Why wouldnt the City just admit the Water tastes bad, smells bad, and doesnt make your stomach feel good when you drink it? Why not just be honest with the people of Willits? What does the Presidents Cancer Panel say about DBPs??? The Presidents Cancer Panel, a panel of 3 leading cancer specialists who advise the White House each year on the latest developments in cancer risk in the United States, just released their 2008-2009 report - and it contains statements that should make everyone in the water industry sit up and take notice. Cancer Panel ReportFor the first time, the panel has identified drinking water disinfection by-products as a significant environmental factor that contributes to cancer risk in the United States. We in the water industry are well-aware of the issue of disinfection by-products (DBPs), and the EPA and state regulators have established maximum safe levels for drinking water - no news there. But the elevation of this issue in the Presidents Cancer Panel may be a harbinger of increased public concern over an issue that, until now, has escaped notice. Are municipal water systems prepared for this increase in public concern? What options are available to deal with DBPs? We know that DBPs are formed when naturally occurring organic matter reacts with disinfectant. One set of options involve reducing the amount of organic carbon in the source water - but this requires complicated upgrades to treatment plants in the form of enhanced coagulation and sedimentation. Another approach is to switch primary disinfection treatment technique to ultraviolet (UV) treatment or ozone which disinfects without producing DBPs at the plant, also involving major retrofits at a significant cost. It used to be thought that the switch from chlorine to chloramines would solve the DBP issue for most municipalities. Chloramines are a less powerful disinfectant, but they do not produce tri-halo methanes or halo-acetic acids when they interact with organic carbon in water. Recent evidence has shown that new (unregulated) DBPs are formed when chloramines react with organic carbon - and some of these may pose an even larger health concern than the compounds we monitor today. The other approach to lower DBP levels would be to lower the amount of disinfectant in the distribution system. But most operators resist this approach because it lowers the level of protection against pathogens. Furthermore, in many distribution systems, disinfectant is used up as the water travels through the distribution system - minimum levels of disinfectant must still be present when the water reaches the customer. But why is so much disinfectant being lost in the distribution system? One reason is poor mixing in storage tanks. When a tank is unmixed, it loses disinfectant residual at the top first. This is because the top water heats up and stratifies (increasing the rate of disinfectant evaporation) and because biofilms readily form on the walls of the tank near the water surface. These biofilms add new organic carbon which reacts with the remaining disinfectant, lowering the residual and increasing the production of DBPs. In contrast, a well-mixed tank has a much lower disinfectant residual demandbecause the disinfectant residual is circulated to all parts of the tank, keeping biofilms along the walls of the tank at bay. Without the biofilms, the overall residual demand is less. We have many examples of municipalities that have installed the PAX Water Mixer and lowered the amount of on-site dosing by up to 90%. One municipality installed PAX mixers in all their tanks and was able to lower the amount of disinfectant leaving their treatment plant by 30% - while still maintaining great residual levels for the customer. By lowering the residual demand in tanks, active mixers can allow municipalities to lower their use of disinfectant in general, leading the lower levels of DBPs as a result. For DBP control, active mixing is an economical approach to an otherwise expensive problem. From page 55 of the Presidents Cancer Panel 2008-2009 report: The Federal standard for disinfection by-products in public water supplies is 80 parts per billion of THM as an annual average.268 THMs are measured because they generally reflect levels of other chemicals in DBP mixtures. If not controlled, DBPs in water systems can range up to several hundred parts per billion. In addition, a recent study 269 suggests that THM levels vary within a water system, with the highest levels found in water that stays in the system the longest after disinfection. In this study, rectal (bromoform THM only) and bladder cancer risks were highest among those who consumed the greatest amount of water at points within the distribution system with the oldest post-disinfection tap water. paxwater/pax-water-blog/bid/40289/President-s-Cancer-Panel-Drinking-Water-DBPs-Pose-Significant-Risk
Posted on: Fri, 08 Nov 2013 20:45:18 +0000
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