Chloramination and Nitrification in the Distribution System

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1 Chloramination and Nitrification in the Distribution System Presented by: Debra Cerda Public Drinking Water Section TCEQ 13th Annual Water/Wastewater 2004 Public Drinking Water Conference August 3-4, 2004

2 Why? Why do we need alternate disinfection? < Chlorine is great - BUT... < Chlorine interacts with Í Total organic carbon (TOC) and bromide Í To form potentially carcinogenic disinfection byproducts (DBPs) < MAY Need to disinfect with something else

3 Risk Reduction Balance acute and long-term health effects < Try to KEEP ADEQUATE disinfection < While NOT forming DBPs < Optimize public health protection

4 Balancing Risk Risk of waterborne disease Risk of cancer RISK DISINFECTION

5 Advantages Widely used in Texas < CAN use in plant < CAN use in distribution system Í Last longer than free chlorine Í Forms very little THMs Í Somewhat less HAA than free chlorine < Just add ammonia

6 Disadvantages Issues with use < Weaker Í Need more contact time to get inactivation credit in plant < Can t just add ammonia Í Ratio is important < Health effects Í Dialysis patients and fish Í Nitrification

7 Must Know < Ammonia Concentration in water < Form of ammonia & chlorine to be added (gaseous, aqueous, liquid) Í Percent chemical in solution Cl 2 = 100% LAS = 24% of sol n Í Percent nitrogen or chlorine in chemical LAS = 21% Nitrogen < Need to adjust calculations accordingly

8 Design Considerations < Only credit for post-ammoniation < Must provide adequate mixing < Pumps must be designed for that specific chemical

9 Chloramine Chemistry Ratio < Breakpoint chlorination < Keep Cl2 : NH4-N ratio at 3:1 to 5:1 < OR! Í Loss of residual Í Taste and odor Í Regrowth in distribution system

10 Breakpoint Curve Monochloramine 5 : 1 3:1 4:1 >8:1 7 : 1 Added chlorine (fixed N)

11 Cl 2 :NH 4 -N Ratios < 0-3:1 Í Free ammonia Í Leads to nitrification < 5:1 Í Loss of residual Í Taste and odor < >7:1 Í Free chlorine DBPs

12 How will Chloramines Effect My Plumbing? < Less harmful to iron, steel and copper than free chlorine < Have not seen damage to gaskets and other rubber pipeline materials < Can degrade elastomeric plumbing materials Í Inexpensive rubber toilet flappers

13 Nitrification How does it occur? < Two step process Í Ammonia converted to nitrite by Ammonia Oxidizing Bacteria (AOBs) Í Which can then be converted to nitrate by Nitrogen Oxidizing Bacteria (NOBs) < Often incomplete- only first step occurs

14 Nitrification How does it occur? < Chloramine decay releases ammonia < Risk increases Í with temperature Í With increasing distance into distribution system Í As disinfectant demand increases

15 Nitrification Why be concerned? < Acute health risk to infants up to six months of age Í Methemoglobinemia (blue baby syndrome) < Nitrite and bacterial growth consume disinfectant < 1996 report estimated 63% of chloraminating utilities showed signs of nitrification in distribution system

16 Nitrification Monitoring Strategy < Parameters- Í Heterotrophic Plate Counts (HPCs) Í Free and total ammonia Í Nitrite and nitrate Í Chlorine dose Í Chloramine residual Í Addt l: Temperature, dissolved oxygen, alkalinity, ph, TOC, DOC Í Fish

17 Nitrification Monitoring Strategy < Sampling locations: Í Raw water Í Finished water Í Reservoirs Í Dead-end mains Í Routine coliform monitoring stations

18 Preventative Measures < Monitor and control the ratio < Decrease distribution residence times < Periodic changes to free chlorine < Flushing programs < Booster stations to increase chloramine residual and decrease free ammonia concentration

19 No mixing chlorine and chloramine in distribution system Cl 2 free chlorine NHCl 3 chloramine WHAT is the ratio??? You don t know. Don t do it. You don t know. Don t do it.

20 Blending < Free chlorinated water + chloraminated water = NO DISINFECTANT OR High DBPs Í Blend in reservoir or storage tank Í Measure chlorine at outlet and add ammonia to reach desired ratio < No free blending in distribution system

21 Purchased Water Systems Receiving Chloraminated Water < Choice 1 - Do nothing Í Chloramines may provide the desired residual Í Run tests to assure DLQOR

22 Purchased Water Systems Receiving Chloraminated Water < Choice 2 - Booster Chlorinate Í Chloramine decay produced ammonia Í Measure level in incoming water Í May be able to add a small amount of chlorine to recombine with ammonia Í Run tests to assure

23 Purchased Water Systems Receiving Chloraminated Water < Choice 3 - Booster Chloraminate Í Measure chlorine and ammonia levels in incoming water Í Add appropriate amounts of ammonia and chlorine to form 3:1 to 5:1 ratio. Í Measure free and combined chlorine in distribution system

24 Conclusion < Chloramines form less DBPs BUT can cause other issues < Cl:N Ratio is extremely important < Measure incoming chlorine and ammonia concentrations

25 TCEQ Public Drinking Water Section (512)

EPB 311- Strategies for Dealing with Groundwater Treatment Systems Having High Natural Ammonia

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