C Factor—Kenneth Enlow

C FACTOR Disinfection: Part Two

Kenneth Enlow

President, FWPCOA

Greetings everyone. August brings us the oppressive heat and humidity we are accustomed to, as well as our hurricane season. Keeping our utilities operating efficiently and safely is always job one.

July’s C Factor focused on the history of disinfection. This month’s column is going to review disinfection and the disinfection methods that we practice today.

What is Disinfection?

Disinfection Versus Sterilization

Disinfection is the process designed to kill or inactivate most microorganisms, including all pathogenic (disease-causing) bacteria. Sterilization is the complete destruction of all organisms, but it is not necessary and would be rather difficult for water utilities to perform. When done properly, disinfection is sufficient to ensure that the water provided to your customers is safe to drink, which is what the term potable means. We also want to provide a product to our customers that’s palatable, meaning it smells good, taste good, and looks good.

So, what are examples of some of the pathogenic organisms transmitted by water that are targeted when disinfecting? S Bacteria • Legionella • Salmonella • Bacillus • Cholera

S Viruses • Norovirus • Polio • Hepatitis

S Intestinal Parasites • Giardia lamblia • Cryptosporidium

Disinfection Standards

The treatment of water for the inactivation of pathogens is defined by the U.S. Environmental Protection Agency (EPA), which is responsible for setting and enforcing drinking water standards.

The Safe Drinking Water Act (SDWA) is responsible for: S Setting standards for primary and secondary contaminants. S Defining what to do if a maximum contaminant level (MCL) is exceeded. S Defining standards based on raw water source and treatment methods. S Setting standards for disinfection byproducts.

Effective and proper disinfection is a balance between providing the best protection against pathogens and control of disinfection byproducts. Florida Administrative Code (FAC) 62-550, Disinfection Byproducts, uses the EPA Federal Register Subpart L, 40 CFR Part 141, as guidance for MCLs for disinfection byproducts.

Organics from source water combine with chlorine compounds to form byproducts, specifically, trihalomethanes (THMs) and haloacetic acids (HAA5). There are four specific THMs compounds and five defined HAA5, but the EPA standard for MCL regulates them on a combined total.

The MCLs for total trihalomethanes (TTHMs) and HAA5 are: S TTHMs - 0.08 mg/L or 80 parts per billion (ppb) S HAA5 - 0.06 mg/L or 60 ppb

The THMs and HAA5 are suspected of causing liver, kidney, and reproductive system damage; cancer in humans; and other health issues. These standards apply to all community water systems that disinfect their water.

Other disinfectant byproducts that are regulated are bromate and chlorite. Bromate can form when using ozone as a disinfectant. With the presence of bromide, ozone will combine with it to produce bromate. The pH has a significant effect on the formation of bromate above a pH value of 6.5.

The MCL for bromate is: S Bromate - 0.010 mg/L

Chlorite byproducts are usually a result of disinfection with chlorine dioxide or with hypochlorite.

The MCL for chlorite is: S Chlorite - 1 mg/L

Factors Influencing Disinfection

There are many factors that can influence the effectiveness of disinfection: S pH – Generally, the lower the pH, the faster the disinfectants work. S Temperature – The higher the temperature of the water, the more efficient it can be treated.

Lower temperatures require longer contact time. S Turbidity – High turbidity greatly reduces disinfectant efficiency and can create a higher demand for chlorine. S Organic Matter – Consumes disinfectant while forming byproducts, such as THMs and HAA5. S Inorganic Matter – Free ammonia in the water can combine with oxidizing chemicals, like chlorine, causing a partial loss of disinfection power. Silt and other debris can create demand as well. S Reducing Agents – Iron, hydrogen sulfide, manganese, and nitrite can react with the chlorine, causing greater demand, as well as produce solids during the oxidation process. S Microorganisms – The higher the number of microorganisms, the greater the demand for disinfectant. Resistance varies greatly with different microorganisms.

Removal of Microorganisms Through Treatment

These processes can reduce the influence (demand) on disinfection: S Coagulation can remove 90 to 95 percent of pathogenic microorganisms. S Sedimentation can remove 20 to 70 percent of pathogenic microorganisms. S Filtration can remove 20 to more than 99 percent of pathogenic microorganisms.

When determining the required inactivation of pathogens for a particular system, these treatment processes provide credits toward the inactivation.

Disinfection Considerations

Some considerations to take into account are the different types of disinfectants available and what is suitable for the characteristic of your system based on source water and other factors, like residence time. S Free Chlorine – The most common disinfectant in the absence of source water organics where disinfection byproducts are not an issue. S Monochloramine – Ammonia plus chlorine is longer-lasting and more stable than free chlorine. Monochloramines can reduce the production of disinfection byproducts. S Chlorine Dioxide – Not commonly used and can increase chlorite and chlorate. There is a maximum residual disinfection level (MRDL) of 0.8 mg/L for chlorine dioxide residual. S Ozone and Ultraviolet (UV) – Used mostly in plants as a primary disinfectant; they are very effective when applied properly. Ozone and UV do not produce a disinfection residual and therefore are not suitable for secondary disinfection.

When applied, disinfection has two specific purposes: primary disinfection is applied to achieve the inactivation of pathogens, and secondary disinfection is applied to maintain a barrier against recontamination or regrowth within the water distribution system.

A system must maintain a residual in the distribution system per FAC 62-555350 (6). A minimum residual of 0.2 mg/L for free chlorine and 0.6 mg/L for combined or total chlorine is required. The MRDL for free chlorine and monochloramines is 4 mg/L. By maintaining a residual, the system can prevent contamination due to new main installations, cross connections, main breaks, and biofilms.

Monochloramine is more effective in controlling biofilm and is a more-stable disinfectant than free chlorine, as well as helping to control disinfection byproducts. An absence of residual in the distribution system is indication of contamination that has created a high demand for the disinfectant.

Disinfectants may be the cause of taste and odor and other issues in the distribution system. Free chlorine may cause a chlorinous taste and odor, especially if overdosed. Dichloramine causes taste and odor problems and poor disinfection, but increasing the chlorine dose can remedy this problem. Free chlorine may increase copper corrosion and monochloramine may be the cause of deterioration of some types of rubber products.

When disinfecting with chlorine, it should be added until the demand is met. The chlorine demand is the amount of chlorine used to react with organic and inorganic materials to form chlorine compounds. When the reactions with these materials stop, the chlorine demand has been satisfied. Adding additional chlorine will leave a residual. The residual is the total of all compounds with disinfecting properties, plus any remaining free (uncombined) chlorine. A residual indicates that all reactions have taken place and there is available chlorine to kill microorganisms. S Dose = demand + residual S Residual = dose – demand S Demand = dose – residual

Reactions associated with breakpoint chlorination.

Breakpoint Chlorination Explained

- As more chorine is added, monochloramine and chlororganics are formed, shown in segment 2. - Continuing to add chlorine forms dichloramine and destroys monochloramines in segment 3. - Additional chlorine will oxidize ammonia to trichloramine at the beginning of segment 4.

This is referred to as breakpoint. Any further addition of chlorine will result in free chlorine residual.

I would also make note here that in segment 2 is where the monochloramine is formed. This is where the chlorine-to-ammonia ratio would be maintained for chloramination. This ratio is usually maintained between 3:1 and 5:1 chlorine to ammonia.

One of the potential issues for chloraminated systems, or any system with excessive free ammonia, is nitrification. Ammonia can be released when it’s unbound from the chloramine in the distribution system. Nitrification occurs when free ammonia breaks down into nitrite (NO2) and nitrate (NO3). This is caused by Nitrosomonas bacteria eating the free ammonia (NH3) that is present in the system and converts it to nitrite. Then Nitrobacter bacteria eat nitrite and convert it to nitrate. High nitrates are left in water, which can cause health issues for humans and increased waterborne bacteria aftergrowth.

The chart at the top of the page explains the reactions associated with breakpoint chlorination. - When chlorine is first added to water, it’s destroyed by reducing compounds, which is illustrated in segment 1.

Nitrification Prevention and Control

Nitrification can be controlled by following proper treatment techniques and a well-defined distribution system maintenance program. Continued on page 14

Chlorine tablets.

Continued from page 13

Signs of Nitrification

The following is a list of some signs of nitrification: S A decrease in ammonia levels S A decrease in total chlorine level S A decrease in pH (release of H+ ions when ammonia breaks down) S An increased nitrite levels S An increase in heterotrophic plate count

Methods of Controlling Nitrification

The following are some preventive measures to take to help control nitrification: S Decrease detention time in the system, especially in warmer months. S Decrease free ammonia by increasing chlorine-to-ammonia ratios from 3:1 to 5:1. S Establish a distribution system flushing program. S Flushing reduces detention time. S Velocity removes sediments and biofilms that harbor bacteria. S Flushing draws higher residuals into the problem area. S Increase chloramine residual in the distribution system to greater than 2 mg/L.

Blending chloraminated water with free residual systems may drop or lose free residual if free ammonia is present. When disinfecting with chlorine compounds the monochloramines will react with the free chlorine before getting a free residual. Always measure total chlorine residual when testing for chloramines.

Distribution System Maintenance Disinfection

Anytime a distribution system needs maintenance or repair, maintaining the integrity of the rest of the system needs to be considered. Preventing contamination of the existing system through proper isolation and disinfection of repairs and new construction is necessary to maintain that system’s integrity.

Main break.

Disinfection of Water Mains

Water main disinfection is defined in Standard Methods, AWWA Standard C651-14, Disinfection of Water Mains.

Procedures to Follow Before Disinfection S Preventive Measures – Keep outside debris out of pipe. S Preliminary Measures – Flush before disinfecting and clean fittings and valves before disinfecting.

Disinfection Alternatives

Deciding which disinfectant is right for your disinfection process depends on the method you choose. The three primary chlorine compounds used are: S Chlorine Gas – 100 percent concentration S Calcium Hypochlorite – 65 percent concentration S Sodium Hypochlorite – 10 to 12 percent concentration

Decide Which Disinfection Method to Use

AWWA Standard C651-14 defines three methods of disinfection with chlorine: S Tablet Method – Place calcium hypochlorite tablets in the water main as it is being installed

Microbe.

and then fill the main with potable water when completed. Place calcium hypochlorite granules at the upstream end of the first section, at each branch main, and at 500-feet intervals.

Fill the pipe and hold for 24 hours. You must have a detectable residual. S Continuous Feed Method – Place calcium hypochlorite granules during construction and then fill with potable water. Hold for 24 hours.

You must have 10 mg/L chlorine residual after 24 hours. Optionally, calcium hypochlorite granules can be placed at pipe sections before flushing. Flush the main at a velocity of 2.5 feet/second. Add potable water to the main and add chlorine at a rate to have no less than 25 mg/L residual. Use a chlorine solution of mixing calcium hypochlorite or use sodium hypochlorite and continuously feed until the entire main is chlorinated and hold for 24 hours. Open and close valves and hydrants to ensure contact with the chlorine. After 24 hours the entire main must have a chlorine residual of 10 mg/L. S Slug Method – Place calcium hypochlorite granules in the main during construction.

Flush the main and then slowly flow a slug of water with a concentration of 100 mg/L of chlorine. The main must be exposed to the highly chlorinated water for a minimum of three hours. If the residual drops below 50 mg/L the procedure must stop and the feed started again at the beginning to maintain 100 mg/L. Operate valves and fittings to make sure they are exposed. Flush the main until the water reaches normal distribution chlorine residual.

Disinfection for Final Connection to Existing Mains S Connections equal to less than one pipe length (<18 feet) – Spray or swab with a 1 to 5 percent chlorine solution just prior to installation. S Connections greater than one pipe length (>18 feet) – Pipe is to be set above ground, disinfected, and bacteriological samples taken.