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Review of the Production and Control of Disinfection By-Products (DBP’s)

Review of the Production and Control of Disinfection By-Products (DBP’s). Goals of DBP Review. Review Disinfection By-Product MCL’s Review How DBPs are Formed Review Water Sources and ID Conditions that Contribute to a DBP Problem Identify Measuring Parameters Associated with NOM and TOC

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Review of the Production and Control of Disinfection By-Products (DBP’s)

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  1. Review of the Production and Control of Disinfection By-Products (DBP’s)

  2. Goals of DBP Review • Review Disinfection By-Product MCL’s • Review How DBPs are Formed • Review Water Sources and ID Conditions that Contribute to a DBP Problem • Identify Measuring Parameters Associated with NOM and TOC • Identify DBP Best Management Practices • Review DBP Troubleshooting Guide • Conduct Interactive Role Playing Exercise

  3. DEP MCL Requirements for DBP’s TTHM, HAA5, Chlorite and Bromate • TTHM .080 mg/l • HAA5 .060 mg/l • Chlorite 1.0 mg/l* • Bromate 0.010 mg/l ** * associated with the use of Chlorine Dioxide ** naturally occurring precursor in systems near saltwater, associated with use of Ozone

  4. Disinfection Byproducts Formation NOM + Cl2 THMs + HAAs + Other DBP Compounds • Disinfection Byproducts (DBP) are produced by the reaction of free chlorine with natural organic material (NOM) found in source waters. • The amount of organic materials (NOM) can be approximated by the amount of Total Organic Carbon (TOC) present. • The portion of the NOM that forms the DBP’s is generally the dissolved portion (DOC is that part of the TOC that can be identified by first removing the NOM that is retained on a 45 micron filter)

  5. Sources of Natural Organic Material (NOM) in Surface Water • Rain Events wash organic matter into receiving body. • Flooding reverses flow gradients in upper aquifers • Cavities and Fissures in Karst Conditions allow surface intrusion • Poor Sanitary Conditions, i.e., broken seals, abandoned wells, poor locations, result in intrusion • Ground Water that has high NOM content is indicative of the intrusion from Surface Water • Sedimentation, biogrowth or poor flushing practices in distribution systems increase organics concentration.

  6. Use of Different Carbon Surrogates

  7. Raw Water Considerations • DBP Problem analysis always starts with a well investigation! • Generally surface waters or ground waters under the direct influence of surface water (UDI) will have higher levels of organic materials (TOC.) • Surface waters have higher treatable humic content than GW • If Surface water mixes with ground water, each well may experience different levels of TOCs. • The humic content can be approximated by using SUVA.

  8. Organic Carbon (TOC) or Precursors in Natural Waters mg/l Mean Surface Water 3.5 Sea Water Ground Water Surface Water Swamp Wastewater Wastewater Effluent .1 .2 .5 1.0 2 5 10 20 50 100 200 500 1000

  9. Typical Values of TOC for Various Waters

  10. Thickness and Extent of Intermediate Aquifer Confinement • The Confining Unit restricts flow of groundwater between the Surficial Aquifer and Floridan Aquifer when present. • Protects underlying Floridan Aquifer, Florida’s primary source of drinking water, from potential contamination N

  11. Karst Features N • Karst is a type of topography that is characterized by depressions caused by the dissolution of limestone. • These features include caves, sinkholes, springs, and other openings. • In karst areas, interactions between surface water and groundwater are extensive and groundwater quality can degrade quickly. Light areas indicate Karst features

  12. Reducing the Production of Disinfection By-Products • Eliminating Sources of Surface Water into Production Wells • Selecting Well Blends with Lower DBPs • Removing Precursor Material within treatment process • Changing the Point(s) of Chlorine Application • Lowering the Chlorine Dose and/or Residual • Using Alternate Disinfection Strategies • Ensuring the WTP processes are absent of organic growth (ie. Ion Exchange and Activated Carbon Systems) • Ensuring Water Tank Turnover • Reducing Distribution System Water Age • Flushing water in slow moving areas and at dead-ends • Removing sediment that creates chlorine demand • Removing biofilm that converts inorganic to organic materials

  13. Coagulation to Remove TOC TOC Removal using Enhanced Coagulation for Surface Water Plants (TT) TOC Alkalinity (CaCO3) Mg C/L 0-60 60-120 >120 2.0 to 4.0 35% 25% 15% 4.0 to 8.0 45% 35% 25% >8.0 50% 40% 30% Florida Source Waters Typically Alum is used and requires sedimentation/filtration Lime can also be used but has less ability due to high pH

  14. Permanganate Long Used for Taste and Odor Removes color forming substances which are the same constituents that cause DBP formation Range of dosage vary on water quality with .25 mg/l to 20 mg/l. Average dosage is 2 to 4 mg/l with 30% TOC removal efficiencies reported Limitation is that can not be used in systems with High Sulfide Levels or with changing conditions Activated Carbon Filter With Source Water TOC from 2 to 4 mg C/L Activated Carbon Systems typically remove >50% Activated Carbon comes in two forms: Powdered Activated Carbon (PAC) Granular Activated Carbon (GAC) Removal mechanisms are the same Other Means to Remove TOC

  15. Factors Affecting Disinfection By-Product Production w/ Cl2 • Turbidity and the type of NOM present • Concentration of Chlorine added and how well it is mixed • Bromide Ion Concentration • Presence of H2S, Iron and NH3 • Age of Water System (amt of CI pipeline) • Warmer Temperatures • Longer Contact Times (MRT) • Presence of Sediment in Tanks

  16. Oxidation/Reduction Only DBPs Remain DBP Production Chloramines Breakpoint Chlorination Curve

  17. Steps in the Formation of DBPs with Free Chlorine • Inorganic reducing constituents such as H2S, Fe & Mn and NH3 compounds react first (oxidation reduction reaction). • When Iron, Sulfide or NH3 are present, they exert the major Chlorine Demand • Iron concentrations are required in the Secondary Standard submittal but Sulfide or NH3 are not. • If there are products of Biological Metabolism such as Nitrite this will also react. (Important in Nitrification) • Any readily soluble Organic Materials in the water (TOC) will then react forming DBPs. • Further Free Chlorine addition will not destroy DBPs. • Disinfection “jar test” can be used to identify reducing constituents but will not identify by specific constituent.

  18. Example of Calculating CL2 Demand * Note: Actual amount of oxidant must be about 15% – 20% higher

  19. DEP H2S Treatment Requirements

  20. DEP Iron Treatment Requirements • State Secondary Standards require Iron to be < 0.30 mg/l in the finished water • Thus water systems with iron concentration greater than 0.3 mg/l would need to install filters • Iron may be sequestered up to a concentration of 1.0 mg/l • In an aeration system Iron is removed by raising the pH while H2S is removed better at lower pH’s

  21. Sulfide is remove by lowering pH and filtering Unreacted Sulfide will form “blackwater” with unlined CI pipes Sulfate and Colloidal Sulfur can be reconverted to sulfide by bacteria in water tanks causing odor Iron is removed by raising pH and filtering source water Unfiltered Iron will result in “red water” complaints Iron can also be a corrosion product from unlined CI pipes Iron will result in staining Treatment Issues with Sulfide and Iron in Unlined CI Pipes > 0.3 mg/l Problematic because of colloidal solids

  22. Chlorine Disinfecting Power and pH Considerations in Water • Chlorine reacts with water • Producing hypochlorous acid (HOCl) and the hypochlorite ion (OCl-) • Chlorine is more reactive at lower pHs. • Low pH forms > HAA5s, High pH forms > TTHMs Old Hypochlorite contributes to DBP formation because doses must be higher! Hypochlorite (pH 12.5) raises pH at high dose levels! % HOCL % OCL- pH 6 7 8 9

  23. Chlorine Free Chlorine Improper NH3 application Poor Chemical Mixing Chloramine Breakdown Bromine Bromide from Saltwater or Brackish Water Intrusion Drought Conditions Presence of Free Chlorine Sources of Chlorine and Bromine in DBP Compounds

  24. Effect of the Addition of FreeCL at MCL+ Level with TOC Note that TTHM growth is directly proportional to the excess amount of chlorine present (in concentrations above 1 mg/l) and the excess TOC that is available for reaction. This relationship is steady as Cl residuals approach 1.5 mg/l. Note the 300% increase in the amount of TTHM made when chlorine and TOC are increased by 50%. CL at 4.3 PPM Florida Source Water often apporach 4 mg/l TOC

  25. Chlorine Detention Time Small System Ave Demand Time Paced Control Water Systems experience both Seasonal and Diurnal Demand Changes. Colder months require less chlorine dose. Wet and hot periods cause longer detention periods. In times when demand exceeds average demand, a time-paced Cl feed system overfeeds chlorine. Flow Paced Control

  26. Production of Total Trihalomethanes (TTHMs) • Trihalomethanes (TTHMS) are produced by the reaction of chlorine with organic constituents found in natural waters. • The 4 Trihalomethane compounds of concern are: Chloroform (typically >70% inland) Bromodichloromethane Bromoform (can be >70% coastal) Dibromochloromethane • The sum of the concentrations of these four compounds are Total Trihalomethanes (TTHMs) • However, Chloroform or Bromoform will always constitute the higher portion of the TTHMs. • Bromoform is produced in coastal areas due to brackish intrusion and varies by well. Bromoform is formed by the reaction of Cl on Bromide. • Chloroform is present in inland areas and varies by well.

  27. Where TTHMs are Formed • High Water Age (MRT) • Storage Tanks with poor water turnover • Low Demand Areas • Stagnant & Slow Moving Water Areas • Dead Ends Pipelines (MRT) • Note: Unlined CI Pipe (systems in existence before 1949) require higher residual chlorine levels Unlined CI Pipe Tuberculation with Bacterial Growth producing Organic Precursors

  28. Production of Haloacetic Acids • Like THMs, Haloacetic Acids are produced by the addition of free chlorine to waters containing natural organic materials. • These 5 compounds are regulated as HAA5s. Monochloroacetic Acid Monobromoacetic Acid Dichloroacetic Acid Dibromoacetic Acid Trichloroacetic Acid • These compounds will begin to degrade a few days after formation. • They can not be removed by air stripping.

  29. Where HAA5s are Found • Low Demand Areas • Toward Middle System Areas w/ high Chlorine concentration and low movement • Near High Chlorine Dose and/or Residual Locations • High Bacterial Growth internal to system • HAA5 will degrade in systems with high water age, thus highest HAA5s are not found at MRT

  30. Ratio of TTHM to HAA5 • Ratios of TTHM to HAA5 should remain relatively constant • Large variations indicate a change of system conditions • Since HAA5’s decay, an increase in HAA5 levels indicates that water age has declined • An increase in both would mean that Cl residuals are too high • Trending of changes can be very valuable for troubleshooting

  31. Chlorine Dose and Its Effect on DBP Production Typical Chlorine Doses may range between 2 mg/l to 4 mg/l with Chlorine Residual leaving the plant at an average near 1.5 mg/l. Often Chlorine Residual Concentration can be lowered proving significant reductions in DBP production.

  32. DBP Formation Potential Indicates Significance of DBP Problem Water Age After Watson and Montgomery AWWA Water Quality and Treatment, 1999 * TOX = Total Organic Halides

  33. Formation of DBP in a Typical Water Treatment and Distribution System ~ 50% Treatment ~ 50% Distribution

  34. Identifying the Point of DBP Production in a Water System • DBPs are equally produced in the treatment plant and in the WD system. • It is important to note where the DBPs are produced (extra sampling) to identify effective corrective actions. • Typically DBP problems occur at MRT Locations. • Proactive DBP Strategies should be targeted.

  35. Effects of Moving the Point ofDisinfection • Moving the Point of Disinfection acts in three ways: • Decreases significantly the time that the highest free chlorine concentration is in contact with organic material. • Treatment, especially coagulation, sed. and filtration removes a portion of the TOC. • In combining 1 & 2 above, the dose requirement for chlorine is lower and easier to predict Surface Water Process Treatment provides significant TOC reduction. However, any treatment process used provides some level of TOC reduction.

  36. Disinfection Location Action Benefit Chlorine Feed Reduce chlorine feed rates while maintaining proper chlorine residuals Fewer DBPs formed in the water system. No / little cost for this option. Chlorine Injection Point Change point of chlorine injection to reduce the age of chlorinated water Fewer DBPs formed in the water system. Small cost for this option. Chlorine Injection Boosters Add chlorine injection point(s) to boost Chlorine residuals in the distribution system instead of at the plant Lower total chlorine added at the plant site. Fewer DBPs formed in the distribution system. Alternate Disinfection / Application Use of chloramines in distribution systems with long detention times or selective use of preoxidation or oxidant such as NaMnO4 Fewer DBPs formed in the water system. Costs for this option could be significant. Effective Chlorination System Modification Strategies

  37. Water Age and DBP Production Other than Reducing Cl dose and residual levels, reducing water age is the most effective method available for reducing TTHM concentrations. There are two slopes present in TTHM development, The first is most significant and is related to Cl dose, the second is slower and related to Cl residual CL Residual CL dose Franchi and Hill, 2002

  38. Typical Distribution System Water Age (Days) AWWA: Water Age for Ave and Dead End Conditions

  39. Flushing Objectives Used in Water Distribution Systems Conventional Flushing < 2.5 fps velocity that reduces water age, raises disinfectant residual removes coloration & Unidirectional Flushing > 2.5 fps velocity that removes solid deposits and biofilm from pipelines

  40. Removing Sediment and Biofilm from Water Mains by Unidirectional Flushing • Sediment deposits and most biofilm can be removed if cleansing velocities can be achieved • The velocity that needs to be developed is 2.5 to 5 fps; these velocities will cause pressure drops and movement of sediment including rust to customer’s plumbing • To achieve these types of velocities without problems, a planned unidirectional approach must be used that valves off piping to force water to a certain location

  41. Effects of pH on the Production of DBPs in Distribution System TTHM and HAA% Formation Potential Note: HAA5 pH Franchi et al. 2002 Amy et al. 1987

  42. Problems with Water Turnover and Sediments in Tanks Increasing Bacterial Growth: 1. ) protection from UV, 2.) moderate high Temp., 3.) mildly alkaline pH (7.4 – 8.4) , 4.) O2 present and 5.) substrate for growth • Sediments contain significant concentrations of organic nutrients and exert a disinfectant demand leading to higher Cl doses • Sediments provide protective layers for biofilms which allow pathogens to repair • Sediments encourage the growth of slow growing nitrifying bacteria that lower Cl residual • Bacteria contribute organics that lead to the formation of DBPs • Bacterial growth lead to turbidity, taste and odor problems that require higher Cl dose Storage Tank Water Movement: 1.) Daily goal of 50% storage volume removed, 2.) Minimum of 20% - 30% , and Target of every 3 days

  43. Flushing Program Suggested Actions/DEP Rule Benefits to Treatment System Written Flushing Procedures Submit a Written Water Main Flushing Program. DEP Rule 62-555.350 Sampling is during normal operating conditions, and is not valid if you ONLY flush the day you are collecting samples Treatment Components in Contact With Water Clean & remove biogrowths, calcium or iron / manganese deposits, & sludge DEP Rule 62-555.350(2) Improves water quality, reduces chlorine demand & regrowth in the water system. Reservoirs and Storage Tanks Clean & remove biogrowths, Ca or Fe / Mn deposits, & sludge from storage tanks. DEP Rule 62-555.350(2) FAC Improves water quality, reduces chlorine demand & biological regrowth in the water system. Water Distribution Mains Begin systematic flushing of water system from treatment plant to system extremities. Improves water quality, reduces chlorine demand & biological regrowth in the water system. Dead-End Water Mains Flushing (every other day) or Automatic Flushing. DEP Rule 62-555.350(2) Improves water quality,& reduces biological regrowth. DEP Flushing Removal Requirements

  44. Use of Disinfectant Strategies • Reduce Dosing Concentration of Disinfectant • Change Points of Application • Change forms of Disinfectant • Use of Multiple Disinfectants • Change Disinfectant • Use of Orthophosphate in WD systems that use Unlined CI Pipe

  45. Advantages in the Use of Chloramine • Chloramines Not As Reactive With Organic Compounds so significantly less DBPs will form • Chloramine Residual are More Stable & Longer Lasting • Chloramines Provides Better Protection Against Bacterial Regrowth in Systems with Large Storage Tanks & Dead End Water Mains when Residuals are Maintained • Since Chloramines Do Not React With Organic Compounds; Less Taste & Odor Complaints • Chloramines Are Inexpensive • Chloramines Easy to Make

  46. Chloramine Disadvantages • Not As Strong As Other Disinfectants eg. Chlorine, Ozone, & Chlorine Dioxide • Cannot Oxidize Iron, Manganese, & Sulfides. • Sometimes Necessary to Periodically Convert to Free Chlorine for Biofilm Control in the Water Distribution System (Burn lasting 2 to 3 weeks) • Chloramine Less Effective at High pH • Forms of Chloramine such as Dichloramine cause Treatment & Operating Problems • Excess Ammonia Leads to Nitrification • Problems in Maintaining Residual in Dead Ends & Other Locations

  47. Nitrification Concerns in Water Storage Tanks with the Use of Chloramine • Nitrification is the conversion of ammonia to nitrite then to nitrate • Occurs in dark areas, at pH > 7, with at warm temperatures and long detention • Nitrification problems occur with systems that use chloramine which contains excess ammonia that when released can support the nitrification process • Nitrite (intermediate product) will consume free chlorine and chloramine disinfectants • Must ensure that disinfectant residual levels are adequate (> 1.5 ppm chloramine; with 2.0 to 2.5 recm.)

  48. Nitrification Monitoring Indicators • Higher Water Temperatures and • Depressed Disinfectant Levels • Elevated DBPs • Elevated Bacterial Counts (HPC)* • Elevated Nitrate/Nitrite Levels for Chloramination Systems • High Corrosion Potential • Direct Nitrification Monitoring ineffective * HPC use organic carbon as food, include total coliform; Not to exceed 500/ml in 95% of samples

  49. Troubleshooting DBPProblemsQuantitative Approach to DPB ReductionInteractive Portion of Presentation Bob’s Handouts

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