2008 newwa annual conference in burlington vt chloramine talk


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  • Chloramines reduce DBP risk : The primary benefit a utility will receive when switching from free chlorine to chloramines is a dramatic reduction in DBP formation. Chloramines simply don’t react with natural organics to form DBPs as readily as free chlorine. In Manchester, NH, TTHMs have dropped form the 60-80 ug/L range to about 5 or 6. HAAs have also dropped into the single digits. Chloramines are less powerful and slower acting than free chlorine, but can be more effective at penetrating and inactivating biofilms in the distribution system. Chloramines will change water quality conditions in the distribution system, for example: excess free ammonia is food for nitrifying bacteria. This may result from a low Cl2:NH3 ratio or simply the natural decay of the chloramine residual over time. Chloramines can reduce ORP which can have a profound impact on corrosion chemistry…We’ll take a close look at the Washington DC story that erupted in early 2004 to illustrate this and we’ll see that changing to chloramines alone DOES NOT directly cause corrosion problems. The final take home message is that a decision to switch to chloramines requires careful planning over several months to a year (or perhaps more), it should be accomplished by a team of experienced professionals, involve lots of public notification, and a comprehensive water quality monitoring plan following the switch to avoid potential problems.
  • Before we get to the Washington DC nightmare, let’s quickly review some basic chloramine chemistry The goal is to form a monochloramine residual by adding chlorine and ammonia at a carefully controlled and monitored ratio We need to understand how pH impacts the predominance of chloramine species We also need an understanding of conditions that may lead to nitrification in the distribution system and how to interpret system water quality data to avoid or mitigate the problem And finally, understanding the chemistry will help us understand what happened in Washington, DC
  • Adding ammonia to water containing free chlorine results in the formation of chloramine species. The species formed is primarily a function of the chlorine to ammonia ratio and pH. Temperature and the presence of other compounds are also factors. The equations for the three chloramine species are listed here Monochloramine is desired because it is a more powerful disinfectant than di- and tri-chloramine and it is more stable and has much less detectable taste and odor in water Keeping the chlorine to ammonia ratio between 3 and 5:1 at a pH above 7.5 favors the formation of the desirable monochloramine species As the ratio increases beyond 5:1, the formation of undesirable di- and tri-chloramine species predominates
  • Here is The Famous Breakpoint Curve The Y-axis shows the measured chlorine residual and the X-axis is the chlorine dose. Both in mg Cl2 / mg NH4-N As the chlorine dose increases from 0 to 7 mg Cl2 per 1 mg ammonia monochloramine is the predominant species present, with some dichloramine formation between 5 and 7. This plot illustrates nicely that keeping the chlorine to ammonia ratio between 3 and 5:1 forms almost exclusively the desired monochloramine residual and does so at levels that are detectable and will persist in the distribution system As the ratio goes beyond 5:1, undesirable dichloramine begins to form, AND the measured residual begins to drop until it is completely lost somewhere between 7 & 8. This phenomena is referred to as the “breakpoint” where all of the mono and dichloramine has been oxidized. As the chlorine dose and corresponding ratio increases further, trichloramine and free chlorine predominate and the phone begins to ring with lots of taste and odor complaints! Chlorine and ammonia react very quickly together, so if either or both are poorly mixed in the treatment process the actual applied ratio can vary dramatically from what is intended. The bottom line: good mixing and monitoring is crucial
  • Here are two graphs showing the impact of pH on chloramine species formation The graph on the left shows percentage of combined chlorine as a function of pH. Following the dashed green line clearly illustrates that monochloramine formation is favored over di- & trichloramine at a pH’s beyond 7…and maintaining the pH between 8 and 8.5 is a common practice for plants practicing chloramination The graph on the right illustrates that the rate of monochloramine formation is also a function of pH…and that the rate peaks at a pH of 8.4
  • Adding ammonia, a source of nitrogen, to water can potentially lead to nitrification. Nitrification can occur if excess ammonia is available in the system. This will happen if the chlorine to ammonia ratio is too low or simply through autodecomposition of the monochloramine residual over time, especially in warm water conditions. Two groups of nitrifying bacteria are responsible for nitrification nitrosomonas feed on the excess available nitrogen oxidizing it to nitrite. Nitrobacter in turn feed on nitrite converting it to nitrate The factors that impact nitrification potential are The amount of free ammonia as nitrogen available Water temperature pH (the rate is highest at pH 7.5 to 8.5) And residence time
  • Nitrification can lead to: Loss of disinfectant residual can lead to an increase in HPCs and total coliform bacteria levels Nitrifying bacteria consume dissolved oxygen as they convert ammonia to nitrite and nitrate Consumption of alkalinity can reduce the buffering capacity of the water, lower the pH and make the water less pH stable Corrosion potential can be increased due to a lower oxidation-reduction potential (ORP) and/or lower pH…the Washington, DC story will focus more on this impact. Nitrifying bacteria will cause nitrite and nitrate levels to increase Taste and odor complaints may increase
  • To control nitrification you have to monitor your system very carefully: increases total coliforms, HPCs, nitrite and nitrate levels, and loss of residual are key indicators. Knowing your system and understanding where the greatest potential may exist (storage tank, dead ends, places where water age is an issue) will help to control nitrification. If nitrification occurs, or to pre-empt it from occurring, some utilities convert to free chlorine residual for short periods. Be warned that doing so will likely create taste and odor problems due to shifting chlorine to ammonia ratios and localized production of di- & trichloramine Spot chlorination of water tanks and/or other parts of your system where water age is a concern may help Increasing chloramine residual, particularly in warmer months will help Increasing the chlorine to ammonia ratio closer to 5:1 will reduce free ammonia levels in the system…minimizing the food source for nitrifying bacteria Controlling the distribution system pH at 8.4 promotes optimum monochloramine formation System flushing and water age reduction strategies will also help considerably
  • LCR compliance monitoring began to show levels in the system above the 90 percentile 15ppb action level beginning in July 2000. The number of homes exceeding the action level grew rapidly in each of the next several LCR monitoring cycles until in February, 2004 when the Washington Post ran the story “The Lead Hits the Fan”. The next month two congressional hearings focused on WASA’s lead problem and EPA offered some heavy criticism leading to the resignation of the WASA Director.
  • DC’s lead problem was the most intensely covered national drinking water story in recent years. In 2004 & 2005 More than 230 articles appeared in the Washington Post More than 120 stories on local TV and radio Corrosion experts were consulted In April 2004 the senate introduced the Lead-Free Drinking Water Act and WASA ships 23,000 filters to homes with lead service lines In May the Post and Time Magazine decree that chloramine is the smoking gun and cause of the lead problem
  • WASA, USEPA, and a Technical Expert Work Group conducted a series of studies to address, reduce, and control lead levels at the consumer tap. In June 2004, WASA began zinc-free orthophosphate addition in a portion of their system and based on the favorable results, began full system application in August. So finally, after about four years of increasing lead levels, and lots of public scrutiny and outrage, the levels began to drop To add insult to injury, right about that time, the legal system began a massive class action lawsuit advertising campaign
  • The problem in Washington, DC gave chloramines a severe black eye and their use continues to be questioned by some citizens and groups as the folks from right here in Burlington, VT can attest – for reasons other than corrosion. Chloramine use continues to grow today to enable utilities to comply with more stringent DBP Rules The big lesson learned from the Washington experience is that careful evaluation and attention must be devoted to corrosion issues when changing water quality in the distribution system.
  • The Washington experience raised many questions in the effort to determine what really happened. Were things done incorrectly and could this happen in New England? Absolutely. Did the switch to chloramines cause the problem? Yes, but it could have been avoided. Were chloramines the primary cause? No! Do we fully understand the science, the chemistry? For the most part yes. Is chloramine disinfection safe? When it use is carefully planned and monitored…yes.
  • Reviewing the history of what happened in Washington reveals a troubling, but not that surprising or uncommon set of circumstances. For decades, lead service line replacement had been debated and recommended but the price tag was too high. There are over 28,000 identified lead service lines in this densely populated city. Corrosion control issues had been raised over the same time period with little being done to address these concerns. Almost immediately following the switch to chloramines in 2000, lead and copper corrosion problems began to appear in the form of pinhole leaks in copper services and elevated lead levels at consumer taps. Chloramines altered the corrosion chemistry and accelerated lead leeching from service lines. The already dubious corrosion control strategies and history of lead risk were pushed to the brink and, as they say, all hell broke loose! The consequences and public outcry were devastating not just for Washington, DC, but for all of us in the water business.
  • Looking back at chloramine chemistry again, two important differences are noted between chlorine (HOCl) and monochloramine reactions and their impact on corrosion: Free chlorine is a much more powerful oxidizer and will establish a higher ORP in the distribution system than monochloramine. As I described earlier, monochloramine adds a nitrogen source that can, through the nitrification process, further lower the ORP and the pH in some cases. ORP and pH play a crucial role in lead and copper corrosion chemistry
  • Another look at nitrification’s impacts: Nitrification, as described earlier, is the conversion of ammonia to nitrate by nitrifying bacteria under aerobic conditions. The reaction impacts corrosion chemistry because
  • 2008 newwa annual conference in burlington vt chloramine talk

    1. 1. The Use of Chloramines as a Secondary Disinfectant: Is Your Chemistry Good Enough? David G. Miller, P.E. Water Supply Engineer Manchester, NH Water WorksVoice: (603) 624-6842 E-mail: dmiller@manchesternh.gov and James P. Malley, Jr., Ph.D. Professor of Civil/Environmental Engineering University of New Hampshire (UNH) Voice: (603) 862-1449 E-mail: jim.malley@unh.edu NEWWA 127th Annual Conference September 14-17, 2008 Burlington, VT
    2. 2. Acknowledgements• NEWWA Disinfection Committee• Manchester, NH Water Works• UNH - Environmental Research Group• U.S. Army Corp. of Engineers• Information presented by WASA• Information presented by WSSC• USEPA Reports• Phillippe Boissonneault, Portland Water District• Cynthia Klevens, NHDES• Professor Gregory Harrington, University of Wisconsin – Madison
    3. 3. Take Home Messages• Chloramines Reduce DBP Risks to Public Health• Chloramines Reduce Microbial Regrowth and Risk in Distribution Systems and in Hospitals• Chloramines WILL Change the Water Quality Conditions in a Distribution System (especially the ORP)• Chloramines alone DO NOT cause Corrosion Problems• The Decision to Switch to Chloramines Requires: – An Experienced Team Effort – Careful Planning Including Public Education – Careful Implementation of Switching to Chloramines – System Monitoring of Key Water Quality Parameters {e.g., pH; Cl2 to NH4-N Mass Ratio; Lead and Copper; Microbes, Ammonia, Nitrite and Nitrate} is Needed
    4. 4. Outline• Chloramine Chemistry Basics – We want to form Monochloramine (NH2Cl) – Importance of the Chlorine to Ammonia- Nitrogen Mass Ratio – Importance of pH Effects on Chloramine Species – Issues with Nitrification• Chloramines and Lead in Washington, D.C. The Chemistry Explains/Solves the Problem
    5. 5. Chloramine Formation Equations • Monochloramine (NH2Cl): HOCl + NH3 → NH2Cl + H2O • Dichloramine (NHCl2): HOCl + NH2Cl → NHCl2 + H2O • Trichloramine (NCl3): HOCl + NHCl2 → NCl3 + H2O • Organochloramines: HOCl + Organic Amines → Organochloramines + H2O============================================We select for Monochloramine since it is a strongerDisinfectant, is more stable and has less taste and odor issuespH and Cl2 to NH4 -N mass ratio are the key factors to control
    6. 6. The Famous Breakpoint Curve 8Chlorine Residual mg Cl/mg NH-N 6 4 NHCl2 4 HOCl + OCl- 2 2 NH2Cl NCl3 0 0 2 4 6 8 10 12 14 16 Chlorine Dose, mg Cl2/mg NH4-N Target Ratio in Practice is 3:1 to 5:1 mg Cl2 / mg NH4-NBE CAREFUL! In practice, poor blending/mixing can cause ratios as high as 12:1 which will have negative impacts
    7. 7. 100 80 MonochloramineTotal Combined Chlorine (%) 60 40 20 Dichloramine Nitrogen Trichloride 3 5 6 7 8 pHpH 8.3 to 8.4 is commonlyused as the optimum target for monochloramineformation at a Cl2:NH4 -N mass ratio of 3:1 – 5:1
    8. 8. Potential for Nitrification• When the Cl2:NH4-N mass ratio is too low or for some other reason excess levels of NH4-N persist in the distribution system, there is strong potential for nitrification events especially in warmer water• Nitrification – the two step microbial conversion of ammonia to nitrite and then to nitrate NH3 Nitrosomonas NO2 Nitrobacter NO3• Factors that Effect the Potential: – Free NH4-N Concentration – Temperature – pH range – 7.5 to 8.5 is where it occurs fastest
    9. 9. Impacts of Nitrification• Degrades chloramine residual• Consumes dissolved oxygen• Consumes alkalinity• Can increase potential for corrosion either due to lower ORP (REDOX) potential in the system and/or lower pH• Increases HPC counts and can indirectly lead to coliform rule violations• Increases nitrite and nitrate levels• Can result in taste and odor complaints
    10. 10. Control of Nitrification• Increase Monitoring of HPCs, Nitrite and Nitrate to Understand Where and Why it is Occurring• Conversion to Free Chlorine For Short Periods – {often termed a chlorine burn}• Spot Chlorination “Tea-Bagging” of Water Towers• Increase Chloramine Residual• Increase Chlorine to Ammonia Nitrogen Mass Ratio• Set pH for Optimum Monochloramine Formation• Increase Flushing especially for dead ends• Reduce Water Age
    11. 11. The Washington, D.C. Case StudyHistoryWater Source is the Potomac RiverThe U.S. Army Corp. of Engineers – Washington Aqueduct Operates Reservoirs and Two Conventional Treatment Plants: Dalecarlia and McMillan Producing about 180 MGD Total The treatment plants use chlorine for disinfection and in November 2000 switched to Chloramines in the distribution system to control DBPs for lead and copper rule compliance the plants add Lime to maintain a positive Langelier Index and favorable Stability IndexWashington Water and Sewer Authority (WASA) – Provides water to 130,000 Service Connections (23,000 Lead Services) in the 8 Wards of Washington, D.C. - 725 Square Miles and 1,300 miles of piping.
    12. 12. Lead Problems in Washington, D.C. Fall 2001 – Spring 2003 53 Homes Exceed 0.015 mg/L (Lead Levels Up to 0.600 mg/L Documented) Spring 2002 to October 2003 5000 Homes Exceed Lead Limit February 2, 2004 Washington Post Article Exposes the Lead Problem – “The Lead Hits the Fan” A Media Feeding Frenzy Results March 2004 Two Congressional Hearings; USEPA CriticizesMap of Lead services in DCWASA
    13. 13. Lead Problems in Washington, D.C. March 2004 WASA Convenes Panel of Corrosion Experts April 7, Senators introduce the Lead-Free Drinking Water Act of 2004, S. 2733 April 8, WASA Completes the Shipment of 23,000 Filters to Homes with Lead Service Lines May 2004 Washington Post and Times Magazine Articles Decree that Chloramines are Cause of the Lead Problem Noting Switch Back to Chlorine as Problem Solution Between April 2 andMap of Major Lead Levels in DCWASA May 8, 2004
    14. 14. Lead Problems in Washington, D.C. June 2004 Washington Aqueduct Begins Pilot Test of Orthophosphate (Zinc Free) July 17, WASA and USEPA Enter a Multiphase Agreement to Address the Lead Problem August 23, Washington Aqueduct Begins Feeding Orthophosphate (Zinc Free) System Wide September 2004, Lead Levels Continuing to Drop, Class Actions Lawsuits Beginning and Legal Websites PoppingMap of Lead Service Replacements in DCWASA Up All Over The Area
    15. 15. Lead Problems in Washington, D.C. 2004 to 2006, chloramines were given a black eye and their use has been questioned by some citizens and groups Present Day - we have learned from the Washington, D.C. case and have paid close attention to corrosion issues when changing distribution system water quality Present Day – chloramine use continues to grow but carefully and with increased attention to potential forMap of Lead Service Replacements in DCWASA corrosion issues
    16. 16. What Happened in Washington, D.C. ? Were Things Done Incorrectly ? - YesCould this happen to a New England Water Utility ? - YesDid the Switch to Chloramines Cause the Problem ? - Yes Were Chloramines the Primary Cause ? – No Do We Understand the Science ? - Mostly Yes Can Chloramines Be Used Safely ? - Yes
    17. 17. What Happened in Washington, D.C. ?• For over 20 years, Lead Service Line Replacement has been recommended in D.C. – its costs prevented it• For over 20 years, Corrosion Control Issues have been raised in D.C. – little was done except Lime addition• After switching to Chloramines in 2000, Corrosion problems were noted almost immediately especially in the form of pinhole leaks in copper services both at WASA and at its neighbor WSSC. WASA lead monitoring results in early 2001 showed increasing lead levels• Chloramines changed the water chemistry resulting in higher lead leaching primarily from lead service lines and to a smaller degree from in-line brass fixtures - this put a system with a history of corrosion issues and lead risk over the top – with serious public consequences for us all
    18. 18. The Chloramine Chemistry Involved• As we noted earlier, chloramine use normally depends on the formation of monochloramine as follows: HOCl + NH3  NH2Cl + H2O Two important differences between chlorine (HOCl) and monochloramine (NH2Cl) of importance to corrosion are:• Chlorine is a much stronger oxidizing agent and will insure more oxidizing conditions (higher ORP) in the distribution system than monochloramine• Monochloramine introduces amines or ammonia into the distribution system and this nitrogen source can result in Nitrification which can further lower the ORP and in some systems lower the pH (this has been well proven in distribution systems especially those which have a long retention time and are in warmer climates).
    19. 19. Nitrification’s Impacts• Nitrification is the conversion of ammonia to nitrate by naturally occurring microorganisms under aerobic conditions. It follows the general reaction: NH3 + 2 O2 + Nitrifying Microbes  NO3- + H+ + H2OThis reaction causes two very significant problems for corrosion control in distribution systems:• It consumes oxygen making for more reducing conditions in the distribution system which leads to greater metals (lead and copper) solubility/leaching.• It produces acid (H+) lowering the pH or at least the buffering of the system which also leads to greater metals leaching (not a major factor in Washington, D.C.)• In the Washington D.C. case the water buffering was adequate to prevent any lowering of pH
    20. 20. Review of Lead Chemistry2Pb(s) + O2 (g)  2PbO(s) Lead Oxide2PbO(s) + 2HOCl  2PbO2(s) + 2H+ + 2Cl –2PbO2(s) Lead DioxideLead dioxide is a critical intermediate in the leaching of leadand is very subject to water quality changesEffect of Lowering pH 2PbO2(s) + 4H+  2Pb++ + 2H2OEffect of Removing Oxygen – A Reducing EnvironmentNH3 + 2O2 + Nitrifying Microbes  NO3- + H+ + H2O2PbO2(s)  2Pb++ + 2O2 + 4e -======================================================== ++ - + -
    21. 21. B (0.008 mg/L) (0.045 mg/L) C N(0.600 mg/L) Chemical Equilibrium of Lead Levels B – Before Change to Chloramines C – After Change to Chloramines N – Effects if Nitrification Occurs and Lowers pH and ORP
    22. 22. Steps to Resolve the Problem (1/3)• Switch Back to Free Chlorine – Would help insure the PbO2 (s) Form Dominated So the Lead Levels in the DS Would Drop – Would eliminate the reducing environment and prevent Nitrification – Return to the Health Risk Concerns of High DBPs at the Consumer’s Tap – Return to the Health Risk Concerns of Regrowth in the DS and No Residual Disinfectant Protection
    23. 23. Steps to Resolve the Problem (2/3)• Remove the Sources of Lead – Replace the Lead Service Lines – Impose Tougher Standards for “Lead Free” Brass (currently allow 8% lead by weight) – This is a costly effort and will take years to accomplish (it has begun in many Water Systems and will eventually be accomplished) – It may be impossible to identify and remove all sources of lead from the DS plumbing
    24. 24. Steps to Resolve the Problem (3/3)• Apply A Different Corrosion Control Strategy and Keep Chloramines – Improve Distribution System Flushing and Maintenance Procedures – Use an Extended Free Chlorine Residual Flush or Do Twice per Year (to prevent Nitrification) – Switch to an Orthophosphate Corrosion Inhibitor and Work to Optimize System-wide pH Control – Increase monitoring and data analysis and then communication between all parties
    25. 25. Orthophosphate for Corrosion ControlOrthophosphate – Food grade phosphoric acid H3PO4;Trisodium orthophosphate Na3(PO4); and Zincorthophosphate Zn3(PO4)2 are all used by water utilities tocontrol corrosion. The later two are not used if Sodium is anissue (e.g., in MA) or if Zinc becomes a wastewatertreatment issue as in the case of WASA. Typically 3 ppm isadded at first and then the dose is optimized often to the 0.5to 2 ppm range The phosphate ion can then react with thepipe (metal) material that is corroding to form a protectivephosphate solid coating ( Pb3(PO4)2(s) ): 2H3PO4 +  6H+ + 2PO43 – 3PbO2(s) + 6H+  3Pb++ + 3H2O ==================================
    26. 26. Corrosion Control is Complex• Much success with corrosion control has been achieved in drinking water and much has been learned by researchers but there are cases where the chemistry of the water and the distribution system are complex and corrosion control strategies are unsuccessful.• Careful control of pH and system ORP is very important as is careful selection and application of corrosion control chemicals. Good monitoring is vital• A thorough understanding other factors such as water treatment plant processes; nature and role of organic matter (TOC) in the system; electrochemical aspects such as mixing of pipe materials; electrical grounding; and biofilm aspects may all be important
    27. 27. DC WASA Pledge in USEPA AgreementTwelve Point Plan of What WASA is Actually Implementing:• Significantly accelerate the replacement of all District public space lead service lines compared to EPA’s requirements.• Work in partnership with a local financial institution to create a means tested loan program to help customers finance the replacement of lead service line pipes on private property.• Continue to work with District government agencies to identify public grant funds to help District residents with lead service line pipe replacements.• Appoint a Lead Service Coordinator reporting directly to the General Manager to manage all day-to-day WASA activities regarding lead service line replacements, community outreach, communications and water testing.• Launch a Mobile Community Response Unit to more readily address customers concerns.• Work closely with WASA stakeholders, including elected officials, faith-based, community and civic organizations, and others to ensure communications are clear and reach audiences appropriately, including those that don’t speak English.
    28. 28. DC WASA Pledge in USEPA Agreement Twelve Point Plan (continued):• Measure communication effectiveness in a quantitative manner.• Strengthen its partnership with the D.C. Department of Health to address any health concerns of D.C. residents regarding lead leeching.• Work closer with the Washington Aqueduct regarding production of water provided to D.C. residents. System-wide Orthophosphate Now in Use• Further develop corporate partnerships to benefit resident and rate payers which will specifically address the further distribution of water filters and the availability of bank loans to residents in order to finance lead service line replacements on private residential property.• Work with the D.C. Department of Health and experts from the George Washington University School of Public Health to more fully understand and communicate to residents information now available from local research and analysis regarding the health effects of water-based lead exposure.• Convene a National Water Authority Peer Group Workshop so experts, scientists and health professionals can discuss and explore the D.C. experience with other utilities in an effort to better frame future policy discussions for the nation and our policymakers.
    29. 29. Take Home Messages• Chloramines Reduce DBP Risks to Public Health• Chloramines Reduce Microbial Regrowth and Risk in Distribution Systems and in Hospitals• Chloramines WILL Change the Water Quality Conditions in a Distribution System (especially the ORP)• Chloramines alone DO NOT cause Corrosion Problems• The Decision to Switch to Chloramines Requires: – An Experienced Team Effort – Careful Planning Including Public Education – Careful Implementation of Switching to Chloramines – System Monitoring of Key Water Quality Parameters {e.g., pH; Cl2 to NH4-N Mass Ratio; Lead and Copper; Microbes, Ammonia, Nitrite and Nitrate} is Needed
    30. 30. The Use of Chloramines as a Secondary Disinfectant: Is Your Chemistry Good Enough? David G. Miller, P.E. Water Supply Engineer Manchester, NH Water Works Voice: (603) 624-6842 E-mail: dmiller@manchesternh.gov and James P. Malley, Jr., Ph.D. Professor of Civil/Environmental Engineering University of New Hampshire (UNH) Voice: (603) 862-1449 E-mail: jim.malley@unh.edu TI O NS! FO RQ UEST IME