Disinfection Byproducts in the Drinking Water What Does it Mean and What is Being Done

Transcription

1 Disinfection Byproducts in the Drinking Water What Does it Mean and What is Being Done

2 Existing Water System

3 What Are Disinfection Byproducts (DBPs)? DBPs are formed when disinfectants used in water treatment plants react with bromide and/or natural organic matter (i.e., decaying vegetation) present in the source water. Disinfection byproducts for which regulations have been established include trihalomethanes, haloacetic acids, bromate, and chlorite.

4 Why Chlorinate Drinking Water? Drinking water is disinfected to kill bacteria, viruses, and other organisms that cause serious illnesses and deaths. Disinfection of drinking water has benefited public health enormously by lowering the rates of infectious diseases (for example, typhoid, hepatitis and cholera) spread through untreated water. Chlorine is the most commonly used disinfectant.

5 Trihalomethanes (THMs) Trihalomethanes are one group of chemicals that are formed when chlorine or other disinfectants used to control microbial contaminants in drinking water react with naturally occurring organic and inorganic matter in water. The trihalomethanes are chloroform, bromodichloromethane, dibromochloromethane, and bromoform.

6 Haloacetic Acids (HAA5s) Haloacetic Acids are another group of chemicals that are formed when chlorine or other disinfectants used to control microbial contaminants in drinking water react with naturally occurring organic and inorganic matter in water. The regulated haloacetic acids are: monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, and dibromoacetic acid.

7 DBP Regulations The Environmental Protection Agency (EPA) began regulating DBPs in drinking water in At that time, the maximum contaminant level (MCL) for THMs was set at 100 parts per billion (ppb). There was no limit set for HAA5s. In 1998, the EPA issued the Stage 1 Disinfectants and Disinfection Byproducts Rule (Stage 1 DBPR), which established the MCL for THMs at 80 ppb and for the first time set an MCL for HAA5s at 60 ppb. These standards had to be met by the end of 2002 for large surface water systems, and by the end of 2004 for all other systems.

8 DBP Regulations Continued Stage 1 DBP compliance was based on annual running averages for all sample locations within the water system. The Stage 2 DBPR was finalized in December of Under this rule, system conducted evaluations of their distribution systems to identify locations with high DBP concentrations. These locations will be used as sampling sites for Stage 2 DBPR compliance monitoring. Stage 2 compliance will be based on running annual averages at each individual sample location.

9 Round Lake DBP Results DATE HAA'S (ug/l) 12 MONTH RUNNING AVERAGE MCL (ug/l) TOTAL THM'S (ug/l) 12 MONTH RUNNING AVERAGE 8/2/ /11/ /2/ /3/ /12/ /6/ /9/ /13/ /19/ MCL (ug/l)

10 Factors Affecting DBP Formation Natural organic matter (NOM), which is generally measured as total organic carbon (TOC). Bromide Temperature Disinfectant dose Contact time with the disinfectant

11 Natural Organic Matter NOM is a complex mixture of compounds formed as a result of the breakdown of animal and plant material in the environment Found primarily in surface water sources that are exposed to the environment Amount of NOM in source water can change seasonally or as a result of a significant weather events

12 Temperature and ph THM formation increases with increasing ph, but ph has a mixed effect on HAA formation DBP formation increases with increasing temperatures Higher water temperatures also create a higher chlorine demand, which causes a need to increase chlorine dosages

13 Chlorine Dosage and Contact Time DBP formation is greatly affected by the amount of chlorine in the water and the amount of time the water resides in the water system once chlorine is added THMs form over time and continue to increase in the presence of chlorine. HAA5s increase over time and form more rapidly, but can reach a point where they peak and start to decrease

14 Public Notification

15 DBP Health Effects Since the discovery of chlorination byproducts in 1974, numerous studies of the health effects from exposure to high dosages of these contaminants in laboratory animals have been conducted. These studies have shown several DBPs to be carcinogenic, and some have also been shown to cause adverse reproductive or developmental effects in laboratory animals. However, there is considerable uncertainty involved in using the results of high-dose toxicological studies to estimate the risk to humans from chronic exposure to low doses of these and other byproducts.

16 SCWA Treatment Techniques The Saratoga County Water Authority operates a 14 MGD treatment plant in the Town of Moreau, which treats water from the Upper Hudson River. This plant has been in service since February of 2010 The treatment process includes the addition of coagulant, sodium permanganate and powder activated carbon to the source water, and filtration through 0.1 micron membrane filters. Caustic soda is added for corrosion control and ph adjustment, and sodium hypochlorite (chlorine) is added for disinfection

17 SCWA Distribution System The SCWA delivers its finished water through a 27 mile long 30-inch transmission main that terminates at the Luther Forest Technology Campus. Purchasing systems include the Clifton Park Water Authority, the Towns of Ballston and Wilton, and the Village of Stillwater. The Town of Stillwater purchases water from the Village of Stillwater, and the Village of Round Lake purchases water from the CPWA.

18 CPWA Connections to SCWA System

19 Treatment Challenges There are a number of elements that are affecting the formation of DBPs in not only the SCWA system, but in the purchasing systems as well. Long travel times in the SCWA transmission main allow for excessive contact time between the NOM in the water and chlorine. These travel times will decrease once Global Foundries is fully operational and purchasing its anticipated amounts of water.

20 Treatment Challenges Cont d Seasonal changes in the makeup of natural organic matter in the source water have caused taste and odor issues for the SCWA in the past. A change in treatment from powder activated carbon to sodium permanganate seemed to alleviate the taste and odor issues this past fall, but did not have a positive effect on DBP reductions. Further aging of water within the purchasing systems causes further development of DBPs within those systems, so a less than desirable situation becomes worse.

21 What is Being Done? In late 2011/early 2012 the SCWA did some intensive flushing of their transmission main. Although hundreds of millions of gallons of treated water was run to waste, the SCWA was able to consistently increase its usage for a period to better assess the effects of reduced water age on DBP formations. DBP results were noticeably improved during this time. The SCWA also made modifications to its treatment process by adjusting coagulant and disinfectant dosages and eliminating the prechlorination process that allowed chlorine to react with organic matter before filtration.

22 What is Being Done? (Cont d) In the fall of 2012, the SCWA began feeding sodium permanganate in place of powder activated carbon to mitigate taste and odor issues. It was also expected that it would reduce DBP formation, although early results have not shown it to be as helpful as anticipated. In December 2012, the SCWA resumed the addition of powder activated carbon to its treatment process. SCWA is currently working to assess the effects of the simultaneous addition of sodium permanganate and powder activated carbon on DBP formation.

23 What is Being Done? (Cont d) Work is underway at SCWA to further reduce the amount of DBP precursors in the raw water stream by installing infrastructure to eliminate the recirculation of backwash water through the treatment process. The SCWA has formed a technical advisory committee made up of members from each water system receiving water directly or indirectly from the SCWA. The committee will meet regularly to discuss sampling, sample results and methods of further reducing DBPs throughout the distribution area, as well as any other water-related issues affecting the group.

24 What Can You Do? Point-of-use carbon filters are readily available and are effective at removing DBPs and other contaminants from drinking water.