Monday, August 22, 2016

Disinfection By Products in Water

The use of chlorine, chloramines and ozone to disinfect drinking water has virtually eliminated the incidence of such waterborne diseases as typhoid, cholera, and dysentery in the United States. However, research has shown that chlorine and the other oxidizing disinfectants interact with natural organic matter present in rivers and streams and our drinking water supplies to form disinfection by-products (DBPs) that increase the incidence of cancer.

Although there are hundreds of disinfection by products that can form, the U.S. Environmental Protection Agency (EPA) only regulates 11 that were the most common when chlorine was the disinfectant of choice and were linked to health concerns. Some research done in the late 20th century indicated that certain byproducts of water disinfection are linked to increases in bladder cancer, liver, kidney, central nervous system problems, reproductive effects and linked to anemia. The EPA established maximum contaminant levels for these by products: four trihalomethanes (THMs), five haloacetic acids (HAAs), bromate, and chlorite in order to protect public health.

Strategies to control disinfectant breakdown products can be divided into three categories: Removal of disinfection byproduct precursors. Modification and optimization of the treatment and disinfection processes to limit the formation of these breakdown products. Removal of disinfectant breakdown products after formation using such filtering media as activated carbon. However, most water utilities changed their method of disinfection because it was the cheapest method to comply with EPA standards for the regulated disinfection by-products. This resulted in many water utilities moving away from chlorine disinfection to alternatives such as chloramine, chlorine dioxide, and ozone, and increased the adoption of chloramine because of its relatively lower cost. Chloramine is a combination of chlorine and ammonia.

After its introduction, it was discovered that chloramine can make drinking water more caustic that may cause an increased deterioration of old water pipes and degradation of valves and fittings. In water systems that still have lead containing pipes or components; this causes lead and other metals to leach into drinking water. This happened rather spectacularly in Washington DC in the late 1990’s. In addition, chloramine has its own breakdown products with potential health impacts.

Thought the federal government did not ban the use of lead pipes in new construction and repairs until 1986, many cities banned lead pipe use decades earlier out of health concerns. Most existing lead pipes are closer to 75-100 years old, are in the older cities of the east coast and mid-west and should have been replaced in the normal course of preventive maintenance program. Unfortunately, that is not how we operate in the United States. A few cities, including Madison, Wisconsin, and Lansing, Michigan, have taken steps to remove all of their lead pipes. Such projects can cost tens of millions of dollars and have to be paid for by either an increase in water bills, property owners or both. It was estimated by the American Water Association that there are 6.5 million lead pipes still in service in the United States while the EPA estimates that number at around 10 million. That does not even consider all the homes in America that have copper pipes with lead solder.

The 1994 amendments to the Clean Water Act Safe Drinking Water Act to regulate disinfection by-products formed when chlorine reacts with organic matter in drinking water resulted in elevated lead levels in the distribution system in Washington DC when they changed from chlorine to chloramine for disinfection. The treatment process for the Washington DC water supply was changed to add ammonia after primary disinfection to react with the remaining chlorine to prevent the formation of disinfection byproducts (haloacetic acids and trihalomethanes). The change caused a lowering of pH in the distribution system, the water became slightly more caustic than it had been, increasing the possibility of corrosion.

Shortly after the change, increasing pipe failures and levels of lead began appearing in the homes of Washington DC residents. The more caustic chloramine-treated water picked up lead from pipes and solder resulting in elevated levels and deterioration of the pipes. This is just one of the unintended consequences of the change to chloramine. Today, there are growing number of scientists who are warning that the unregulated disinfection by products from chloramine may be more problematic than the regulated ones. One of the disinfection by products of particular concern is Nitrogenous disinfection by products(N-DBPs). They are formed when nitrogen-containing compounds (fertilizers) react with certain oxidants/disinfectants especially in systems using chloramine. These N-DBPs include nitrosamines, nitriles, and hydrazine, and some of these compounds are one to two orders of magnitude more toxic than the currently regulated disinfection by products. We need to reexamine the approach we are taking for the ever increasing number of regulations with unintended consequences.

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