NDMA, Chlorate, and the 6 Year Review - Managing Risks in Light of Potential Changes to Stage 2 DBP
- Meric Selbes, Ben Stanford, Allison Reinert - Hazen and Sawyer
- Tanju Karanfil - Clemson University
Disinfection by-products (DBPs) are formed as a result of the reactions between organic matter present in water and oxidants such as ozone, chlorine dioxide, and chlorine used during drinking water treatment. The US Environmental Protection Agency (USEPA) has regulated total bromate, chlorite, trihalomethanes (THMs) and five haloacetic acids (HAAs). However, research has shown that unregulated DBPs (such as nitrogenous DBPs) exhibit orders of magnitude higher cyto- and geno-toxicity than any of the regulated DBPs. Specifically, the USEPA has highlighted several DBPs for possible regulatory action in the near future. Among these DBPs, nitrosamines and chlorate have drawn significant attention within the last decade and are expected to be discussed during the EPA’s six-year review of the Stage 2 DBP Rule in 2016.
While there are multiple ways to control the formation of a specific DBP, it can lead to an unintended increase in the formation of another DBP. For instance, to comply with the Stage 2 DBP Rule, many utilities have been switching to chloramination in order control the formation of halogenated DBPs. Unfortunately, nitrosamines (a group of probable human carcinogen associated with 10-6 lifetime cancer risk at concentrations as low as 0.2 ng/L) are DBPs that have been associated with chloraminated drinking water systems. Among nitrosamines, N-nitrosodimethylamine (NDMA) is the most frequently detected and is likely to receive regulatory attention in the near future. However, removal of NDMA precursors is more challenging than regulated DBP precursors (THMs, HAAs). Control strategies such as oxidation of precursor material or switching disinfection strategies may lead to unintended formation of regulated THMs and HAAs, formation of other unregulated DBPs, and formation or introduction of inorganic DBPs such as bromate, chlorate, chlorite, and perchlorate. Therefore, utilities intent on using oxidation as a control strategy should also consider the impacts on the formation of other regulated (THMs, HAAs) and other DBPs (NDMA, chlorate). This study evaluates the advantages and disadvantages associated with the use oxidants as well as offers a look forward to potential future regulations regarding DBPs. The trade-offs of the various treatment techniques are evaluated and summarized to provide a comprehensive guidance for utilities to prepare and subsequently manage potential Stage 3 DBPs regulations.
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