Increased biomass of benthic and epiphytic algae

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Changes in macrophyte species composition and biomass

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Decreases in water transparency (increased turbidity)

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Colour, smell, and water treatment problems

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Dissolved oxygen depletion

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Increased incidences of fish kills

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Loss of desirable fish species

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decreased biodiversity

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Reductions in harvestable fish and shellfish

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Decreases in perceived aesthetic value of the water body

http://en.wikipedia.org/wiki/Eutrophication#Ecological_effects 1.2.2.7. Prevention Of Pollution The operator's main job is to protect the many users of receiving waters. As an operator, you must do the best you can to remove any substances that will unreasonably affect these users.

Many people think any discharge of waste to a body of water is pollution.

However, with our present system of using water to carry away the waste products of homes and industries, it would be impossible and perhaps unwise to prohibit the discharge of all wastewater to oceans, streams, and groundwater basins. Today's technology is capable of treating wastes in such a manner that existing or potential receiving water uses are not unreasonably affected. Definitions of pollution include any interference with the beneficial reuse of water or failure to meet water quality requirements. Any questions or comments regarding this definition must be settled by the appropriate enforcement agency.

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1.2.2.8 Types Of Waste Discharges The waste discharge that first comes to mind in any discussion of stream pollution is the discharge of domestic wastewater. Wastewater contains a large amount of ORGANIC WASTE.2 Industry also contributes substantial amounts of organic waste.

Some of these organic industrial wastes come from vegetable and fruit packing; dairy processing; meat packing; tanning; and processing of poultry, oil, paper and fiber (wood), and many other industries. All organic materials have one thing in common—they all contain carbon.

Another classification of wastes is INORGANIC WASTES.3 Domestic wastewater contains inorganic material as well asorganic, and many industries discharge inorganic wastes that add to the mineral content of receiving waters. For instance, a discharge of salt brine (sodium chloride) from water softening will increase the amount of sodium and chloride in the receiving waters. Some industrial wastes may introduce inorganic substances such as chromium or copper, which are very toxic to aquatic life. Other industries (such as gravel washing plants) discharge appreciable amounts of soil, sand, or grit, which also may be classified as inorganic wastes.

There are two other major types of wastes that do not fit either the organic or inorganic classification. These are heated (thermal) wastes and radioactive wastes.

Waters with temperatures exceeding the requirements of the enforcing agency may come from cooling processes used by industry and from thermal power stations generating electricity. Radioactive wastes are usually controlled at their source, but could come from hospitals, research laboratories, and nuclear power plants.

1.2.2.9 Effects Of Waste Discharges Certain substances not removed by wastewater treatment processes can cause problems in receiving waters. This section reviews some of these substances and discusses why they should be treated.

1.2.2.9.1 Sludge and Scum If certain wastes (including domestic wastewater) do not receive adequate treatment, large amounts of solids may accumulate on the banks of the receiving waters, or they may settle to the bottom to form sludge deposits or float to the surface and form rafts of scum. Sludge deposits and scum are not only unsightly but, if they contain organic material, they may also cause oxygen depletion and be a source of odors. PRIMARY TREATMENT* units in the wastewater treatment plant are designed and operated to remove the sludge and scum before they reach the receiving waters.

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Fig. 1.2.9. Sewage contamination of a small stream.

1.2.2.9.2 Oxygen Depletion Most living creatures need oxygen to survive, including fish and other aquatic life.

Although most streams and other surface waters contain less than 0.001% dissolved oxygen (10 milligrams of oxygen per liter of water, or 10 mg/L), most fish can thrive if there are at least 5 mg/L and other conditions are favorable. When oxidizable wastes are discharged to a stream, bacteria begin to feed on the waste and decompose or break down the complex substances in the waste into simple chemical compounds. These bacteria also use dissolved oxygen (similar to human respiration or breathing) from the water and are called AEROBIC BACTERIA. As more organic waste is added, the bacteria reproduce rapidly; and as their population increases, so does their use of oxygen. Where waste flows are high, the population of bacteria may grow large enough to use the entire supply of oxygen from the stream faster than it can be replenished by natural diffusion from the atmosphere. When this happens, fish and most other living things in the stream that require dissolved oxygen die.

Therefore, one of the principal objectives of wastewater treatment is to prevent as much of this "oxygen-demanding" organic material as possible from entering the receiving water. The treatment plant actually removes the organic material the same way a stream does, but it accomplishes the task much more efficiently by removing the wastes from the wastewater. SECONDARY TREATMENT units are designed and operated to use natural organisms such as bacteria in the plant for the STABILIZATION and removal of organic material.

Another effect of oxygen depletion, in addition to the killing of fish and other aquatic life, is the problem of odors. When all the dissolved oxygen has been removed, ANAEROBIC BACTERIA begin to use the oxygen that is combined chemically with

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other elements in the form of chemical compounds, such as sulfate (sulfur and oxygen), which are also dissolved in the water. When anaerobic bacteria remove the oxygen from sulfur compounds, hydrogen sulfide (H2S), which has a rotten egg odor, is produced. This gas is not only very odorous, but it also erodes (corrodes) concrete and can discolor and remove paint from homes and structures. Hydrogen sulfide also may form explosive mixtures with air and is a toxic gas capable of paralyzing your respiratory system. Other products of anaerobic decomposition (putrefaction) also can be objectionable.

The disposal of wastewater (BOD) typically causes a decrease in O2, followed by a gradual increase close to the dissolved oxygen (D.O.) saturation concentration.

The organic substances nutrients given to the water body by wastewater disposal are food for the lower microorganisms which are growing up with high rates, consuming the dissolved oxygen, against the upper organisms (eutrophication etc.).

The dissolved oxygen (D.Ο.) will take a minimum value, until the point where and the moment when the oxygenation rate is equal or more with the oxygen consumption.

All this event is described by the Streeter-Phelps equation and model So, all the seasonal ecological equilibrium in the water body is spoiled. This change will damage the health of the system and the conditions in the water body will get to ecologically better conditions as soon as the oxygen will be increased to adequate level.

The time and the length of the river for recovering the problem with reoxygenation of the river (or the water body) are critical parameters for the survive of the upper forms of life and the ecological equilibrium in the river (or the water body) The oxygen deficit and the reoxygenation process, are described by Streeter-Phelps model:

More…

1.Do content is one of the most widely used indicators of overall ecological health of a body of water • fish need 4 to 5 mg/L to survive • under anaerobic conditions, undesirable (smelly) microbes can take over • many factors affect the DO level 1.

If a river was healthy before we began discharging wastewater, a significant factor in its continued health or illness is the BOD added to it by wastewater At the outfall, BOD of the river/wastewater mixture (L0) is given by:

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a.

Note: We found this formula earlier when we used a mass balance model for mixing b.

This BOD is comparable to what we have in our stoppered bottle at the beginning of our BOD test As time passes (ie, the water moves downstream) the oxygen content of the river water is consumed in just the same way oxygen is consumed in the test Remember that BOD (Lt) in a test bottle at time t is given by: Lt = L0e-kDt This formula holds in the river too (kD is the deoxygenation constant that we previously just called k; it can be adjusted for temperature using kT = k20q T-20) If we know an average velocity of flow, we can calculate the BOD for a given distance downstream 1.

We are probably more interested in how much DO remains, which depends both on the rate of deoxygenation (as in our bottle) and on the rate of reoxygenation or reaeration (which doesn’t occur in our bottle) o The rate of reaeration, rR, is given by: rR = -kR*D with kR = reaeration time constant D = DO deficit = DOs-DO The reaeration time constant can be estimated from Table 3-2, or calculated by: kR,20°C = 3.9u1/2/H3/ u = average stream velocity H = average stream depth

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Water body

Ranges of kR at 20°C, base e

Small ponds and backwaters

0.1-0:23

Sluggish streams and large lakes

0.23-0.35

Large streams of low velocity

0.35-0.46

Large streams of normal velocity

0.46-0.69

Swift streams

0.69-1.15

Rapids and waterfalls

Greater than 1.15

Source: Peavy, Rowe and Tchobanoglous, 1985

o To start with, the waste has some oxygen deficit which causes an initial DO deficit in the stream o Water can only hold so much oxygen (DOsat), depending on the the water temperature o Calculate the initial dissolved oxygen (DO0) using the same formula we used for L0 above o

Subtracting that from the initial DOsat:

D0 = DOsat - DO0 The DO at any point downstream depends on these competing processes: rate of deficit increase = rate of deoxygenation - rate of reaeration This gives us a differential equation with the solution:

This is the Streeter-Phelps oxygen-sag curve formula Note that for a constant stream cross-section, t=x/u (with u=stream velocity); therefore:

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1.If we want to plot DO versus distance downstream (that’s what I’m used to seeing) we need to subtract D from Ds at each point 2.To start with, DO is being depleted faster than it can be replenished As long as this occurs, the DO of the stream will continue to drop Since the BOD is decreasing as time goes on, at some point, the rate of deoxygenation decreases to just the rate of reaearation At this point (called the critical point) the DO reaches a minimum Downstream of the critical point, reaeration occurs faster than deoxygenation, so the DO increases Using calculus and the Streeter-Phelps equation we get:

An application of the Streeter-Phelps Model Example: Wastewater mixes with a river resulting in a BOD = 10.9 mg/L,

DO = 7.6 mg/L

The mixture has a temp. = 20 C Deoxygenation const.= 0.2 day-1 Average flow = 0.3 m/s,

Average depth = 3.0 m

DO saturated = 9.1 mg/L Find the time and distance downstream at which the oxygen deficit is a maximum?

Find the minimum value of DO? Initial Deficit , Do = 9.1 – 7.6 = 1.5 mg/L

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Estimate the reaeration constant

Calculate the time at which the maximum deficit is reached, with t c: tc  

 k  DOo ( k 2  k1 )   1 ln  2 1   k 2  k1  k1  k1 Lo  

 0.41  1.5(0.41  0.2)   1 ln  1  (0.41  0.2)  0.2  0.2  10.9  

 2.67days x c  vt c  0.3m / s  86,400s / day  2.67days  69,300m

The maximum DO deficit is:

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1.2.2.9.3 Human Health Up to now, we have discussed the physical or chemical effects that a waste discharge may have on the uses of water. More important, however, may be the effect on human health through the spread of disease-causing bacteria and viruses. Initial efforts to control human wastes evolved from the need to prevent the spread of diseases. Although untreated wastewater contains many billions of bacteria per gallon, most of these are not harmful to humans, and some are even helpful in wastewater treatment processes. However, humans who have a disease that is caused by bacteria or viruses may discharge some of these harmful organisms in their body wastes. Many serious outbreaks of communicable diseases have been traced to direct contamination of drinking water or food supplies by the body wastes from a human disease carrier.

Other diseases that could be spread by wastewater include Some known examples of diseases that may be spread through wastewater discharges are giardiasis (giardia) and cryptosporidiosis (crypto). Fortunately, the bacteria that grow in the intestinal tract of diseased humans are not likely to find the environment in the wastewater treatment plant or receiving waters favorable for their growth and reproduction. Although many PATHOGENIC ORGANISMS™ are removed by natural die-off during the normal treatment processes, sufficient numbers can remain to cause a threat to any downstream use involving human contact or consumption. If such uses exist downstream, the treatment plant must also include a DISINFECTION^ process.

The disinfection process most often used is the addition of chlorine. In most cases, proper chlorination of a well-treated waste will result in essentially a complete kill of the pathogenic organisms. Operators must realize, however, that the breakdown or malfunction of equipment could result in the discharge at any time of an effluent that contains pathogenic bacteria. To date, no one working in the wastewater collection or treatment field is known to have become infected by the AIDS virus due to conditions encountered while working on the job. Good personal hygiene is an operator's best defense against infections and diseases.

1.2.2.9.4 Other Effects Some wastes adversely affect the clarity and color of the receiving waters, making them unsightly and unpopular for recreation.

Many industrial wastes are highly acid or alkaline (basic), and either condition can interfere with aquatic life, domestic use, and other uses. An accepted measurement of a waste's acidic or basic condition is its pH.12 Before wastes are discharged, they should have a pH similar to that of the receiving water.

Waste discharges may contain toxic substances, such as heavy metals (lead, mercury, cadmium, and chromium) or cyanide, which may affect the use of the receiving water for domestic purposes or for aquatic life. Plant effluents chlorinated for disinfection purposes may have to be dechlorinated to protect receiving waters from the toxic effects of residual chlorine. Taste- and odor-producing substances may reach levels in the receiving water that are readily detectable in drinking water or in the flesh of fish.

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Treated wastewaters contain NUTRIENTS'3 capable of encouraging excess ALGAEU and plant growth in receiving waters. These growths hamper domestic, industrial, and recreational uses. Conventional wastewater treatment plants do not remove a major portion of the nitrogen and phosphorus nutrients.

NATURAL CYCLES When the treated wastewater from a plant is discharged into RECEIVING WATERS™ such as streams, rivers, or lakes, natural cycles in the aquatic (water) environment may become upset. Whether any problems are caused in the receiving waters depends on the following factors: 1. Type or degree of treatment 2. Size of flow from the treatment plant 3. Characteristics of wastewater from the treatment plant 4. Amount of flow in the receiving stream or volume of receiving lake that can be used for dilution 5. Quality of the receiving waters 6. Amount of mixing between the EFFLUENT" and receiving waters 7. Uses of the receiving waters Natural cycles of interest in wastewater treatment include the natural purification cycles such as the cycle of water from evaporation or TRANSPIRATION™ to condensation to precipitation to runoff and back to evaporation, the life cycles of aquatic organisms, and the cycles of nutrients. These cycles are occurring continuously in wastewater treatment plants and in receiving waters at different rates depending on environmental conditions. Treatment plant operators control and accelerate these cycles to work for their benefit in treatment plants and in receiving waters rather than have these cycles cause plant operational problems and disrupt downstream water uses.

NUTRIENT CYCLES™ (Figure ........) are a special type of natural cycle because of the sensitivity of some receiving waters to nutrients. Important nutrients include carbon, hydrogen, oxygen, sulfur, nitrogen, and phosphorus. All of the nutrients have their own cycles, yet each cycle is influenced by the other cycles. These nutrient cycles are very complex and involve chemical changes in living organisms.

To illustrate the concept of nutrient cycles, a simplified version of the nitrogen cycle will be used as an example (Figure 2.2). A wastewater treatment plant discharges nitrogen in the form of nitrate (N03-), in the plant effluent to the receiving waters. Algae take up the nitrate and produce more algae. The algae are eaten by fish, which convert the nitrogen to amino acids, urea, and organic residues. If the fish die and sink to the bottom, these nitrogen compounds can be converted to ammonium (NH4+). In the presence of dissolved oxygen and special bacteria, the

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ammonium is converted to nitrite (N02-) then to nitrate (N03-), and finally the algae can take up the nitrate and start the cycle all over again.

If too much nitrogen is discharged to receiving waters, too many algae could be produced. Water with excessive algae can be unsightly. Bacteria decomposing dead algae from occasional die-offs can deplete the dissolved oxygen and cause a fish kill.

Thus, the nitrogen cycle has been disrupted, as well as the other nutrient cycles. If no dissolved oxygen is present in the water, the nitrogen compounds are converted to ammonium (NH4+) , the carbon compounds to methane (CH4), and the sulfur compounds to hydrogen sulfide (H2S). Ammonia (NH3) and hydrogen sulfide are odorous gases. Under these conditions the receiving waters are SEPTIC20; they stink and look terrible. Throughout this manual, you will be provided information on how to control these nutrient cycles in your treatment plant in order to treat wastes and to control odors, as well as to protect receiving waters.

Fig. 1.2.10. Simplified illustration of Nitrogen Cycle NPDES stands for National Pollutant Discharge Elimination System. NPDES permits are required by the Federal Water Pollution Control Act Amendments of 1972 with the intent of making the nation's waters suitable for swimming and for fish and wildlife. The permits regulate discharges into US waterways from all point sources of pollution, including industries, municipal wastewater treatment plants, sanitary landfills, large animal feedlots, and return irrigation flows. An industry discharging into municipal collection and treatment systems need not obtain a permit but must meet certain specified pretreat-ment standards. These permits may outline a schedule of compliance for a wastewater treatment facility such as dates for the completion of plant design, engineering, construction, or treatment process

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changes. Instructions for completing NPDES reporting forms and the necessary forms are available from the regulatory agency issuing the permit.

Your main concern as an operator is the effluent (discharge) limitations specified in the NPDES permit for your plant. The permit may specify monthly average and maximum levels of suspended solids, BIOCHEMICAL OXYGEN DEMAND (BOD), and the most probable number (MPN) of COLI-FORM group bacteria. Larger plants must report effluent temperatures because of the impact of temperature changes on natural cycles. Also, average and maximum flows may be identified as well as an acceptable range of pH values. Almost all effluents are expected to contain virtually no substances that would be toxic to organisms in the receiving waters. NPDES permits have effluent limit restrictions on toxic substances. The NPDES permit will specify the frequency of collecting samples and the methods of reporting the results.

Details on how to comply with NPDES permits will be provided throughout this manual.

1.2.3. Main Sewerage systems 1.2.3.1 Sewers' Design History The earliest covered sewers uncovered by archaeologists are in the regularly planned cities of the Indus Valley Civilization. In ancient Greece, from Minoan age, were found by archaeologists covered sewers and open channels for storm waters. In ancient Rome, the Cloaca Maxima, considered a marvel of engineering, discharged into the Tiber. The earliest covered sewers uncovered by archaeologists are in the regularly planned cities of the Indus Valley Civilization. In ancient Rome, the Cloaca Maxima, considered a marvel of engineering, disgorged into the Tiber. During the Zhou Dynasty in ancient China, sewers existed in various cities such as Linzi. In medieval European cities, small natural waterways used for carrying off wastewater were eventually covered over and functioned as sewers. London's River Fleet is such a system. Open drains along the center of some streets were known as "kennels" (i.e., canals, channels).

Many cities that installed sewage collection systems in the early 20th century, or earlier, used single-pipe systems that collect both sewage and urban runoff from streets and roofs. This type of collection system is referred to as a combined sewer system (CSS). The cities' rationale when these systems were built was that it would be cheaper to build just a single system. Most cities at that time did not have sewage treatment plants, so there was no perceived public health advantage in constructing a separate storm sewer system 1.2.3.2 Combined sewer system is a type of sewer system that collects sanitary sewage and stormwater runoff in a single pipe system. Combined sewers can cause serious water pollution problems

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due to combined sewer overflows, which are caused by large variations in flow between dry and wet weather. This type of sewer design is no longer used in building new communities, but many older cities continue to operate combined sewers. A combined sewer overflow (CSO) is the discharge of wastewater and stormwater from a combined sewer system directly into a river, stream, lake, or ocean. Overflow frequency and duration varies both from system to system, and from outfall to outfall, within a single combined sewer system. Some CSO outfalls discharge infrequently, while others activate every time it rains. During heavy rainfall when the stormwater exceeds the sanitary flow, the CSO is diluted.

The storm water component contributes a significant amount of pollutants to CSO. Each storm is different in the quantity and type of pollutants it contributes. For example, storms that occur in late summer, when it has not rained for a while, have the most pollutants. Pollutants like oil, grease, fecal coliform from pet and wildlife waste, and pesticides get flushed into the sewer system. In cold weather areas, pollutants from cars, people and animals also accumulate on hard surfaces and grass during the winter and then are flushed into the sewer systems during heavy spring rains.

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Fig. 1.2.11. Combined sewer, during a storm, with detail in overflow wire

Fig. 1.2.12. Simplified Combined sewers during dry and wet weather 1.2.3.3. Sanitary sewerage (or foul sewer) A sanitary sewer (also called a foul sewer) is a separate underground carriage system specifically for transporting sewage from houses and commercial buildings to treatment or disposal. Sanitary sewers serving industrial areas also carry industrial wastewater. The 'system of sewers' is called sewerage.

Sanitary sewers are operated separately and independently of storm drains, which carry the runoff of rain and other water which wash into city streets All sewers deteriorate with age, but infiltration/inflow is a problem unique to sanitary sewers, since both combined sewers and storm drains are sized to carry these contributions. Holding infiltration to acceptable levels requires a higher standard of maintenance than necessary for structural integrity considerations of combined sewers. A comprehensive construction inspection program is required to prevent inappropriate connection of cellar, yard, and roof drains to sanitary sewers. The probability of inappropriate connections is higher where combined sewers and sanitary sewers are found in close proximity, because construction personnel may not recognize the difference. Many older cities still use combined sewers while adjacent suburbs were built with separate sanitary sewers. In areas where "wet volume" is many times larger than "dry volume" the Combined sewer system has been replaced with the sanitary system , operating separate For decades, when sanitary sewer pipes got cracks or other damage, the only choice was the expensive operation of digging up the damaged pipe and replacing it, usually requiring the street to be repaved afterwards. In the mid-1950s a unit was invented where two units at each end with a special cement mixture in between was pulled from one manhole cover to the next, coating the pipe with the cement under high pressure which then dried at a fast rate, sealing all cracks and breaks in the pipe.

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Fig. 1.2.13. Simplified Sanitary sewers and storm sewers seperated

Fig. 1.2.14. Sanitary sewers, cracked and infiltration problems

1.2.3.4. Pressure Sewers (from EPA Wastewater Technology Fact Sheet, Sewers, Pressure) Pressure sewers are particularly adaptable for rural or semi-rural communities where public contact with effluent from failing drain fields presents a substantial health concern. Since the mains for pressure sewers are, by design, watertight, the

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pipe connections ensure minimal leakage of sewage. This can be an important consideration in areas subject to groundwater contamination.

Pressure sewer systems are to be used in smaller, remote villages and where it is impractical or uneconomical to use a gravity sewer system. Pressure sewerage systems have been used extensively throughout the USA and Europe for about 30 years. The systems are an effective solution for small areas and where conventional systems are impractical such as rocky, hilly and/or water charged terrain or other circumstances considered warranted.

Pressure sewer systems are an economical and environmentally-friendly way of collecting, transporting and disposing of wastewater from households. Once installed, the only visible parts of the pressure sewer system are the tank lid and control panel, as shown in the photograph above.

The two main pressure sewer technologies available today are septic tank effluent pump (STEP) and grinder pump (GP). Both technologies use small diameter PVC or HDPE sewer mains, normally 2-8 inch diameter, that follow the contour of the land, to convey the wastewater to a treatment facility or to a larger sewer main in a neighboring municipality, without the need for deep excavations, manholes, or lift stations.

1.2.3.5. Effluent sewers system (septic tank effluent pump) In STEP systems, wastewater flows into a conventional septic tank to capture solids.

The liquid effluent flows to a holding tank containing a pump and control devices.

The effluent is then pumped and transferred for treatment. Retrofitting existing septic tanks in areas served by septic tank/drain field systems would seem to present an opportunity for cost savings, but a large number (often a majority) must be replaced or expanded over the life of the system because of insufficient capacity, deterioration of concrete tanks, or leaks.

The septic tank, filter, and pump at each house remove settleable solids, and the effluent flows through the collection line to the recirculating fixed-film treatment system. This system uses simple technology with low operation and maintenance costs to produce an effluent that is often higher quality than effluent that has undergone traditional secondary treatment. For example, in the type of STEP system described above, settling solids in the individual septic tanks enables the use of the smaller-diameter collection line, which is much quicker and easier to install than the traditional 6- to 8-in. diameter (150- to 200-mm diameter) collection piping. The larger pipe and more invasive installation lead to much higher costs per meter of line and much greater disturbance to the route (see Figure 1.2.15).

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Fig. 1.2.15. STEP sewerage system Grinder sewers (from EPA Wastewater Technology Fact Sheet, Sewers, Pressure) In a GP system, sewage flows to a vault where a grinder pump grinds the solids and discharges the sewage into a pressurized pipe system. GP systems do not require a septic tank but may require more horsepower than STEP systems because of the grinding action. A GP system can result in significant capital cost savings for new areas that have no septic tanks or in older areas where many tanks must be replaced or repaired. Figure 1.2.15 shows a typical septic tank effluent pump, while Figure 1.2.16 shows a typical grinder pump used in residential wastewater treatment.

They are often used in areas when the landscape is either very hilly or very flat, in areas which regularly flood or have high water tables, or where it is impractical to install other types of sewerage systems. A pressure sewer system is made up of a network of fully sealed pipes which are fed by pumping units located at each connected property. The pumping unit processes the property wastewater and transfers it to the pressure sewer located in the street via a small pipeline within the property. The pressure sewer forms part of the overall pipe network which ultimately transfers the wastewater to the nearest wastewater treatment facility this could be within the surrounding area or many kilometres away.

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Fig 1.2.16. A pressure sewer unit, in section and final looking in the garden

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Fig 1.2.17. A pressure sewer unit, installed, in operation This system requires only shallow trenches and relatively smaller 40mm diameter piping, within the property boundary and up to 160mm diameter in the street.

A pressure sewer system is made up of a network of fully sealed pipes which are fed by pumping units located at each connected property. The pumping unit processes the property wastewater and transfers it to the pressure sewer located in the street via a small pipeline within the property. The pressure sewer forms part of the overall pipe network which ultimately transfers the wastewater to the nearest wastewater treatment facility this could be within the surrounding area or many kilometers away.

Once installed, the only visible parts of the pressure sewer system are the tank lid and control panel, as shown in the photograph above.

What components make up a pressure sewer system (Grinder sewers) ?

The pressure sewer system on your property is made up of four key elements, as shown in the diagram below.

1. Pumping Unit (Goulburn Valley Water) This includes a small pump, storage tank and level monitors which are all installed underground so that only the top of the storage tank (or lid) is visible.

2. Boundary Valve Kit (Goulburn Valley Water) Ensures that wastewater which is already in the pressure sewer cannot re-enter your property and enables maintenance staff to isolate you from the system in the event of an emergency.

3. House Service Line (Property Owner) This is a small diameter pipe (not dissimilar to a large sprinkler system pipe) which connects your property drain to the pumping unit on your property.

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4. Control Panel (Goulburn Valley Water)

More…

The choice between GP and STEP systems depends on three main factors, as described below: Cost: On-lot facilities, including pumps and tanks, will account for more than 75 percent of total costs, and may run as high as 90 percent. Thus, there is a strong motivation to use a system with the least expensive on-lot facilities. STEP systems may lower on-lot costs because they allow some gravity service connections due to the continued use of a septic tank. In addition, a grinder pump must be more rugged than a STEP pump to handle the added task of grinding, and, consequently, it is more expensive. If many septic tanks must be replaced, costs will be significantly higher for a STEP system than a GP system. Downstream Treatment: GP systems produce a higher TSS that may not be acceptable at a downstream treatment facility.

Low Flow Conditions: STEP systems will better tolerate low flow conditions that occur in areas with highly fluctuating seasonal occupancy and those with slow build out from a small initial population to the ultimate design population. Thus, STEP systems may be better choices in these areas than GP systems.

ADVANTAGES AND DISADVANTAGES Advantages Pressure sewer systems that connect several residences to a “cluster” pump station can be less expensive than conventional gravity systems. On-property facilities represent a major portion of the capital cost of the entire system and are shared in a cluster arrangement.

This can be an economic advantage since on-property components are not required until a house is constructed and are borne by the homeowner. Low front-end investment makes the present-value cost of the entire system lower than that of conventional gravity sewerage, especially in new development areas where homes are built over many years.

Because wastewater is pumped under pressure, gravity flow is not necessary and the strict alignment and slope restrictions for conventional gravity sewers can be relaxed. Network layout does not depend on ground contours: pipes can be laid in any location and extensions can be made in the street right-of-way at a relatively small cost without damage to existing structures.

Other advantages of pressure sewers include: Material and trenching costs are significantly lower because pipe size and depth requirements are reduced. Low-cost clean outs and valve assemblies are used rather than manholes and may be spaced further apart than manholes in a conventional system. Infiltration is reduced, resulting in reductions in pipe size. The user pays for the electricity to operate the pump unit. The resulting increase in electric bills is small and may replace municipality or community bills for central pumping eliminated by the pressure

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system. Final treatment may be substantially reduced in hydraulic and organic loading in STEP systems. Hydraulic loadings are also reduced for GP systems.

Because sewage is transported under pressure, more flexibility is allowed in siting final treatment facilities and may help reduce the length of outfall lines or treatment plant construction costs.

Disadvantages Requires much institutional involvement because the pressure system has many mechanical components throughout the service area. The operation and maintenance (O&M) cost for a pressure system is often higher than a conventional gravity system due to the high number of pumps in use. However, lift stations in a conventional gravity sewer can reverse this situation. Annual preventive maintenance calls are usually scheduled for GP components of pressure sewers.

STEP systems also require pump-out of septic tanks at two to three year intervals.

Public education is necessary so the user knows how to deal with emergencies and how to avoid blockages or other maintenance problems. The number of pumps that can share the same downstream force main is limited. Power outages can result in overflows if standby generators are not available. Life cycle replacement costs are expected to be higher because pressure sewers have a lower life expectancy than conventional systems. Odors and corrosion are potential problems because the wastewater in the collection sewers is usually septic. Proper ventilation and odor control must be provided in the design and non-corrosive components should be used. Air release valves are often vented to soil beds to minimize odor problems and special discharge and treatment designs are required to avoid terminal discharge problems.

DESIGN CRITERIA Many different design flows can be used in pressure systems. When positive displacement GP units are used, the design flow is obtained by multiplying the pump discharge by the maximum number of pumps expected to be operating simultaneously. When centrifugal pumps are used, the equation used is Q= 20 + 0.5D, where Q is the flow in gpm and D is the number of homes served. The operation of the system under various assumed conditions should be simulated by computer to check design adequacy. No allowances for infiltration and inflow are required. No minimum velocity is generally used in design, but GP systems must attain three to five feet per second at least once per day. A Hazen-Williams coefficient, (C) = 130 to 140, is suggested for hydraulic analysis.

Pressure mains generally use 50 mm (2 inch) or larger PVC pipe (SDR 21) and rubberring joints or solvent welding to assemble the pipe joints. High-density polyethylene (HDPE) pipe with fused joints is widely used in Canada. Electrical requirements, specially for GP systems, may necessitate rewiring and electrical service upgrading in the service area. Pipes are generally buried to at least the winter frost penetration depth; in far northern sites insulated and heat-traced pipes are generally buried at a minimal depth. GP and STEP pumps are sized to accommodate the hydraulic grade requirements of the system. Discharge points must use drop inlets to minimize odors

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and corrosion. Air release valves are placed at high points in the sewer and often are vented to soil beds. Both STEP and GP systems can be assumed to be anaerobic and potentially odorous if subjected to turbulence (stripping of gases such as H2S).

Table ‌.. Relative Characteristics Of Alternative Sewers

PERFORMANCE STEP When properly installed, septic tanks typically remove about 50 percent of BOD, 75 percent of suspended solids, virtually all grit, and about 90 percent of grease, reducing the likelihood of clogging. Also, wastewater reaching the treatment plant will be weaker than raw sewage. Typical average values of BOD and TSS are 110 mg/L and 50 mg/L, respectively. On the other hand, septic tank effluent has virtually zero dissolved oxygen.

Primary sedimentation is not required to treat septic tank effluent. The effluent responds well to aerobic treatment, but odor control at the headworks of the treatment plant should receive extra attention.

The small community of High Island, Texas, was concerned that septic tank failures were damaging a local area frequented by migratory birds. Funds and materials were secured from the EPA, several state agencies, and the Audubon Society to replace the undersized septic tanks with larger ones equipped with STEP units and low pressure sewerage ultimately discharging to a constructed wetland. This system is expected to achieve an effluent quality of less than 20 mg/L each of BOD and TSS, less than 8 mg/L ammonia, and greater than 4 mg/L dissolved oxygen (Jensen 1999).

In 1996, the village of Browns, Illinois, replaced a failing septic tank system with a STEP system discharging to low pressure sewers and ultimately to a recirculating gravel filter. Cost was a major concern to the residents of the village, who were used to average monthly sewer bills of $20. Conditions in the village were poor for conventional sewer systems, making them prohibitively expensive. An alternative low pressure-STEP system averaged only $19.38 per month per resident, and eliminated the public health hazard caused by the failed septic tanks (ICAA, 2000).

GP Treatment

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The wastewater reaching the treatment plant will typically be stronger than that from conventional systems because infiltration is not possible. Typical design average concentrations of both BOD and TSS are 350 mg/L (WPCF, 1986). GP/low pressure sewer systems have replaced failing septic tanks in Lake Worth, Texas (Head, et. al., 2000); Beach Drive in Kitsap County, Washington (Mayhew and Fitzwater, 1999); and Cuyler, New York (Earle, 1998). Each of these communities chose alternative systems over conventional systems based on lower costs and better suitability to local soil conditions.

OPERATION AND MAINTENANCE Routine operation and maintenance requirements for both STEP and GP systems are minimal. Small systems that serve 300 or fewer homes do not usually require a fulltime staff. Service can be performed by personnel from the municipal public works or highway department. Most system maintenance activities involve responding to homeowner service calls usually for electrical control problems or pump blockages.

STEP systems also require pumping every two to three years. The inherent septic nature of wastewater in pressure sewers requires that system personnel take appropriate safety precautions when performing maintenance to minimize exposure to toxic gases, such as hydrogen sulfide, which may be present in the sewer lines, pump vaults, or septic tanks. Odor problems may develop in pressure sewer systems because of improper house venting. The addition of strong oxidizing agents, such as chlorine or hydrogen peroxide, may be necessary to control odor where venting is not the cause of the problem.

Generally, it is in the best interest of the municipality and the homeowners to have the municipality or sewer utility be responsible for maintaining all system components. General easement agreements are needed to permit access to on-site components, such as septic tanks, STEP units, or GP units on private property.

COSTS Pressure sewers are generally more cost-effective than conventional gravity sewers in rural areas because capital costs for pressure sewers are generally lower than for gravity sewers. While capital cost savings of 90 percent have been achieved, no universal tatement of savings is possible because each site and system is unique.

Table 1 presents a generic comparison of common characteristics of sanitary sewer systems that should be considered in the initial decision-making process on whether to use pressure sewer systems or conventional gravity sewer systems. Table 2 presents data from recent evaluations of the costs of pressure sewer mains and appurtenances (essentially the same for GP and STEP), including items specific to each type of pressure sewer. Purchasing pumping stations in volume may reduce costs by up to 50 percent. The linear cost of mains can vary by a factor of two to three, depending on the type of trenching equipment and local costs of high-quality backfill and pipe. The local geology and utility systems will impact the installation cost of either system. The homeowner is responsible for energy costs, which will vary from $1.00 to $2.50/month for GP systems, depending on the horsepower of the unit. STEP units generally cost less than $1.00/month. Preventive maintenance should be performed annually for each unit, with monthly maintenance of other mechanical components. STEP systems require periodic pumping of septic tanks.

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Total O&M costs average $100-200 per year per unit, and include costs for troubleshooting, inspection of new installations, and responding to problems. Mean time between service calls (MTBSC) data vary greatly, but values of 4 to 10 years for both GP and STEP units are reasonable estimates for quality installations.

REFERENCES Other Related Fact Sheets Other EPA Fact Sheets can be found at the following web address: http://www.epa.gov/owm/mtb/mtbfact.htm 1. Barrett, Michael E. and J. F. Malina, Jr., Sep. 1, 1991. Technical Summary of Appropriate Technologies for Small Community Wastewater Treatment Systems, The University of Texas at Austin.

2. Barrett, Michael E. and J. F. Malina, Jr., Sep. 1, 1991. Wastewater Treatment Systems for Small Communities: A Guide for Local Government Officials, The University of Texas at Austin.

3. Earle, George, 1998. Low Pressure Sewer Systems: The Low Cost Alternative to Gravity Sewers.

4. Falvey, Cathleen, 2001. Pressure Sewers Overcome Tough Terrain and Reduce Installation Costs. Small Flows Quarterly, National Small Flows Clearinghouse.

5. F.E. Meyers Company, 2000. Diagram of grinder pump provided to Parsons ngineering Science.

6. Gidley, James S., Sep. 1987. Case Study Number 12: Augusta, Maine, Grinder Pump Pressure Sewers. National Small Flows Clearinghouse.

7. Head, Lee A., Mayhall, Madeline R.,Tucker, Alan R., and Caffey, Jeffrey E., 2000.

Low Pressure Sewer System Replaces Septic System in Lake Community. http://www.eone.com/sewer/resources/resource01/content.html 8. Illinois Community Action Association, 2000. Alternative Wastewater Systems in Illinois. http://www.icaanet.com/rcap/aw_pamphlet.htm.

9. Jensen, Ric., August 1999. Septic Tank Effluent Pumps, Small Diameter Sewer, Will Replace Failing Septic Systems at Small Gulf Coast Community. Texas On-Site I n s i g hts,Vol.8,No.3. http://twri.tamu.edu/./twripubs/Insights/v8n3/a rticle-1.html.

10. Mayhew, Chuck and Richard Fitzwater, September 1999. Grinder Pump Sewer System Saves Beach Property. Water Engineering and Management.

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1.2.3.6 Vacuum Sewers (From Wikipedia, the free encyclopedia) A vacuum sewer system uses the differential pressure between atmospheric pressure and a partial vacuum maintained in the piping network and vacuum station collection vessel. This differential pressure allows a central vacuum station to collect the wastewater of several thousand individual homes, depending on terrain and the local situation. Vacuum sewers take advantage of available natural slope in the terrain and are most economical in flat sandy soils with high ground water.

A vacuum sewer system is composed of: Collection chambers and vacuum valve units Monitoring system for collection chambers and vacuum valve units Vacuum sewer lines

Fig 1.2.18. Typical connection to Central vacuum station

Fig 1.2.19. Typical vacuum sewage system

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Fig 1.2.20. Typical vacuum station

More…

Vacuum technology is based on differential air pressure. Rotary vane vacuum pumps generate an operation pressure of -0.4 to -0.6 bar at the vacuum station, which is also the only element of the vacuum sewerage system that must be supplied with electricity. Interface valves that are installed inside the collection chambers work pneumatically. Any sewage flows by means of gravity into each house’s collection sump. After a certain fill level inside this sump is reached, the interface valve will open. The impulse to open the valve is usually transferred by a pneumatically (pneumatic pressure created by fill level) controlled controller unit. No electricity is needed to open or close the valve. The according energy is provided by the vacuum itself. While the valve is open, the resulting differential pressure between

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atmosphere and vacuum becomes the driving force and transports the wastewater towards the vacuum station. Besides these collection chambers, no other manholes, neither for changes in direction, nor for inspection or connection of branch lines, are necessary. High flow rates keep the system free of any blockages or sedimentation.

Vacuum sewer systems are considered to be free of ex- and infiltration which allows the usage even in water protection areas. For this reason, vacuum sewer lines may even be laid in the same trench as potable water lines (depending on local guidelines). The system supplier should certify his product to be used in that way. To achieve the condition of an infiltration-free system and therefore allowing to reduce the waste water amounts that need to be treated, water tight (PE material or similar) collection chambers should be used. Valve and collection sump (waste water) preferably should be physically separated (different chambers) in order to protect service personal against direct contact with waste water and to ensure longer life cycles (waste water is considered to be corrosive).

In order to ensure reliable transport, the vacuum sewer line is laid in a saw-tooth (length-) profile, which will be referred to more precisely afterwards. The whole vacuum sewers are filled with air at a pressure of -0.4 to -0.6 bar. The most important aspect for a reliable operation is the air-to-liquid ratio. When a system is well designed, the sewers contain only very small amounts of sewage. The air-toliquid ratio is usually maintained by "intelligent" controller units or valves that adjust their opening times according to the pressure in the system.

Considering that the vacuum idea relies on external energy for the transport of fluids, sewers can be laid in flat terrain and up to certain limits may also be countersloped. The saw-tooth profile keeps sewer lines shallow, lifts minimise trench depth (approx. 1.0 – 1.2 m). In this depth, expensive trenching, as it is the case for gravity sewers with the necessity to install continuously falling slopes of at least 0.5 - 1.0%, is avoided. Lifting stations are not required.

Once arrived in the vacuum collection tank at the vacuum station, the wastewater is pumped to the discharge point, which could be a gravity sewer or the treatment station directly. As the dwell time of the watewater inside the system is very short and the wastewater is continuously mixed with air, the sewage is kept fresh and any fouling inside the system is avoided (less H2S).

Advantages

    

Closed, pneumatically controlled system with a central vacuum station.

Electrical energy is only needed at this central station No sedimentation due to self-cleansing high velocities spooling and maintenance of the sewer lines is not necessary Manholes are not required Usually only a single vacuum pump station is required rather than multiple stations found in gravity and low pressure networks. This frees up land, reduces energy costs and reduces operational costs.

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         

Capital costs can be reduced by up to 50% due to simple trenching at shallow depths, close to surface Flexibility of piping, obstacles (as open channels) can be over- or underpassed reduced installation time Small diameter sewer pipes of HDPE, PVC materials; savings of material costs Aeration of sewage, less development of H2S, with its dangers for workers, inhabitants, as well as corrosion of the pipes may be avoided; No infiltration, less hydraulic load at treatment station and discharge sewers absolutely no leakages (vacuum avoids exfiltration) Sewers may be laid in the same trench with other mains, also with potable water or storm-water, as well as in water protection areas Lower cost to maintain in the long term due to shallow trenching and easy identification of problems In combination of vacuum toilets it creates concentrated waste streams, which makes it feasible to use different waste water treatment techniques, like anaerobic treatment

Limitations 

       

vacuum systems are not capable of transporting sewage over very long distances,( up to 5 km) but can pump long distances from the vacuum station to the next STP or main gravity sewer. vacuum sewerage systems are only capable for the collection of wastewater within a separated system (not for the collection of storm-water) the lines can only reach up to 3–4 km laid in flat area (restrictions of the system due to headlosses (3-4.5 m) (friction and static)) systems should be designed with help of an experienced manufacturer (concepts are usually free of charge) external energy is required at a central point for collecting sewage odours close to the vacuum station can occur, a biofilter may be necessary Integrity of the pipe joints is paramount Mechanical controller requires preventative maintenance for worn parts and seals Vacuum valve can get stuck open and requires a procedure to locate the stuck open valve

Application Fields Vacuum sewer systems becomes more and more the preferred system in the case of particular circumstances: Especially difficult situations as ribbon, peripheral settlements on flat terrain with high specific conduit lengths of longer than 4 metres per inhabitant are predestined for the application of vacuum sewerage systems. In the case of sparse population density the influence of the costs for the collection chambers and vacuum stations are less important in comparison to the costs of long and deep sewers on gravity.

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Missing incline of the ground, unfavourable soil (rocky or swampy grounds) and high groundwater table (with the necessity of dewatering trenches) lead to enormous investment costs in regards to gravity sewerage systems. On the contrary vacuum sewers that are small in diameter can be laid close to the surface in small trenches.

Vacuum sewers can pass through water protection areas and areas with sensitive high ground water tables, because there is no danger of spoiling groundwater resources (vacuum sewers have a high leak tightness due to their material; moreover the vacuum itself does not allow exfiltration). Vacuum systems has also been applied to collect toxic wastewater. Vacuum systems are seen as a priority in many environmentally sensitive areas such as the Couran Cove Eco Resort close to the Barrier Reef in Australia. In seasonal settlements (recreation areas, camping sites etc.) with conventional gravity sewer systems, sedimentation problems can easily occur as automatic spooling from the daily waste water does not take place. High flow velocities within vacuum sewers prevent such sedimentation problems. The Formula 1 race tracks in Shanghai and Abu Dhabi are using a vacuum sewer system for that reason. Even in old narrow and historical villages, the use of vacuum sewer systems becomes more and more important due to a fast (traffic, tourism), costeffective and flexible installation. Good examples and references can be found in France, such as the village of Flavigny, in Oman at the township of Khasab and Al Seeb. Lack of water in many countries and drastic water savings measures have led to difficulties with aging gravity networks with solids blocking in the pipes. Neither the lack of water nor solids affect resp. occur in vacuum sewer systems. That's why this technology becomes interesting for such kind of applications. As PE or PVC pipes are used, no solids from ageing pipes will enter the system. All other solid are kept out at the collection chambers. vacuum sewer systems don't have any manholes to dump big solids into the system.

Collection chambers / vacuum valves Raw sewage flows by gravity from one or more lots into a sealed collection sump. A vacuum interface valve is installed, which is controlled and operated pneumatically without electricity. When a certain amount of sewage has accumulated the controller opens the valve. It is important to understand that the valve shall open only, if the low pressure inside the vacuum sewer line is strong enough to ensure reliable transport; otherwise, an alarm is sent to the control center indicating low vacuum. A minimum value of 0.15 bar for the existing low pressure in the adjacent vacuum line.

When the valve opens, between 20 and 40 l (depending on adjustment and valve) portions of effluent are sucked into the sewer line. Air entering via the incoming gravity line or air vent will be sucked into the sewer line due to the pressure difference to push the sewage. The interface valve will close again after a few seconds. The exact time should have an option to be adjusted and must be long enough to make sure that enough air can enter in order to push the sewage efficiently. This depends on the negative pressure conditions: Generally, the volume of air-stream should be lessened as far as possible, so that the pumps do not have to work unnecessarily. On the other hand minimum ratios of air-to-liquid should be guaranteed to have reliable transporting conditions. Usually the systems work with air-liquid ratios of about 4:1 to 15:1. Vacuum Technology is very reliable and tested

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technology when the right equipment is used. However, due to the numerous collection chambers and vacuum valves throughout the vacuum sewer system and the preventative maintenance needed on these chambers and valves throughout the year, a monitoring system is needed to indicate which locations need inspection and preventative maintenance performed. The restricting minimum diameter of the system should prevent the interface valves and the vacuum sewers from clogging.

So, the connection from the sump to the interface valve should have a diameter of 75mm so that no blockage point is created. Usually, larger particles do not arrive in the sump, even though it still can occur. Large particles can be easily removed from the sump by an operator if required. But generally anything that can fit down a house service line should be able to enter the vacuum system and then the vacuum pump station without blockage.

Vacuum Lines / Description of Hydropneumatic Transport Flow situations in vacuum sewers cannot be simply described with hydraulic laws.

Instead of it a two-phases-flow transport has to be considered (e.g. hydropneumatical). Conveyance takes place by means of a two-phase regime, air (compressible) and effluent. Because of this the continuity equation becomes very complicated.

As it was mentioned before, the main characteristic of vacuum sewerage is the necessity to lay the sewers in the form of a distinct saw-tooth or stepped profile. An effective transport of sewage can only be guaranteed, if the hydraulic losses are agreed to by an approved supplier.

Doses of sewage enter the vacuum line from the collection chambers. As sewage arrive at a low point of the sewer line, sewage is collected there, - until valves upstream open and arriving air will increase the pressure gradient again. Air moving at high velocity into the direction of the vacuum station will exert a strong impulse on the developing sewage.

In this way sewage will be shifted with almost the same velocity over the next peak down the line. The transport of sewage will continue along the sewer line as far as the pressure gradient remains. In a horizontally laid pipe air would stream over water without moving it further.

High flow velocities in the low points of up to 5 m/s avoid any kind of sedimentation, since during the starting movement this kind of flushing effect would take away all hypothetical deposits. Sedimentation problems have never been reported for vacuum sewerage systems.

Prevailing diameters in vacuum sewers are in range of DN 80 and DN 315 (inner diameter). Usually HDPE or PVC pipes are applied in vacuum systems due to their low costs of installation and flexibility. Vacuum sewers have to be absolutely tight.

Therefore, DIN EN 1091 requires a thickness of at least PN 10. Leakages do not appear in vacuum systems due to an absolute tightness of installations (each construction company is easily able to install vacuum pipes).

Vacuum Station The vacuum station consists of rotary vane vacuum pumps (generate vacuum in the sewer lines), a collection tank, and duplicated sewage pumps (duty/standby) that

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discharge sewage away from the collection tanks to a wastewater treatment facility.

The vacuum pumps maintain a negative pressure of between -0.4 and -0.6 bar in the collection tank. When the tank pressure falls under a preset limit, the vacuum pumps will start working to restore the pressure. As such, vacuum pumps run only for a few hours a day and do not need to run continuously.

Collection tanks are mostly made of steel and not of stainless steel due to the risk of local element chemical corrosion. Vacuum tanks are sized according to flow rates and vacuum suction capacity, with typical volumes ranging from 5 to 12 m3. About 75% of the tank’s volume will be required as a vacuum reservoir. With this vacuum reserve, the vacuum pumps are prevented from too high a starting rate, which is normally limited to 10-15 starts per hour (worst case).

Design Planning a vacuum sewerage system seems to be initially a question of design. There is never only one solution at sewer networks in general, but vacuum systems can be designed in many different ways (e.g. connected area, location of the vacuum station, choice of the length profile etc.). A good design needs a perfect overall picture on all the system’s parameters! Some suppliers of vacuum system components help seriously during the design with their assistance. The use of such experienced help is recommendable and preferable.

In the guidelines mentioned above the control of the following parameters is demanded:  

   

air-liquid ratio (depending from distances and population density energetic loss (derived from the maximum trunk length in between the vacuum station and the furthest interface valve as well as from geodetic steps due to topography) network-length (sum of all trunks leading together) flow-rate vacuum reserve volume (considering also the sewer network) maximum tolerable distances in between air inlets (interface valves).

The most significant step in designing a vacuum sewerage system is the choice of a good pipe-routing. System boundaries such as maximum trunk length and additional elevations of the pipe length-profile do not have to be surpassed. As this kind of work requires iterations, design-diagrams have been developed. The maximum trunk length is restricted to 4000 m in absolutely flat terrain. A longer distance can be handled must be done in consultation with a system supplier.

While the norms do not give sufficient information about checking and dimensioning of design parameters, it shall be emphasised, that vacuum sewerage systems could become remarkably larger than the norms show it!

Hints about Operation Unjustified prejudices against “new” technologies still prevail. Highly assumed maintenance/operational costs are the main obstacle against further expansion of vacuum sewerage systems on the market. Problems, especially at collection

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chambers, and frequent system break-downs (drowning) were the birth labour of first vacuum sewerage systems. Nowadays, vacuum systems are reliable when their design is based on special knowledge of professional companies.

A monitoring system is an option to indicate the status of the vacuum valves and collection chambers.

Vacuum stations should be visited at least once a week to carry out a visual inspection. Experiences have shown that a well-designed vacuum station will not need more than one visible control and short check once a week (similar to a pumping system). Operating hours and power consumption of the pumps should be checked regularly. Mechanical and electrical maintenance, cleaning of the vacuum tank, briefly a total check of the vacuum station, should at least be done once a year (oil-change and filter change of the vacuum pumps).

Conclusion Highly estimated operation costs and fear of malfunction have been the main prejudices and obstacles in the past against an expanded use of vacuum sewers.

For an unprejudiced choice of a sewerage concept, it is necessary not to overestimate operational costs of alternative wastewater collection systems.

Further, more difficult conditions during construction have to be considered for conventional gravity sewerage! When a vacuum sewerage system is well designed, operational reliability will be guaranteed.

Vacuum sewerage seems to become more and more important as capital costs could be reduced remarkably. Good references from communities seem to show satisfaction. Especially in cases of sparse population density, flat terrain, and high specific costs of pipe-laying, alternative sewerage systems could become much more economic, also in the long run.

It is significant not to overestimate the operation costs of alternative wastewater collection systems, in comparison with the costs of a conventional gravity system (which constitutes work under more difficult conditions). When a vacuum sewerage system is duly designed and built, its operational reliability is guaranteed.

As engineers and municipal officials become acquainted with the advantages of vacuum sewers, the use of this technology will probably expand more and more worldwide.

It is hoped that the use of alternative sewerage concepts will allow designers and regulators to find ways of keeping project costs at a minimum.

Frequently, a combination of different alternative systems together as well as conventional sections will become the most feasible and the most reliable solution for the collection of wastewater.

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External links References [1] CEN : European Standard DIN EN 1091 “Vacuum Sewerage outside buildings”, (1992) [2] ATV Arbeitsblatt A 116 : “Besondere Entwässerungsverfahren, Unterdruckentwässerung – Druckentwässerung”, Hennef (1992) [3] ATV Arbeitsgruppe 1.1.2 : “Fragen des Betriebs und der Nutzungsdauer von Druck- und Unterdrucksystemen”, Korrespondenz Abwasser (1997), P. 921-922 [4] ATV-Handbuch : “Bau und Betrieb der Kanalisation”, (1995) [5] Ciaponi, C.: Fognature Nere in depressione”, Sistemi di Fognatura, (Centro Studi Deflussi Urbani), Milano (1997) [6] Ciaponi, C.: Un’Esperienza di applicazione del sistema di Fognatura Nera con funzionamento in depressione, Università di Pavia (1986) [7] Garnier, C., Brémond, B. : “Assainissement sous-vide, étude techniqueéconomique”, CEMAGREF, Groupement de Bordeaux, Division Hydraulique Agricole (1986) [8] Ghetti, A.: “Prove Idrauliche e technologiche relative alla fognatura di Venezia”, Padova (1970) [9] Vacusatec vacuum drainage systems

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1.3 Sewage Composition And Characteristics (Qualitative and Quantitative)

1.3.1 Introduction.

1.3.1.1. What is in wastewater?

The liquid waste—wastewater—is essentially the water supply of the community after it has been used in a variety of applications (see Fig. 1–1). From the standpoint of sources of generation, wastewater may be defined as a combination of the liquid or water-carried wastes removed from residences, institutions, and commercial and industrial establishments, together with such groundwater, surface water, and storm water as may be present.

When untreated wastewater accumulates and is allowed to go septic, the decomposition of the organic matter it contains will lead to nuisance conditions including the production of malodorous gases. In addition, untreated wastewater contains numerous pathogenic microorganisms that dwell in the human intestinal tract. Wastewater also contains nutrients, which can stimulate the growth of aquatic plants, and may contain toxic compounds or compounds that potentially may be mutagenic or carcinogenic. For these reasons, the immediate and nuisance-free removal of wastewater from its sources of generation, followed by treatment, reuse, or dispersal into the environment is necessary to protect public health and the environment.

1.3.1.2.What is Wastewater Engineering?

Wastewater engineering is that branch of environmental engineering in which the basic principles of science and engineering are applied to solving the issues associated with the treatment and reuse of wastewater. The ultimate goal of wastewater engineering is the protection of public health in a manner commensurate with environmental, economic, social, and political concerns. To protect public health and the environment, it is necessary to have knowledge of (1) constituents of concern in wastewater, (2) impacts of these constituents when wastewater is dispersed into the environment, (3) the transformation and long-term fate of these constituents in treatment processes, (4) treatment methods that can be used to remove or modify the constituents found in wastewater, and (5) methods for beneficial use or disposal of solids generated by the treatment systems.

To provide an initial perspective on the field of wastewater engineering, common terminology is first defined followed by (1) a discussion of the issues that need to be addressed in the planning and design of wastewater management systems and (2) the current status and new directions in wastewater engineering.

Table 1.3.1 Terminology commonly used in the field of wastewater engineeringa

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1.3.1.3.What means correct operation of the plant by the operators?

All the works and actions needed: (1) for a very good operation of all the plant, according the environmental laws and rules and all the official approvals, edited for the project or concerning the area of

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the impacts by the WWTP. Especially all the outputs (emissions, effluent, biosolids) of the project to comply with the environmental terms approved for the operation of the WWTP (2) for operation of all the systems according the laws and the rules for hygienic and safe working conditions for all personnel in the plant, for the visitors and for all the people in neighboring activities with the project. All the perators must be inoculated against any possible disease according the hygienic regulations and the internalofficial regulation of the WWTP (3) for correct operation all the parts and equipment (piping, tanks, machinery, instruments and all the devices and motors in the plant) to comply with the laws and special rules for similar equipment, according the instructions of the constructor and the special rules, edited and approved form the authorities for the plant.

(4) for all actions in normal , irregular or emergency or conditions, according the instructions and orders by the manager of the plant, responsible for the Operation.

(5) the sampling, samples preparation and transportation to the lab for analysis (6) all the basic tests and analysis, if this is in their responsibilities (7) calendar keeping for all the daily works, all the events and all the actions in any programmed work or any event and the results and observations from any action (8) weekly, monthly or bimonthly, semi-annual or annual reports with all the results and full report for the situation of the equipment.

1.3.1.4. What means correct maintenance?

All the actions and works needed for: (1) all the parts and the equipment (piping, tanks, buildings, networks machinery, instruments and all the devices and motors in the plant) to comply with the laws and with all the manual and limitations defined by the constructors of every part and kind of equipment and instruments.

(2) All preventive maintenance programs must be followed (3)All repairing actions and maintenance of all equipment (4) for maintenance of all systems according the laws and the rules for hygienic and safe working conditions in the working areas. All the technicians must be innoculated against any possible disease according the hygienic regulations and the internal-official regulation of the WWTP

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(5) keeping calendar for all the daily maintenance works, all the events and all the actions in any programmed work or any event and the results and observations from any action (6) contribution to monthly or bimonthly, semi-annual or annual reports with all the damages, events, way of repair or action and full report for the situation of the equipment.

1.3.1.5.What the operator must know?

The operators must know all the basic and main information, theory and instructions for operation and maintenance : (1) all the basic aspects to understand and realize all the main processes (2) all the basic theory and practice to operate and maintain correctly the WWTP (3) all the information needed for safety and healthy conditions in the working areas at the WWTPs 1.3.1.6. What makes wastewater dangerous?

A large Number of microorganisms are listed in the following tables, most related with pathogenic diseases for people and animals:

TABLE 1.3.2 Types And Number Of Microorganisms Typically Found In Untreated Domestic Wastewater

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Which diseases can be spread from wastewater systems?

TABLE 1.3.3. INFECTIOUS AGENTS POTENTIALLY PRESENT IN RAW DOMESTIC WASTEWATER

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From: Environmental Engineers Handbook p.20,table 7.1.13 1.3.2. Components Of Wastewater Flows The components that make up the wastewater flow from a community depend on the type of collection system used and may include: 1. Domestic (also called sanitary) wastewater. Wastewater discharged from residences and from commercial, institutional, and similar facilities.

2. Industrial wastewater. Wastewater in which industrial wastes predominate.

3. Infiltration/inflow. Water that enters the collection system through indirect

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and direct means. Infiltration is extraneous water that enters the collection system through leaking joints, cracks and breaks, or porous walls. Inflow is stormwater that enters the collection system from storm drain connections (catch basins), roof leaders, foundation and basement drains, or through access port (manhole) covers.

4. Stormwater. Runoff resulting from rainfall and snowmelt.

Three types of collection systems are used for the removal of wastewater and stormwater: sanitary collection systems, storm collection systems, and combined collection systems. Where separate collection systems are used for the collection of wastewater (sanitary collection systems) and stormwater (storm collection systems), wastewater flows in sanitary collection systems consist of three major components: (1) domestic wastewater, (2) industrial wastewater, and (3) infiltration/inflow. Where only one collection system (combined) is used, wastewater flows consist of these three components plus stormwater. In both cases, the percentage of the wastewater components will vary with local conditions and the time of the year.

1.3.3. Wastewater Sources And Flowrates Data that can be used to estimate average wastewater flowrates from various domestic, commercial, institutional, and industrial sources and the infiltration/inflow contribare presented in this section. Variations in the flowrates that must be established before collection systems and treatment facilities are designed are also discussed.

1.3.3.1.Domestic Wastewater Sources and Flowrates The principal sources of domestic wastewater in a community are the residential areas and commercial districts. Other important sources include institutional and recreational

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facilities. For areas now served with collection systems, wastewater flowrates are commonly determined from existing records or by direct field measurements (see Fig. ‌).

For new developments, wastewater flowrates are derived from an analysis of population data and estimates of per capita wastewater flowrates from similar communities.

Water consumption records may also be used for estimating flowrates. These records are especially useful in other parts of the world where water use for landscape irrigation is limited and 90 percent or more of the water used becomes wastewater.

In the United States, on the average about 60 to 90 percent of the per capita water consumption becomes wastewater. In Greece and other Meditteranean areas, 7590% of the consumption becomes wastewater (with variations depending on seasons and areas with different main activities).

The higher percentages apply to the northern areas during cold weather; the lower percentages are applicable to the semiarid region of the southwestern United States where landscape irrigation is used extensively.

When water consumption records are used for estimating wastewater flowrates, the amount of water consumed for purposes such as landscape irrigation (that is not discharged to the collection system), leakage from water mains and service pipes, or product water that is used by manufacturing establishments must be evaluated carefully.

Residential Areas. For many residential areas, wastewater flowrates are commonly determined on population and the average per capita contribution of wastewater.

For residential areas where large residential development is planned, it is often advisable to develop flowrates on the basis of land-use areas and anticipated population densities.

Where possible, these rates should be based on actual flow data from selected similar communities, preferably in the same locale. In the past, the preparation of opulation projections for use in estimating wastewater flowrates was often the

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responsibility of the engineer, but today population projection data are usually available from local, regional, and state planning agencies.

Wastewater flowrates can vary depending on the quantity and quality of the water supply; rate structure; and economic, social, and other characteristics of the community.

Data on ranges and typical flow rate values are given in Table 3–1 for residential sources in the United States. Beginning in recent years, greater attention is now being given to water conservation and the installation of water-conserving devices and appliances.

Reduced household water use changes not only the quantity of wastewater generated but, as discussed later in this chapter, the characteristics of wastewater as well.

Main components of the municipal wastewater in U.S.A. and in European Areas Table 1.3.4 Typical Composition Of Untreated Domestic Wastewater

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1.3.3.2.Commercial Districts. Depending on the function and activity, unit flowrates for commercial facilities can vary widely. Because of the wide variations that have been observed, every effort should be made to obtain records from actual or similar facilities.

If no other records are available, estimates for selected commercial sources, based on function or persons served, may be made using the data presented in Table 3–2.

In the past, commercial wastewater flowrates were often based on existing or anticipated future development or comparative data. Flowrates were generally expressed in terms of quantity of flow per unit area [i.e., m3/ha_d (gal/ac_d)].

Typical unit-flowrate allowances for commercial developments normally range from 7.5 to 14 m/ha_d (800 to 1500 gal/ac_d). The later approach can be used to check the values obtained from existing records or estimates made using Table 3–2.

Typical wastewater flowrates from commercial sources in the United States

Table 1.3.5.

Typical wastewater flowrates from commercial sources in the United States and in Europe Flowrate, L/unit.d in USA (*)

Flowrate, L/unit.d In south Europe

Source

Unit

Range

Typical

Range

Typical

Airport

Passenger

11-19

15

10-20

15

Apartment

Bedroom

380-570

450

150-230

190

200-500

300

Employee

30-57

40

30-50

40

Vehicle served

30-57

40

30-60

40

Seat-

45-95

80

30-50

40

Employee

30-57

40

30-50

40

Person

40-60

50

40-60

50

Hotel

Automobile service station Bar/cocktail lounge

Conference center

Guest

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Department store

Toilet room

13002300

1500

1000-2000

1500

Employee

30-57

40

30-50

40

Industrial Employee building (sanitary wastes only)

57-130

75

50-100

75

Motel (with kitchen)

Guest

210-340

230

200-300

230

Motel (without kitchen)

Guest

190-290

210

150-250

200

Office

Employee

25-60

50

30-60

50

Public lavatory

User

11-19

15

10-20

15

Restaurant:

Customer

26-40

35

20-60

40

Shopping center

Employee

26-50

40

30-50

40

Parking space/

4-11

8

4-11

8

Theater-Cinema Seat/play (Indoor)

8-15

10

8-15

10

Assembly hall

Guest

11-19

15

10-20

15

Hospital

Bed

660-1500

1000

400-800

600

20-60

40

Bed

280-470

380

200-400

300

Student

60-120

100

60-120

100

Student

40-80

60

40-80

60

Employee Institutions other than hospitals School, day With cafeteria, gym, and showers With cafeteria only

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School, Student 280-380 320 280-380 boarding (*) Adapted from Metcalf & Eddy (1991), Salvato (1992), and Crites and Tchobanoglous (1998).

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Fig. 1.3.1.Typical pattern of hourly variations in domestic wastewater flow rates.

(Reprinted from Metcalf and Eddy, Inc., 1991.)

1.3.4. Flow Variations Flow rate information needed in designing a wastewater treatment plant includes (Metcalf and Eddy, Inc. 1991): AVERAGE DAILY FLOW—The average flow rate occurring over a 24-hr period based on total annual flow rate data. Environmental engineers use average flow rate in evaluating treatment plant capacity and in developing flow rate ratios.

MAXIMUM DAILY FLOW—The maximum flow rate occurring over a 24-hr period based on annual operating data. The maximum daily flowrate is important in the design of facilities involving retention time, such as equalization basins and chlorine-contact tanks.

PEAK HOURLY FLOW—The peak sustained hourly flow rate occurring during a 24hr period based on annual operating data. Data on peak hourly flows are needed for the design of collection and interceptor sewers, wastewater pumping stations, wastewater flowmeters, grit chambers, sedimentation tanks, chlorine-contact tanks, and conduits or channels in the treatment plant.

MINIMUM DAILY FLOW—The minimum flow rate that occurs over a 24-hr period based on annual operating data. Minimum flow rates are important in sizing conduits where solids deposition might occur at low flow rates.

MINIMUM HOURLY FLOW—The minimum sustained hourly flow rate occurring over a 24-hr period based on annual operating data. Environmental engineers need data and weekly wastewater flow rates, respectively (Metcalf and Eddy, Inc. 1991).

Wide variations of wastewater flow rates can occur within a municipality. For example, minimum to maximum flow rates range from 20 to 400% of the average daily rate for small communities with less than 1000 people, from 50 to 300% for communities with populations between 1000 and 10,000, and up to 200% for communities up to 100,000 in population. Large municipalities have variations from 1.25 to 1.5 average flow. When storm water runoff goes into municipal sewerage systems, the maximum flow rate is often two to four times the average dry-weather flow.

(Water Pollution Control Federation and American Society of Civil Engineers 1977).

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Fig. 1.3.2.Typical patterns of daily and weekly variations in domestic wastewater flow rates. (Reprinted from Metcalf and Eddy, Inc., 1991.)

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Main constituents and parameters for characterizing the quality of the wastewater : 1) Solids suspended- solids solved, volatile and non-volatile solids, organic-inorganicbiodegradable solids, 2) Grit, Fat-Grease, gases, 3) odors, 4) BOD5, COD, TKN, TP, pH, Alkalinity, 5) Microbes and threats for the health 6) Terminology, meaning of terms used in environmental protection and in the treatment processes Table 1.3.6. Principal constituents of concern in wastewater treatment (with their importance in wastewater management) —————————————————————————————————————— —————————— Constituent

Reason for importance

—————————————————————————————————————— —————————— Suspended solids

Suspended solids can lead to the development of sludge deposits and anaerobic conditions when untreated wastewater is discharged in the aquatic environment.

Biodegradable organics

Composed principally of proteins, carbohydrates, and fats, biodegradable organics are measured most commonly in terms of BOD (biochemical oxygen demand) and COD (chemical oxygen demand). If discharged untreated to the environment, their biological stabilization can lead to the depletion of natural oxygen resources and to the development of septic conditions.

Pathogens

Communicable diseases can be transmitted by the pathogenic organisms that may be present in wastewater.

Nutrients

Both nitrogen and phosphorus, along with carbon, are essential nutrients for growth. When discharged to the aquatic environment, these nutrients can lead to the growth of undesirable aquatic life. When discharged in excessive amounts on land, they can also lead to the pollution of groundwater.

Priority pollutants

Organic and inorganic compounds selected on the basis of their known or suspected carcinogenicity, mutagenicity, teratogenicity, or high acute toxicity. Many of these compounds are found in wastewater.

Refractory organics

These organics tend to resist conventional methods of

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Heavy metals

Heavy metals are usually added to wastewater from commercial and industrial activities and may have to be removed if the wastewater is to be reused.

Dissolved inorganics

Inorganic constituents such as calcium, sodium, and sulfate are added to the original domestic water supply as a result of water use and may have to be removed if the wastewater is to be reused.

—————————————————————————————————————— —————————— Adapted, in part, from Crites and Tchobanoglous (1998) (Reprinted from Metcalf and Eddy, Inc., 1991.)

Figure 1.3.3.

Samplers used to collect wastewater samples for analysis: (a) refrigerated unit used to collect daily composite amples and (b) portable sampler used to collect individual hourly samples throughout a day at different locations. The individual samples are composited to obtain flow-weighted mass loadings.

(WasteWater Engineering, Treatment and Reuse, Metcalf & Eddy, USA 2003)

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Table 1.3.7. Common analyses used to assess the constituents found in wastewater a Abbreviation/ Testb

definition

Use or significance of test results

Physical characteristics Total solids

TS

Total volatile solids

TVS

Total fixed solids

TFS

Total suspended solids TSS Volatile suspended VSS solids Fixed suspended solids FSS Total dissolved solids Volatile dissolved solids Total fixed dissolved

To assess the reuse potential of a wastewater and to determine the most suitable type of operations and processes for its treatment

TDS (TS - TSS) VDS FDS

solids Settleable solids

To determine those solids that will settle by gravity in a specified time period

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Particle size distribution

PSD

To asses the performance of treatment processes

Turbidity

NTU

Used to asses the quality of treated wastewater

Color

Light brown, grey, black

To assess the condition of wastewater (fresh or septic)

Transmittance

%T

Used to assess the suitability of treated effluent for UV disinfection

Odor

TON

To determine if odors will be a problem

Temperature

°C or °F

Important in the design and operation of biological processes in treatment facilities

Density



Conductivity

EC

Used to assess the suitability of treated effluent for agricultural applications

Inorganic chemical characteristics NH4+ Free ammonia Organic nitrogen

Org N

Total Kjeldahl nitrogen TKN (Org N + NH4+)

Used as a measure of the nutrients present and the degree of decomposition in the wastewater;

Nitrites

NO2-

the oxidized forms can be taken as a measure

Nitrates

NO3-

of the degree of oxidation. Used as a measure

Total nitrogen

TN

Inorganic phosphorus

Inorg P

Total phosphorus

TP

Organic phosphorus

Org P

of the nutrients present

Continued on following page

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Table 1.3.7. (Continued from previous page) Abbreviation/ Testb

definition

Use or significance of test results

pH

pH = - log [H+]

A measure of the acidity or basicity of an aqueous solution

Alkalinity

ďƒĽ HCO3- + CO3- 2 + OH-

A measure of the buffering capacity of the wastewater

- H+ Chloride

Cl-

To assess the suitability of wastewater for agricultural reuse

Sulfate

SO4-2

To assess the potential for the formation of odors and may impact the treatability of the waste sludge

Metals

As, Cd, Ca, Cr, Co, Cu, Pb, Mg, Hg, Mo, Ni, Se, Na, Zn

To assess the suitability of the wastewater for reuse and for toxicity effects in treatment. Trace amounts of metals are important in biological treatment

Specific inorganic elements and compounds Various gases

To assess presence or absence of a specific constituent

O2, CO2, NH3, H2S, CH4

The presence or absence of specific gases

Organic chemical characteristics Five-day carbonaceous CBOD5 biochemical oxygen demand

A measure of the amount of oxygen required to stabilize a waste biologically (*)

Ultimate carbonaceous biochemical oxygen demand

A measure of the amount of oxygen required to stabilize a waste biologically

UBOD (also BODu, BODL)

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Nitrogenous oxygen demand

NOD

A measure of the amount of oxygen required to oxidize biologically the nitrogen in the wastewater to nitrate

Chemical oxygen

COD

Often used as a substitute for the BOD test

Total organic carbon

TOC

Often used as a substitute for the BOD test

Specific organic

MBAS, CTAS

To determine presence of specific organic compounds and to assess whether special design measures will be needed for removal

MPN (most probable number)

To asses presence of pathogenic bacteria and effectiveness of disinfection process

Bacteria, protozoa helminths, viruses

To asses presence of specific organisms in connection with plant operation and for reuse

TUa and TUc

Toxic unit acute, Toxic unit chronic

demand

compounds and classes of compounds Biological characteristics Coliform organisms

Specific microorganisms

Toxicity

————————————————————————————————————————— ——————————— a Adapted, in part, from Crites and Tchobanoglous (1998) b Details on the various tests may be found in Standard Methods (1998)

(*) Biochemical Oxygen Demand Measurement In the natural water system, most organic contaminants are degraded by bacterial metabolism. The amount of oxygen used in the metabolism of biodegradable organics is termed Biochemical Oxygen Demand (BOD). Therefore, BOD is a common indicator of the degree of contamination of natural water by organic pollutants.

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Table 1.3.8. Types And Number Of Microorganisms Typically Found In Untreated Domestic Wastewater (Communicable diseases can be transmitted by the following pathogenic organisms, that may be present in wastewater).

In the following table are listed Odorous compounds in untreated sewage, related with nuisance in the neighboring areas .

Table 1.3.9 Odorous Compounds Associated With Untreated Wastewater

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1.3.5. More Analytical Approach To The Main Parameters: pH... pH is a measure of how acidic or alkaline a solution is. In pure water at room temperature, a small fraction (about two out of every billion) of the water molecules (H2O, or really, H-O-H) splits, or dissociates, spontaneously, into one positively charged hydrogen ion (H+) and one negatively charged hydroxide ion (OH-) each.

There is an equal number of each ion, so the water is said to be "neutral". Some materials, when dissolved in water, will produce an excess of (H+), either because they contain these ions and release them when they dissolve, or because they react with the water and cause it to produce the extra hydrogen ions. Substances which do this are called acids. Likewise, some chemicals, called bases or alkalis, produce an excess of hydroxide ions. The scale which is used to describe the concentration of acid or base is known as pH, for power or potential of the Hydrogen ion. A pH of 7 is neutral. pH's above 7 are alkaline (basic); below 7, acidic. The scale runs from about zero, which is very acidic, to fourteen, which is highly alkaline. The scale is logarithmic, meaning that each change of one unit of pH represents a factor of 10 change in concentration of hydrogen ion. So a solution which has a pH of 3 contains 10 times as many (H+) ions as the same volume of a solution with a pH of 4, 100 times as many as one with a pH of 5, a thousand times as many as one of pH 6, and so on. Some common materials and their approximate pH's are ; acids : carbonated beverages, 2 to 4; lemon juice, about 2.3; vinegar, about 3 and bases : baking soda, 8.4; milk of magnesia 10.5; ammonia, 11.7; lye, 14 to 15.

While the pH measures the concentration of hydrogen or hydroxide ions, it may not measure the total amount of acid or base in the solution. This is because most acids and bases do not dissociate completely in water. That is, they only release a portion of their hydrogen or hydroxide ions. A strong acid, like hydrochloric acid, HCl, releases essentially all of its H+ in water. The concentration of H+ is the same as the total concentration of the acid. A weak acid, like acetic acid (the acid in vinegar), may release only a few percent of the hydrogen that it has available. If you are trying to neutralize an acid by adding a base, like sodium hydroxide, the amount you would need to neutralize a strong acid could be calculated directly from the pH of the acid solution. But for a weak acid, the pH does not tell the whole story; the total amount of base needed would be a lot more. This is because as the OH - from the base reacts with the H+ in solution to form water, more H+ will break loose from the undissociated portion of the acid to take its place. The neutralization will not be complete until all of the weak acid has dissociated.

More…

MORE INFORMATION ABOUT pH ……………… pH... pH is one of the most commonly made measurements in water testing, but one of the least understood. Here is an attempt at an explanation: In order to understand

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the pH scale, we have to discuss the ideas of moles and of logarithms.

Moles : When chemists talk about the amount of a substance, they often like to use the unit of moles, rather than grams. A mole of a substance is, simply, the number of grams of that substance equal to its molecular weight. A mole of water, weighs about 18 grams, because water has a molecular weight of about 18. A mole of calcium carbonate, CaCO3, weighs about 100 grams; a mole of methyl alcohol, CH3OH, 32 grams, etc. The advantage for chemists of using moles is that an equal number of moles of any substance contains the same number of molecules, so it is easier to calculate the amounts of substances which react with one another.

In a liter of pure water at room temperature the number of moles of hydrogen ions is about 0.0000001. (For hydrogen, with an atomic weight of 1, this is also about equal to the number of grams of hydrogen ions.) In scientific notation, this is written as 1 x 10-7, where the superscript,-7, is known as a power, an exponent, or a logarithm. (All three terms mean the same thing. The seven indicates the number of places to the right of the decimal point that the "one" is located.) It turns out, when measuring hydrogen ion concentration electrochemically, that the electrical potential (voltage) generated at the measuring electrode is directly related not to the H+ concentration, but to the logarithm of the H+ concentration. This makes it more convenient to refer to the H+ concentration in terms of its logarithm. And since H+ concentrations in water solutions are almost always less than one mole per liter, the exponent is almost always going to be negative, because that is the way scientific notation expresses numbers less than one. So, the negative of the logarithm of the hydrogen ion concentration in a solution is given a special name. It is called the pH, which stands for the potential of the hydrogen ion.

Of course, in the pure water, the concentration of hydroxide ions is also 1 x 10 -7 moles per liter, since each water molecule that dissociates produces one ion of each type. The water is said to be neutral. It has a pH of 7 and also a pOH of 7, where the term pOH refers to the negative logarithm of the hydroxide ion concentration. There are substances which, when dissolved in water, will upset that balance, and produce an excess of either H+ or OH-. They may contain those ions and release them (dissociate) when they dissolve, or they may react with the water (hydrolyze) and produce them that way. Those substances which increase the concentration of H+ are called acids; those which decrease it (and increase the OH- ) are bases or alkalis.

For instance, if a strong acid solution increases the H + concentration to 0.1 moles per liter (1 x 10-1), which has a million times as many H+ ions as a neutral solution, then the pH is equal to 1. Similarly, if a strong base solution contains 0.1 moles per liter of OH- ions, it has a pOH of 1. According to the laws of chemical equilibrium, the pH and the pOH always add up to 14 (at about room temperature), so the solution with the pOH of 1 has a pH of 13. Most solutions have a pH between 0 and 14, and 7 is the neutral point. pH's below 7 are increasingly acidic as the number decreases; pH's above 7 are increasingly alkaline. And since the scale is logarithmic, each unit change in pH represents 10 times as many ions in solution.

A strong acid or base is one which dissociates completely when it dissolves in water.

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The amount of it in solution can be estimated from the pH. Most acids and bases, however, are weak; they dissociate or hydrolyze only partially. Many solutions also contain mixtures of several acidic or basic substances. In these cases, it is difficult to estimate the total amount of acid or base by measuring the pH, so this must be done by titration. As every high school chemistry student knows, acids react with bases to form water and salts. Therefore, an acid is titrated using a standard base, and visa versa. In water and wastewater analysis, the amount of acid needed to titrate a solution to a particular pH is a measure of the acid neutralizing capacity of that solution, and is referred to as the solution's alkalinity. In natural waters, the pH is most often controlled by the concentrations of carbonate, bicarbonate, and carbon dioxide, since these are products of respiration and fermentation. Because of this, alkalinity is usually measured in terms of the amount of acid needed to reach the pH of a pure solution of one or another of these substances. Similarly, acidity is defined as base neutralizing capacity, and is measured by titration against a standard base.

While a chemist might prefer to measure these quantities in moles per liter, engineers seem more comfortable with standard weight units. So acidity and alkalinity are usually expressed in units of milligrams per liter of calcium carbonate.

Calcium carbonate, or limestone, is a weakly alkaline material, 50 grams of which react with one mole of hydrogen ions.

Titrations and Buffer Solutions...

A solution of an pure acid will have a pH determined by its concentration and by how strong an acid it is - that is, how easily it releases a proton (hydrogen ion) when dissolved in water. As we titrate a solution of an acid with strong base, hydrogen ions are consumed by reacting with the added hydroxide ions to form water, which leads to an increase in the pH of the solution. For an acid with one proton which can dissociate ("monoprotic" acid), the titration will be complete when the number of moles of hydroxide added equals the number of moles of acid originally present. If we call the fraction of acid which has been neutralized f, then the titration is complete when f = 1. (For an acid with two replaceable hydrogens ("diprotic" acid), the titration is complete at f = 2, and so forth.) If more base is added after the acid is all neutralized, then the pH of the solution will be determined by the concentration of hydroxide - essentially as if it were being added to plain water. The initial, final, and intermediate pH's will be a function of the acid's concentration, strength, and the value of f. The calculations are different for strong and weak acids, so let's consider them separately.

For a strong acid, essentially all of the acid dissociates, so that the concentration of hydrogen ions (H+) is equal to the concentration of the acid. Therefore, the initial pH of the acid solution is equal to the negative logarithm of the concentration of the acid in moles per liter (by the definition of pH). When 90 % of the acid has been neutralized (f = 0.9), the concentration of H+ is only one-tenth of its what it was originally - so the pH will be one unit higher, since -log(0.1) = 1. When 99 % has been neutralized (f = 0.99), the pH is 2 units higher, and so on. When f = 1, the pH should equal 7 - and any further addition will raise the pH to a value equal to [14 minus pOH], just as though it were being added to pure water. (Note that we have made

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the simplifying assumption here of ignoring the increase in the volume of the solution due to adding the base - but this could easily be accounted for. We also assumed that the original acid concentration was a lot higher than 10 -7 molar, so that we could ignore the H+ contributed by the dissociation of water.)

For a weak acid, an approximate formula can be derived for the pH of a solution of the pure acid which states that ; pH = 1/2 ( pKa + pC ) The pKa is the negative logarithm of the "acid dissociation constant", and pC is the negative logarithm of the concentration of the acid in moles per liter. (The pKa is a property of each particular acid, and is a number which can be looked up in reference books.) So, for example, a 0.1 molar solution (pC = 1) of an acid which has a pKa of 5, would have a pH of about 1/2(5+1), or 3.

For the hypothetical acid with the formula, HA, the reaction which occurs as the titration with strong base proceeds can be written as ; HA + OH- ---> A- + H2O The major chemical species in the solution are the remaining acid, HA, which has not been neutralized, and the anion (negative ion), A-, which is called the "conjugate base." It is the ratio of these which determines the pH, according to the formula ; pH = pKa + log [ ( A-) / ( HA ) ] where ; (A-) means the molar concentration of A- and (HA) is the molar concentration of the remaining HA. Note that this formula can also be expressed as ; pH = pKa + log [ f / ( 1 - f ) ] When the concentration of the two species is equal, the ratio [ ( A- ) / ( HA ) ] equals 1 - and since the logarithm of 1 equals zero, the pH is equal to the pKa. At an earlier point in the titration, when, say, one-tenth of of the acid had been neutralized, the pH would be equal to pKa + log ( 0.1 / 0.9 ). This works out to about 0.95 pH units below the pKa. When 90% of the titration is complete, the pH should be about equal to pKa + log ( 0.9 / 0.1 ), or about 0.95 units above the pK a. So the pH change during the middle 80% of the titration will vary less than one unit below or above the value of the pKa. Likewise, you can easily show that between the 1% and 99% points of the titration, the pH will vary between 2 units below and two units above the pK a. (Note that the same assumptions are made as for the strong acid case discussed above.)

For a monoprotic acid (also called a "monobasic" acid - how's that for a confusing term) at the end of the titration (f = 1), there is another approximate formula for the pH ;

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pH = 7 + 1/2 ( pKa - pC ) For the previous example of a 0.1 molar solution (pC = 1) of an acid which has a pK a of 5, the endpoint pH would be about 7 + 1/2 ( 5 - 1 ), or 9.

"Diprotic" (also called "dibasic") acids can be thought of of dissociating in two steps.

For a generic dibasic acid H2Z, loss of one proton can be written as ; H2Z <---> H+ + HZfor which pKa is called pK1 and loss of the second proton is written as ; HZ- <---> H+ + Z= for which pKa is called pK2. Since HZ- is negatively charged, and positive charges are attracted to negative charges, it is harder for the second proton to break away.

Because of this, the value of pK2 is usually several units higher than pK1. Often, a solution of a dibasic acid behaves essentially like a mixture of two independent acids, one being a much weaker acid than the other. The titration curve runs from f = 0 to f = 2, and looks like one monobasic titration curve followed by another one at a higher pK. The pH's at f = 0.5 and f = 1.5 correspond to the values of pK1 and pK2, respectively. If the acid is concentrated enough that the contribution due to the dissociation of water can be ignored, the pH at f = 1 is about equal to the average of pK1 and pK2. (In cases where the pK's are fairly close the simple model does not work so well).

The pH range near the pKa value of a particular weak acid is sometimes referred to as the buffer region. As we have seen, the pH does not change much in this region when strong acid or base is added-- even in amounts which are a significant fraction of the amount of the weak acid/base mixture itself. This property is made use of in chemical, biological and pharmaceutical work - and in nature - to keep solutions at a near-constant pH. To make a buffer solution, you do not actually need to titrate a weak acid or base. For instance, to make an acetic acid/acetate buffer you can purchase acetic acid and the salt, sodium acetate, from a chemical supplier and make a solution containing the proportions which will give the desired pH, based on the eq. given above. The buffer would be most efficient at a pH near the acid's pK a value of 4.7.

In natural waters and in wastewater treatment plants, the water most often relies on the carbonic acid/bicarbonate system for buffering near neutral pH (pK = 6.3). The carbonic acid is formed when carbon dioxide dissolves in water. It is a product of aerobic or anaerobic respiration by microorganisms living in the water, and is also present in air; carbonates are present is some minerals, such as limestone, with which the water may come in contact.

In laboratories, phosphate buffers are often used in chemistry or bacteriology to keep pH conditions constant. Phosphoric acid is a tribasic acid, with pK's of 2.1, 7.2,

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and about 12.0. You can see that the middle one, corresponding to a mixture of the ions H2PO4- and HPO4=, would be very useful for making neutral buffers. In wastewater analysis, phosphate buffers are used in the BOD test, the DPD method for total chlorine residual and the colorimetric test for cyanide, for diluting and rinsing in coliform bacterial testing, and for calibrating pH meters.

As an example of the protective effect of buffer solutions, consider the 0.01 M (moles per liter) carbonic acid/bicarbonate/carbonate system shown in the last of the six titration curves. If we take the case of this system at a pH of 7.0, the graph shows that the value of f equals about 0.83. This means that of the total concentration of 0.01 moles per liter, 83% (0.0083 moles per liter) is in the form of bicarbonate (HCO3-) - so that 17% (0.0017 moles per liter) is in the form of carbonic acid (H2CO3). The ratio, 0.0083 / 0.0017, equals 4.88 - the logarithm of which is 0.69, or about 0.7. Add this to the pK1 of 6.3, according to the formula above, and you get a pH of 7.0. Now, let's say we add 0.001 moles of a strong acid to a liter of this solution. (Remember that adding this amount of strong acid to pure water will lower the pH from 7 down to a value of 3). The reaction which would occur ; HCO3- + H+ ---> H2CO3 Dissolved Oxygen ( DO )...

Like solids and liquids, gases can dissolve in water. And, like solids and liquids, different gases vary greatly in their solubilities, i.e, how much can dissolve in water.

A solution containing the maximum concentration that the water can hold is said to be saturated. Oxygen gas, the element which exists in the form of O2 molecules, is not very water soluble. A saturated solution at room temperature and normal pressure contains only about 9 parts per million of DO by weight (9 mg / L). Lower temperatures or higher pressures increase the solubility, and visa versa.

Significance...

Dissolved oxygen is essential for fish to breathe. Many microbial forms require it, as well. The oxygen bound in the water molecule (H2O) is not available for this purpose, and is in the wrong "oxidation state", anyway. The low solubility of oxygen in water means that it does not take much oxygen-consuming material to deplete the DO. As mentioned before, the biodegradation products of bacteria which do not require oxygen are foul-smelling, toxic, and/or flammable. Sufficient DO is essential for the proper operation of many wastewater treatment processes. Activated sludge tanks often have their DO monitored continuously. Low DO's may be set to trigger an alarm or activate a control loop which will increase the supply of air to the tank.

Measurement...

DO can be measured by a fairly tricky wet chemical procedure known as the Winkler titration. The DO is first trapped, or "fixed", as an orange-colored oxide of manganese. This is then dissolved with sulfuric acid in the presence of iodide ion,

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which is converted to iodine by the oxidized manganese. The iodine is titrated using standard sodium thiosulfate. The original dissolved oxygen concentration is calculated from the volume of thiosulfate solution needed. Measurements of DO can be made more conveniently with electrochemical instrumentation. "DO - meters" are subject to fewer interferences than the Winkler titration. They are portable and can be calibrated directly by using the oxygen in the air. Δεν είν αι δυν ατή η προβολ ή αυτής της εικόν ας αυτή τη στιγ μή.

Δεν είν αι δυν ατή η προβολ ή αυτής της εικόν ας αυτή τη στιγ μή.

Biochemical Oxygen Demand...

General...

Biochemical Oxygen Demand is a common, environmental procedure for determining the extent to which oxygen within a sample can support microbial life.

The following tutorial explores the theory and basics of performing this test when one has little or no prior experience. This method is popular in many environmental laboratories analyzing waste water, compost, sludge, and soil samples. Although methods for each matrix are similar, this tutorial focuses on the method associated with only waste water effluents. The main details of this method are taken specifically from Standard Methods for the Examination of Water and Wastewater (Method 507: 1985, and Method 218B: 1971) and the US Environmental Protection Agency of 1979 (Method 405.1). Slight variations and additional insight are added from my experience as an analyst, and modifications will be noted. Other methods may exist amongst laboratories performing this test, so it must be stressed that this method, although approved, is not all inclusive. In addition, this procedure is only suitable for samples void of serious matrix interferences. To gain a broader appreciation of oxygen demand, additional avenues of interest may be explored including CBOD (carbonaceous oxygen demand), COD (chemical oxygen demand), and TOC (total organic carbon).

The test for Biochemical Oxygen Demand is especially important in waste water treatment, food manufacturing, and filtration facilities where the concentration of oxygen is crucial to the overall process and end products. High concentrations of dissolved oxygen (DO) predict that oxygen uptake by microorganisms is low along with the required break down of nutrient sources in the medium (sample). On the other hand, low DO readings signify high oxygen demand from microorganisms, and can lead to possible sources of contamination depending on the process.

Performing the test for BOD requires a significant time commitment for preparation and analysis. The entire process requires five days, and it is not until the last day where data is collected and evaluated. During this time, samples are initially seeded with microorganisms and supplied with a carbon nutrient source of glucose-glutamic acid. The sample is then introduced to an environment suitable for bacterial growth at reproducible temperatures, nutrient sources, and light within a 20oC incubator such that oxygen will be consumed. Quality controls, standards and dilutions are also

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run to test for accuracy and precision. Determination of the dissolved oxygen within the sample can be determined through Winkler titration methods. The difference in initial DO readings (prior to incubation) and final DO readings (after 5 days of incubation) predicts the BOD of the sample. A suitable detection limit as per environmental QC is 1 mg / L. Why 5 Days ?...

It can take as long as 25 days before no further changes can be detected in a bottle in which a BOD test is being conducted. Depending on the nature of the sample, the test may be near completion in a few days. A reasonable compromise between waiting too long to get results and getting unreliable answers is 5 days. As long as the samples are pretty much the same from one sampling period to another, the 5day test works fairly well. For example, samples from a process in a waste treatment plant will have essentially the same nature over long periods. The 5-day BOD will be highly meaningful in showing variations in plant performance. The following figure shows simulation of the BOD test with different rate coefficients. Note the vertical line for 5 days. If the samples are quite different in their composition, the error in comparing them at 5 days will be great, and a longer time for the test would be better. This must be balanced by a long wait before having results, and delay in making adjustments based on these results may be costly Fig. 1.3.4 Typical BOD curve for domestic wastewater showing carbonaceous and nitrogenous oxygen demands. (Reprinted, with permission, from S.R. Qasim, 1985, Wastewater treatment plants-Planning, design, and operation, New York: Holt, Rinehart and Winston.)

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MORE INFORMATION ABOUT BOD MEASUREMENT ………………

Required Equipment...

The following is a list of necessary materials and equipment for starting the procedure : (1) Series of 250-300 ml BOD bottles with ground glass stoppers, and caps, (2) Incubator set at 20oC, (3) Two large carboys (20 liter capacity depending on sample amount), (4) Series of class A pipets (0.2 mL - 10 mL), (5) Aeration device, (6) pH - meter, (7) Six 500 ml ehrlenmeyer flasks, (8) Millipore water, (9) Phosphate buffer pillows for every 6 liter carboy volume, (10) DO - meter with membrane electrode, (11) Seed, (12) 50 ml class A buret, (13) Stir plates and stir bars, (14) Series of volumetric flasks, (15) Series of beakers and (16) Deionized water.

Required Reagents...

The following is a list of reagents used in this method that are commercially prepared : (1) Concentrated sulfuric acid, (2) 0.0375 N Sodium thiosulfate, (3) Starch indicator, (4) Crystalline D-glucose and glutamic acid, (5) Bleach (5.25 %), (6) Acetic acid, (7) Potassium iodide, (8) Sodium hydroxide pellets, (9) Manganese sulfate and (10) Sodium sulfite. The remaining reagents are prepared within the laboratory. Caution must be taken since the shelf life of these reagents should not exceed 6 months unless otherwise noted. (1) 0.1 N Sulfuric acid : Add 2.8 mls concentrated acid to 1 liter distilled water. (2) 0.1 N Sodium hydroxide : Add 4 grams sodium hydroxide pellets to 1 liter distilled water. (3) Sodium sulfite solution : Prepare daily. Dissolve 1.575 g sodium sulfite up to one liter deionized water. (4) Manganese sulfate solution : Dissolve 364 grams manganese sulfate up to one liter deionized water. Slight heating and filtration may be necessary. (5) Glucose - Glutamic solution : Dissolve 75 mg glucose and 75 mg glutamic acid up to 500 ml deionized water. Sufficient stirring is required. (6) Alkali azide solution : In a 1 liter volumetric, dissolve 500 gram sodium hrdroxide pellets with 150 grams potassium iodide. When dissoliution is complete, add an additional 40 mls distilled water with 10 grams sodium azide. Caution must be taken when handling this solution. (7) 1 + 1 Acetic acid : 500 ml pure grade acetic acid is added to 500 ml deionized water with stirring. Caution must be taken since the temperature of the solution will increase rapidly. (8) Potassium iodide solution : Dissolve 10 grams potassium iodide in 100 ml volumetric flask with distilled water.

Sample Preparation...

Handling of the sample is critical to this procedure. The sample must be incubated within 48 hours of its original sampling time. Analysis after this point will have significant effects on the oxygen concentration within the sample and may often lead to less than accurate results. Usually, the DO of the sample will tend to decrease. When the sample is first brought in for analysis, it must be maintained at a temperature of approximatley 4 degrees Celsius. This is to ensure the fact that the oxygen concentration will remain constant and will also inhibit the further growth of organisms. Once in the lab, the pH of the sample must be adjusted for analysis. The desired pH for this procedure is between 6.5 and 7.5 where bacterial growth is

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possible. A 100 ml sample is usually adjusted with 0.1 N sulfuric acid or 0.1 N sodium hydroxide depending on the original pH of the sample. Once obtained, the sample content is checked to deterimine chlorine content. Chlorine must be removed from the sample because it introduces an interference with the dissolved oxygen .

Chlorine Content...

The chlorine content on a 100 ml neutralized sample can be determined by adding 10 ml potassium iodide solution and 10 ml 1 + 1 acetic acid as mentioned in the reagents section. When fully mixed, the addition of a starch indicator will denote the presence of chlorine if the sample turns a greyish - black. At this point, dropwise addition of freshly prepared sodium sulfite will diminsh the chlorine within the 100 ml sample. Once the chlorine has been dissipated, a new 100 ml sample must be neutralized and the same number of sodium sulfite drops must be added. At this point, the sample is ready for analysis. If no chlorine is detected in the sample after the 20 ml reagent addition, the addition of sodium sulfite is not necessary, and the sample must be neutralized again from a fresh sample.

Procedure...

Once reagents have been properly prepared, the sample is ready for analysis. The BOD procedure including the DO analysis is actually quite lengthy, so time maintenance is important. This portion can be carried out in four separate steps including carboy setup, adjustment of DO, preparation of seed inoculum, and BOD sample preparation. It is best to set up the carboy as soon as possible to ensure proper results. In addition, the BOD sample preparation is the last step of the procedure.

Carboy Set Up : The BOD procedure calls for two carboys to be used each time the procedure is carried out. The carboys will contain the water necessary for the procedure, and two are used instead of one to serve as a source of comparison amongst carboys. Also, it is a good idea to have two sources of water in case something goes terribly wrong with one of the carboys, there will be some sort of back up. To ensure that the two carboys involved in the procedure are free of contaminants, the carboys must first be rinsed with acid and water. Sufficient water should be rinsed to eliminate all traces of acid. Once the acid is flushed from the carboys, a small amount of bleach is added to eliminate excess organisms that may serve as sources of interference. The carboys are again flushed with adequate deionized water until the presence of bleach is eliminated. The carboys are then filled with pure water that has been finely filtered. Millipore water seems to work best in this procedure. The carboys should be filled up to supply atleast six liters for the first sample, and three liters for each successive sample. The six liters for the first sample are necessary because quality controls will also be included as part of the run. Once filled, one phosphate buffer pillow is added to the carboy per six liters water. These pillows are commercially available, and save the analyst time from preparing the reagents. After addition, the water solutions must be aerated until the point of saturation. Commonly, many laboratories will prepare this water the day before the procedure, but five hours prior to analysis appears to be sufficient. After aeration, the water is ready to be used to fill the BOD bottles, and must be capped until then.

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Seed Preparation : The seed solution must be set up some time before the BOD bottle are filled with water. This is done by adding 0.045 grams of a polyseed inoculum (or sometimes a BOD sample can be used as the inoculum) to 250 mls distilled water. The seed will not dissolve but it is important that the seed is stirred continously at moderate speed for about two hours. At approxiamtley 30 minutes prior to use, the seed solution is allowed to settle undisturbed. Caution must be taken not to disturb the seed particles because the liquid portion of the solution is used in the procedure. Remnants of actual seed within the prepared BOD bottles could greatly effect the results.

DO Preparation : The DO (dissolved oxygen) of the prepared carboy water must be determined to serve as a reference to all other sample and standard readings. This is most often accomplished by performing a Winkler titration on the carboy water, and adjusting the DO meter to this reading. This method is not contained in the BOD procedure, but rather comes from Standard Methods for the Examination of Water and Wastewater (Method 218B: Azide Modification: 1971). In my experience, we often used a pH meter with an electrode that could also determine the DO of the solution as our DO meter. The Winkler titration is carried out by first withdrawing three samples of water from each carboy. Caution must be taken that no air bubbles become trapped in the bottle. As a result, it is best to withdraw the water slowly while the bottles are tilted slightly. Once filled, one bottle from each carboy is set aside until later. The remaining four bottles are used in the actual titration. 2 mls manganese sulfate is added into each bottle under the surface of the water, followed by 2 mls alkali azide solution. The bottles are stoppered and shaken until a brown floc appears. The bottles are allowed to settle until the floc is halfway settled.

The bottles are then shaken again and allowed to settle. Once settled, 2 mls concentrated sulfuric acid is added down the neck of each bottle and the bottles are shaken again. At this point, the floc will disappear and the solutions should be amber in color. Now, the solutions are ready for titration. The solutions are first transfered to 500 ml ehrlenmeyer flasks. Each solution is titrated with 0.0375 N sodium thiosulfate until the solution turns a pale yellow. (Standard Methods suggests using 0.025 N sodium thiosulfate for a different volume of sample.) At this point, a few drops of starch indicator are added to turn the solution a dark blue. Titration continues until the solution turns clear. The volume of titrant used in mls directly corresponds to the DO of the sample. The average DO reading from each carboy is calculated and recorded. If the DO readings from each carboy set are not relatively close to each other (within 0.1 mls) the process must be repeated until consistent DO readings are obtained. The DO readings should normally fall between 6.0 and 9.0 mg/L. If values are greater than 9.0 mg/L, the carboy water must be aerated again to reduce the DO. Once the DO readings are calculated, the two bottles that were withdrawn at the beginning are now used. The carboy bottle from which the samples will be made up from is used to adjust the DO meter (in our case, the pH meter).

Once adjusted, the DO of the other bottle is measured to determine whether the meter is reading correctly. If the meter reading comes within 0.1 of the Winkler reading, the calibration is complete. If not, the entire Winkler procedure must be completed for both carboys.

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BOD Sample Preparation : Finally, the last step in the BOD procedure involves inoculating the sample with various dilutions along with standards and blanks for quality control. The following quality control must always accompany each BOD run : (1) 2 carboy water blanks, (2) 4 standards, (3) 2 seeded blanks and (4) optional control sample. Usually, many laboratories will include one set of QC for every ten samples. Additional QC is necessary for more than 10 samples. Preparation : (1) Water blanks - carboy water is withdrawn to the rim of the bottles. (2) Standards - 4, 6, 6, and 8 mls of standard solution are added to separate bottles. An additional 2 mls of seed solution is added to each bottle and the bottles are then filled to the rim with carboy water. (3) Seeded blanks - 2 mls of seed solution are added to each of 2 BOD bottles. The bottles are filled to the rim with carboy water. (4) Samples- 4-5 bottles are usually necessary for each sample. Some samples may have to be diluted in order for the DO range to be detected by the meter. Observation of the sample will usually give an indication to its dilution. Clean samples usually require small dilutions whereas wastewater samples will need high dilutions due to their high BOD values. Once reasonable dilutions have been determined, the specific volume of sample is added to each bottle along with 2 mls polyseed. The bottles are filled to the rim with carboy water. Once all the bottles have been filled, the initial DO's of each solution is determined on the meter and recorded. Once recorded, the bottles are capped with ground glass stoppers to avoid excess bubbles and capped. The bottles are placed in an incubator at approxiamtely 20 oC where they will remian for five days.

Analysis : After five days of incubation, the samples are ready to be analysed. The samples are removed from the incubator and allowed to equilibrate to room temperature. In the meantime, the analyst should calibrate the meter again with the carboy water as in the DO sample preparation section. It may be desired to use fresh carboy water for the calibration as in the carboy set up section. Once the meter is calibrated, the samples are read starting with the blanks and ending with the actual samples. The final DO of each solution is recorded and the initial and final readings will be used to calculate the BOD. The best results come about when the initial and final DO values for the blanks are similar indicating the absence of organisms and reliable equipment. The blank DO should normally be less than 0.2 mg / L. BOD Calculations...

The calculations for BOD take into account the unseeded blanks and the seeded solutions. These values must be subtracted out in order to obtain reasonable BOD results. The following calculations are taken from Standard Methods (Method 507: 1985, p. 531). (1) The BOD of the blanks are calculated by subtracting the final DO from the initial DO : BODblank = DO1 - DO2 (2) The BOD of the seeds are calculated by subtracting the final DO from the initial DO and multiplying this number by the dilution factor : BODseed = ( DO1 - DO2 ) x ( Dilution factor per 300 ml )

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(3) The BOD of sample and standards are calculated by subtracting the final DO from the initial DO and multiplying this number by the dilution factor. The final value is determined by substracting out the BOD blank and the seed blank for each delta DO. If the testing procedure was carried out correctly and the dilutions of the sample were made appropriately, the analyst should have obtained BOD values that are within a reasonable percent error and relative percent difference. Generally, values are discarded for a specific sample dilution if the final DO of the sample is < 1.0 mg/L of if delta DO is < 1.0 mg/L. This also stresses the importance of using different dilutions for each sample to key in on the appropraite BOD when little is known about how the sample will react and how high its BOD levels are.

Chemical Oxygen Demand...

The COD test is done by heating a portion of sample in an acidic chromate solution, which oxidizes organic matter chemically. The amount of chromate remaining (measured by a titration), or the amount of reduced chromium produced (measured spectrophotometrically), is translated into an oxygen demand value.

Biodegradability, toxins, and bacteria are not important, and the test is complete in about two hours. The figure will be higher than the BOD. Total Organic Carbon...

The TOC is done instrumentally. The organic carbon is oxidized to carbon dioxide by burning or by chemical oxidation in solution. The carbon dioxide gas is swept out and measured by infrared spectrometry or by redissolving it in water and measuring the pH change (the gas is acidic.) Both COD and TOC can often be correlated with BOD for a specific wastewater sample, but each wastewater is different. As a rough guide, the COD of a raw domestic wastewater is about 2.5 times the 5-day BOD. Solids...

Water, a liquid, can contain quite a bit of solid material, both in dissolved and suspended forms. The term "dissolved" implies that the individual molecules of a substance are mixed in among the water molecules. In practice, solids are classified as "dissolved" if they pass through a standard glass-fiber filter with about one micrometer pore size. Solids captured on the filter are, by definition, "suspended" solids. Solids which settle out of a water sample on standing for a period of an hour are defined as "settlable". Solids are also further classified as "fixed" or "volatile".

Fixed solids are basically the ash left over after burning the dried solids; volatile solids are those that are lost in this procedure. The sum of the two is referred to as "total". (This can be confusing, as the word "total" is also used in describing the sum of suspended and dissolved solids). Volatile solids are often used as an estimate of the organic matter present.

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Fig 1.3.5.Typical composition of solids in raw wastewater (floating solids are not included) Adapted, in part, from Crites and Tchobanoglous (1998) Significance...

Solids in wastewater contribute to sediment formation; volatile solids may be associated with oxygen demand. Suspended and dissolved Organic Solids have main role in the pollution (supporting the development of microorganisms like food sources and protecting microorganisms from enemies and disinfectants. Most technologies treatment are focusing in removal or elimination og organic solids in the wastewater, so the effluent is causing less problems in growing up pathogens and various microrganisms which create problems to the environment, to the ecology of the natural systems and to public health.

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Measurement of SOLIDS Total solids (TS) are determined by drying a known amount of a sample at a temperature of 103 to 105 C in a tared (pre-weighed) vessel, such as a porcelain dish, cooling in a dry atmosphere (in a container known as a desiccator), weighing on an analytical balance, subtracting the tare weight, and dividing by the original amount of sample. Results can be expressed in mg/L if the sample was originally measured out by volume; or percent by weight, if the sample was originally weighed.

If the sample is then burned in a furnace at about 500 C, cooled, and weighed, the

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fixed (FS) or volatile solids (VS) can be determined. If the original sample is filtered through a tared glass-fiber filter, which is then dried, the weight of the material captured on the filter is used to figure the total suspended solids (TSS). Burning the filter in the furnace allows measurement of volatile suspended solids (VSS) or fixed suspended solids (FSS). The dissolved solids (DS) can be estimated from the difference between the total solids and the total suspended solids, but the official method calls for drying the filtrate (the liquid which passes through the filter) in a dish at 180 C (and, of course, there are TDS, FDS and VDS). An estimate of total suspended solids can be obtained by an optical/instrumental measurement known as turbidity. The sample is placed in a glass tube; a beam of light is shined through it, and the light scattered at right angles to the beam is measured photometrically. In the same way that COD can be correlated with BOD, turbidity can be correlated with TSS; but the correlation will hold only for the particular sample from which it was derived. Similarly, an estimate of dissolved solids is often made by measuring the water's electrical conductivity. Pure water does not conduct electricity. If substances which dissociate into electrically charged ions are dissolved in the water, they will conduct a current, roughly proportional to the amount of dissolved substances.

Conductivity can be used to track sewage pollution. Note, however, that many organic materials dissolve in water without producing ions. So, while a salt solution may have a high electrical conductivity, a concentrated solution of sugar would go undetected by this method.

Nutrients...

Nutrients are usually thought of as compounds of nitrogen or phosphorus, although certainly other elements, such as iron, magnesium, and potassium are also necessary for bacterial and plant growth. Nitrogen occurs primarily in the oxidized forms of nitrates (NO3-) and nitrites (NO2-) or the reduced forms of ammonia (NH3) or "organic nitrogen" where the nitrogen is part of an organic compound such as an amino acid, a protein, a nucleic acid, or one of many other compounds. All of these can be used as nutrients, although the organic nitrogen first needs to decompose to a simpler form. Phosphorus is biologically important in the form of phosphate, the most highly oxidized state of the element. The most biologically available form is dissolved orthophosphate, (PO4-3). (In solution, there are up to three hydrogens attached to the molecule, each one decreasing the negative charge of the ion by one. How many hydrogens are attached depends on the pH. There are also condensed forms of phosphate, with more than one phosphorus atom per ion, such as pyrophosphate and polyphosphates. There are also organic phosphates, and all of these forms can be either dissolved or particulate (i.e., insoluble). The sum of all the forms is known as total phosphorus.

Significance...

These nutrients are important in natural waters because, in excess, they can cause nuisance growth of algae or aquatic weeds. In wastewater treatment, a deficiency of nutrients can limit the effectiveness of biological treatment processes. In some plants treating industrial wastewaters, ammonia or phosphoric acid must be added as a supplement.

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Measuremen of Ammonia Ammonia can be measured colorimetrically, by the Nessler or phenate methods, after distillation from an alkaline solution to separate it from interferences. It can also be determined by an electrode method, sometimes without distillation, since there are fewer interferences. Organically-bound, reduced nitrogen can be determined by the same methods after a digestion (the Kjeldahl digestion) which converts the nitrogen in those compounds to ammonia. The combination of ammonia and organic nitrogen is known as "Total Kjeldahl Nitrogen," or TKN. (TKN analysis is used for measuring protein content of animal feeds, as well.) Nitrite is determined colorimetrically. Nitrate can also be determined this way; the most popular way is by first reducing nitrate to nitrite chemically using cadmium, then analyzing the nitrite. There is an electrode method for nitrate, but it is not considered too accurate. Finally, ammonia (as the positively charged ammonium ion, NH4+), nitrate, and nitrite can be measured by ion chromatography, as well.

Phosphate can be measured by ion chromatography, also. Greater sensitivity, at lower cost, is obtained by colorimetric methods which measure dissolved orthophosphate. Some insoluble phosphates and condensed phosphates - so called "acid-hydrolyzable phosphate" - can be included by heating the sample with acid to convert these forms to orthophosphate. If the organic phosphate is to be included, to measure "total phosphate", then the sample must be digested with acid and an oxidizing agent, to convert everything to the orthophosphate form.

Chlorine...

The pure element exists as the molecule, Cl2, which is a gas or a liquid at normal temperatures, depending on the pressure. When dissolved in water, most of it reacts to form hypochlorous acid (HOCl) and hydrochloric acid (HCl) which make the water more acidic. The HOCl dissociates, to some extent, to form H+ and OCl-, called hypochlorite ion. (The HCl dissociates completely.) If there is enough alkalinity to react with the hydrogen ions produced and keep the pH around neutral, most of the chlorine will be in the form of hypochlorous acid and hypochlorite ion. Disinfection can be done using solutions of sodium hypochlorite, which produce the same substances in solution. Hypochlorite ion is not considered as strong a disinfectant as HOCl, so the pH can affect the disinfectant efficiency. Dissolved chlorine, hypochlorous acid, and hypochlorite ion, taken together, are all known as "free chlorine". Free chlorine can react with ammonia in solution to form compounds called chloramines, which are weaker disinfectants than free chlorine, but have the advantage of not being used up by side reactions to the extent that free chlorine is.

Free chlorine (and chloramines) also react with organic nitrogen compounds to form organic chloramines, which are even weaker disinfectants. The chloramines are termed "combined chlorine," and the sum of the free and combined forms are called

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"total chlorine". (Note that a large enough amount of chlorine can oxidize ammonia to nitrogen gas; this can be used as a chemical means of destroying ammonia) Significance...

Chlorine is the most commonly used disinfecting agent for drinking water and wastewater. It is coming into some disfavor because of toxic and carcinogenic byproducts, such as chloroform, which are formed when it reacts with organic matter present in the water. Unless reduced to chloride, chlorine itself is toxic to aquatic life in receiving waters. Pure chlorine liquid or gas is also a storage and transportation hazard because of the possibility of accidental releases to the atmosphere. Some treatment plants are switching to hypochlorite solution because it is safer to handle. Others are eliminating it entirely and using UV light or ozone for disinfection.

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Measuremen of Chlorine There are several choices for chlorine measurement, some of which can distinguish between free chlorine and the various chloramines. There are titrations involving visual, color-indicator endpoints, as well as electrochemically measured endpoints.

Some of them can be used to differentiate among the various forms of chlorine depending on whether iodide ion is added to the testing mixture. The indicator known as DPD (full name, N,N-diethylparaphenylenediamine) can be used to measure free or total chlorine both colorimetrically or as a titration indicator.

"Amperometric titration" is a sensitive electrochemical method.

Oil and Grease...

Is the name given to a class of materials which can be extracted from water using certain organic solvents. They can be of biological origin (animal fat, vegetable oil); they can be "mineral" (petroleum hydrocarbons); or they can be synthetic organic compounds. Fats and greases from restaurants and food processing industries can clog sewers, causing blockages and backups. Petroleum products can be toxic and flammable, and can coat surfaces and interfere with biodegradation by microorganisms in wastewater treatment plants. They are mostly biodegradable, especially biological oils and greases, but are a problem due to forming a separate phase from the water.

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Measurement of Oil and Grease

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The major method of analysis is liquid-liquid extraction. Currently, the chlorofluorocarbon known as CFC-113 is used, but is due to be phased out in favor of the hydrocarbon, hexane, because of the damage done by CFC's to the stratospheric ozone layer. In the procedure, the sample is acidified, and then shaken several times with the solvent. The solvent portions are combined and evaporated, and the residue is measured by weight. In a CFC solution, the concentration of the oil/grease can also be measured by infrared spectrophotometry without having to evaporate the solvent. To determine petroleum hydrocarbons alone, the extract solution can be treated with the material, silica gel, which absorbs the more polar biological compounds. A newer method, solid phase extraction, passes the water sample through a small column or filter containing solid sorbent material which absorbs the oil and grease. It is then desorbed from the sorbent using a solvent and analyzed as above.

Metals...

Chemically, metals are classified as elements which tend to lose electrons in a chemical reaction. As solids, they have easily movable electrons, which makes them good conductors of electricity and reflectors of light. In compounds, they tend to be positively charged, because they have lost electrons (which carry a negative charge), and they tend to bind with non-metals. This tendency makes some of them, such as iron and magnesium, biologically useful as part of biochemically active compounds like enzymes. Others, such as lead, cadmium, and mercury are highly toxic because they interfere with the normal operation of these biological compounds. The US EPA lists nine metals used in industry (arsenic, cadmium, chromium, copper, lead, mercury, nickel, silver, and zinc) as toxic "priority pollutant" metals.

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Measurement of metals There are numerous colorimetric methods for metals. Most of them are more useful in a purer medium, such as drinking water, than they are in wastewater, because of the presence of interfering substances. The most popular methods in use today involve one form or another of atomic spectroscopy, as described previously.

Another technique, X-ray spectroscopy, is useful primarily for solid samples. There are also electrochemical methods, like polarography and "anodic stripping voltametry" which are quite sensitive; but due to their complexity, they are confined mostly to research purposes.

Cyanide...

Cyanide is the name of an ion composed of carbon and nitrogen, CN -. It is used in the mining and metal finishing and plating industries - usually as the sodium or potassium salts, NaCN or KCN - because of its ability to bind very strongly to metals

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to form water-soluble complex ions. This same property makes it highly toxic to living things because it prevents the normal activity of biologically important, metalcontaining molecules. It is, however, biodegradable by some bacteria in low concentrations; and they can become acclimated to higher concentrations if given enough time. For unacclimated microorganisms in a wastewater treatment plant, however, a cyanide "dump" by an industry can lead to inhibition or even death, which can cause a severe "plant upset".

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Measurement of cyanide Cyanides are usually measured by a sensitive colorimetric / spectrophotometric procedure which can detect levels down to about 5 parts per billion in water. Since much of the cyanide in a sample is likely to be bound to metal ions, a digestion / distillation procedure is necessary to measure "total" cyanide. Cyanide can also be measured by ion chromatography or an electrode method, though the latter is not considered too accurate.

Toxic Organic Compounds...

An organic compound is any compound which contains carbon, with the exception of carbon monoxide and carbon dioxide, carbonates, or cyanides. Organic compounds contain chains and/or rings of connected carbon atoms, often with other elements attached. There are millions of possible compounds, with many useful properties.

Many are biologically active, since all living things are made up of organic molecules.

Industries use and produce thousands of organic compounds in manufacturing such items as plastics, synthetic fibers, rubber, pharmaceuticals, pesticides, and petroleum products. Some of the compounds are starting materials; some are solvents; some are byproducts. The US EPA lists 116 of them as toxic "priority pollutants"; many states have longer lists. One of the major groupings is volatile organic compounds (VOC's), many of which are chlorine-containing solvents. There are also petroleum hydrocarbons and starting materials for plastics, dyes, and pharmaceuticals. The "semi-volatile" group include solvents, PAH's (polycyclic aromatic hydrocarbons, like naphthalene and anthracene which are coal tar constituents), as well as pesticides (especially chlorinated pesticides) and PCB's (polychlorinated biphenyls, which were formerly used in electrical transformers and other products).

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Measurement of Toxic Organic Compounds...

Most of these are analyzed routinely by gas chromatography (GC), often followed by mass spectrometry (MS) for identification. HPLC is also used for some analytes. A technique which is becoming available for field measurements for some of these compounds is immunoassay, sometimes called ELISA, for "enzyme-linked immunosorbent assay". This method, which produces a color reaction related to the concentration of the target compound, or family of compounds, is portable, relatively inexpensive and does not require a great deal of training. It is in use more for surveying hazardous waste sites, however, than for water analysis.

Alkalinity Alkalinity in wastewater results from the presence of the hydroxides [OH -], carbonates [CO3-], and bicarbonates [HCO-] of elements such as calcium, magnesium, sodium, potassium, and ammonia. Of these, calcium and magnesium bicarbonates are most common. Borates, silicates, phosphates, and similar compounds can also contribute to the alkalinity. The alkalinity in wastewater helps to resist changes in pH caused by the addition of acids. Wastewater is normally alkaline, receiving its alkalinity from the water supply, the groundwater, and the materials added during domestic use. The con-centration of alkalinity in wastewater is important where chemical and biological treat-ment is to be used, in biological nutrient removal, and where ammonia is to be removed by air stripping.

Moreâ&#x20AC;Ś Alkalinity is determined by titrating against a standard acid; the results are expressed in terms of calcium carbonate, mg/L as CaCO3. For most practical purposes alkalinity can be defined in terms of molar quantities, as

Adapted, in part, from Crites and Tchobanoglous (1998) Pathogenic Microorganisms...

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Sewage contains large numbers of microbes which can cause illness in humans, including viruses, bacteria, fungi, protozoa and worms (and their eggs or ova). They originate from people who are either infected or are carriers. While many of these can be measured directly by microscopic techniques (some after concentration), the analyses most commonly performed are for so-called "indicator organisms". These organisms, while not too harmful themselves, are fairly easy to test for and are chosen because they indicate that more serious pathogens are likely to be present.

For instance, wastewater treatment plants are often required to test their effluents for the group known as "fecal coliforms", which include the species E. coli, indicative of contamination by material from the intestines of warm-blooded animals. Water supplies test for a more inclusive group called "total coliforms", and in some cases, for general bacterial contamination (heterotrophic plate count, or HTP).

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Measurement of Pathogenic Microorganisms The two most commonly used methods of analysis for indicator organisms are the multiple tube fermentation technique and the membrane filter procedure. In the first method, a number of tubes containing specific growth media are innoculated with different amounts of the sample and incubated for a particular time at a prescribed temperature. The appearance of colors, fluorescence, or gas formation indicates the presence of bacteria belonging to the target group. The number of organisms per 100 mL in the original sample is estimated from most probable number (MPN) tables, which list the values of MPN for different combinations of positive and negative results in tubes which contained different initial volumes of the sample. Often, positive results must be confirmed by further innoculation of small amounts of material from the positive tubes into tubes containing a different media, which can extend the test to several days. The second technique involves filtering a known volume of sample through a membrane filter (made of a material such as cellulose acetate) which has a small enough pore size to retain the bacteria. The filter is then placed in a dish of sterile nutrient media, either soaked into an absorbent pad or in a gel such as agar, and sealed. The dish is incubated for the prescribed time and temperature. The media contain a colored indicator which will identify the target bacteria. Each bacterium in the original sample will result in a colony after incubation, which is large enough to see without a great deal of magnification. The concentration in the sample can be determined by direct count of the colonies, knowing the volume of sample used. In some cases, these colonies require further confirmation. Detection and enumeration of HTP or of specific pathogenic bacteria, such as Salmonella, E. coli or Enterococcus can be done by similar methods, but utilizing specific growth media for each type. Viruses are usually measured by concentration, followed by addition to cultures of cells which they infect and counting the number of plaques formed due to cell destruction. Pathogenic protozoa and ova of multicelled organisms are

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determined by concentration and direct counting under the microscope, often with the aid of fluorescent staining compounds. Besides, direct observation, identification of pathogenic microorganisms can be done by standard techniques used in clinical laboratories involving observing reactions in a battery of different indicating media.

Some newer methods use chromatography to identify patterns of compounds which serve as "fingerprints" for certain bacteria; DNA analysis is another recent innovation. Most wastewater treatment plants, however, confine their testing to simply counting the numbers indicator bacteria.

Figure 1.3.6. Interrelationships of solids found in water and wastewater. In much of the water quality literature, the solids passing through the filter are called dissolved solids. (Tchobanoglous and Schroeder, 1985.)

(*) Adapted from Wastewater Engineering Treatment and Reuse Metcalf & Eddy (2003),

Table 1.3.10 Particle classification in the TOTAL SOLIDS, related with their size and their form in the wastewater

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Fig 1.3.7 Classification of solids found in medium strength wastewater (Metcalf and Eddy, Inc.1991.)

Table 1.3.11.Odorous Compounds Associated With Untreated Wastewater

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Fig. 1.3.6 Main steps in a indicative flow sheet of a conventional wastewater treatment plant, showing the constitutes removed by each step

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Table 1.3.11 Occurrence of some pathogens In urine, a faecea and sullage b Pathogen

Common name for infection caused

Present in: urine faeces sewage

Bacteria: Escherichia coli

diarrhoea

*

*

*

Leptospira interrogans

leptospirosis

*

Salmonella typhi

typhoid

*

*

*

Shigella spp

shigellosis

*

Vibrio cholerae

cholera

*

Poliovirus

poliomyelitis

*

Rotaviruses

enteritis

*

Viruses: *

Protozoa - amoeba or cysts: Entamoeba histolytica

amoebiasis

*

*

Giardia intestinalis

giardiasis

*

* *

Helminths - parasite eggs: Ascaris lumbricoides

roundworm

*

Fasciola hepatica

liver fluke

*

Ancylostoma duodenale hookworm

*

*

Necator americanus

hookworm

*

*

Schistosoma spp

schistosomiasis

*

*

Taenia spp

tapeworm

*

*

Trichuris trichiura

whipworm

*

*

*

a

Urine is usually sterile; the presence of pathogens indicates either faecal pollution or host infection,principally with Salmonella typhi, Schistosoma haematobium or Leptospira.

Table 1.3.12. Survival Of Excreted Pathogens (at 20-30°C) Type of pathogen

Survival times in days In faeces, nightsoil In fresh water and and sludge sewage

In the soil

On crops

<100 (<20)

<60 (<15)*

Viruses Enteroviruses

<100 (<20)

<120 (<50)

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Bacteria Faecal Coliforms

<90 (<50)

<60 (<30)

<70 (<20)

<30 (<15)

Salmonella spp.

<60 (<30)

<60 (<30)

<70 (<20)

<30 (<15)

Shigella spp.

<30 (<10)

<30 (<10)

-

<10 (<5)

Vibrio cholerae

<30 (<5)

<30 (<10)

<20 (<10) < 5 (<2)

<30 (<15)

<30 (<15)

<20 (<10) <10 (< 2)

<30 (<15)

<30 (<15)

<20 (<10) <10 (< 2)

Many

Many

Many

Months

Months

Months

Protozoa Entamoeba histolytica cysts Helminths Ascaris lunbricoides eggs

* Figures in brackets show the usual survival time.

Source: Feachem et al. (1983)

<60 (<30)

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ASSIGNMENTS SECTION

ASSIGNMENTS SECTION 1.

QUESTIONS:

Write your answers 1.1A How did many receiving waters become polluted?

1.1B Why must municipal and industrial wastewaters re¬ceive adequate treatment?

1.1C Why is it important that the operator be present during the construction of a new plant?

1.1D How does the operator become involved in public relations?

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SUGGESTED ANSWERS:

1.1A Receiving waters became polluted by a lack of public concern for the impact of waste discharges and by dis¬charging wastewater into a receiving water beyond its natural purification capacity.

1.1B Municipal and industrial wastewaters must receive adequate treatment to protect receiving water users.

1.1C The operator should be present during the construc¬tion of a new plant in order to become familiar with the plant before the operator begins operating it.

1.1D The operator becomes involved in public relations by explaining the purpose and operation of the plant to visitors, civic organizations, school classes, news reporters, and city or district representatives.

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ASSIGNMENTS SECTION

ASSIGNMENTS SECTION 2.

QUESTIONS:

Write your answers 1.2A What causes oxygen depletion when organic wastes are discharged to the water?

1.2B What kind of bacteria cause hydrogen sulfide gas to be released?

1.2C Which are the Main Impacts of Eutrophication?

1.2D What is a combined sewer overflow (CSO)?

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1.2E What is a sanitary sewer system?

1.2F Which are the main components of a pressure sewer (Grinder, GP) system?

1.2G Which are the main components of a vacuum sewer system?

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SUGGESTED ANSWERS:

1.2A Organic wastes in water provide food for the bacteria. These bacteria require oxygen to survive and consequently deplete the oxygen in the water in a way similar to the way oxygen is removed from air when people breathe.

1.2B Hydrogen sulfide gas is produced by anaerobic bacteria.

1.2C Main Impacts of Eutrophication may be: •

Increased biomass of phytoplankton

•

Toxic or inedible phytoplankton species

•

Increases in blooms of gelatinous zooplankton

•

Increased biomass of benthic and epiphytic algae

•

Changes in macrophyte species composition and biomass

•

Decreases in water transparency (increased turbidity)

•

Colour, smell, and water treatment problems

•

Dissolved oxygen depletion

•

Increased incidences of fish kills

•

Loss of desirable fish species

•

decreased biodiversity

•

Reductions in harvestable fish and shellfish

•

Decreases in perceived aesthetic value of the water body

1.2D. A combined sewer overflow (CSO) is the discharge of wastewater and stormwater from a combined sewer system directly into a river, stream, lake, or ocean.

1.2E A sanitary sewer (also called a foul sewer) is a separate underground carriage system specifically for transporting sewage from houses and commercial buildings to treatment or disposal.

1.2F A pressure (GF) sewer system is composed of: 1. Pumping Unit (This includes a small pump, storage tank and level monitors)

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2. Boundary Valve Kit 3. House Service Line , (a small diameter pipe connects your property drain to the pumping unit on your property).

4. Control Panel

1.2G A vacuum sewer system is composed of: 1. Collection chambers and vacuum valve units 2. Monitoring system for collection chambers and vacuum valve units 3. Vacuum sewer lines

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ASSIGNMENTS SECTION

ASSIGNMENTS SECTION 3.

QUESTIONS:

Write your answers

1.3A What are the main actions for correct operation of the plant by the operators?

1.3B Where do the disease-causing bacteria in wastewater come from?

1.3C What is the term that means "disease-causing"?

1.3D What is the most frequently used means of disinfecting treated wastewater?

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1.3E Which the main components of the wastewater flow?

1.3E Total solids consist of

and

solids,

both of which contain organic and inorganic matter.

1.3F Why is it necessary to measure settleable solids?

1.3G An Imhoff cone is used to measure solids

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SUGGESTED ANSWERS:

1.3A All the works and actions needed for a very good operation of a WWTP: (1) correct operation of the plant, according the environmental laws and rules and especially all the outputs to comply with the environmental terms approved for the operation of the WWTP (2) correct operation of the plant with hygienic and safe working conditions .

(3) correct operation of the equipment .

(4) for all actions in normal , irregular or emergency or conditions, according the instructions and orders by the manager of the plant, responsible for the Operation.

(5) the sampling, samples preparation and transportation to the lab for analysis (6) all the basic tests and analysis, if this is in their responsibilities (7) calendar keeping for all the daily works, all the events and actions (8) reports with all the results.

1.3B Disease-causing bacteria in wastewater come from the body wastes of humans who have a disease.

1.3C Pathogenic means disease-causing.

1.3D Chlorination is the most frequently used means of disinfecting treated wastewater.

1.3E The main components of the wastewater are: 1)Domestic (also called sanitary) wastewater.

2)Industrial wastewater.

3) Infiltration/inflow waters 4)Stormwater.

1.3F Total solids consist of DISSOLVED and SUSPENDED solids, both of which contain organic and inorganic matter.

1.3G Settleable solids must be measured to determine the efficiency of settling basins. This amount must also be known to calculate loads on settling basins, sludge pumps, and sludge handling facilities for design and operational purposes. (You should have recognized the need to know the efficiency of settling basins.)

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1.3H An Imhoff cone is used to measure SETTLEABLE solids.

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