Ordering Information:
ORDER NUMBER:  91206
DATE AVAILABLE: Spring 2008

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PRINCIPAL INVESTIGATORS:
Stuart W. Krasner, Paul Westerhoff, Baiyang Chen, Gary Amy, Seong-Nam Nam, Zaid K. Chowdhury, Shahnawaz Sinha, and Bruce E. Rittmann

OBJECTIVES:
The objectives of this project were to (1) determine the formation, occurrence, and control of disinfection by-products (DBPs) and DBP precursors in wastewater and their impact on downstream drinking water sources; (2) evaluate the fate and transport of wastewater-derived DBPs and precursors in receiving waters, as well as their removal through different drinking water unit processes; and (3) evaluate treatment strategies at wastewater and drinking water treatment plants to reduce DBPs that best balance societal benefits.

BACKGROUND:
In addition to water recycling and reclamation programs, indirect potable reuse of wastewater has occurred as upstream wastewater treatment plants discharge water into rivers or lakes that serve as downstream drinking water supplies. Wastewater treatment plants are sources of DBPs, if chlorine disinfection is practiced, and DBP precursors. Many different biological, physical, and chemical unit processes are employed by wastewater treatment plants, which can produce a wide range of treated water qualities.

HIGHLIGHTS:
Nitrification impacted the quality of wastewater effluent organic matter (EfOM) in terms of wastewater parameters, natural organic matter (NOM) character, and DBP-related parameters. The addition of chlorine to poorly nitrified EfOM often formed chloramines, relatively low levels of halogenated DBPs, and often significant amounts of N-nitrosodimethylamine (NDMA). The reactivity of EfOM to form many halogenated DBPs was typically less than that of NOM. However, EfOM was richer in nitrogenous DBP precursors (e.g., NDMA). Wastewater-derived DBPs and DBP precursors can be removed to varying degrees along the length of a river by photolysis (NDMA), volatilization (chloroform), and biodegradation (DBP precursors).

APPROACH:
The researchers (1) conducted a full-scale survey of wastewater and drinking water plants, as well as effluent-impacted rivers, lakes, and groundwaters; (2) compiled a database of first-principle fate-and-transport parameters for DBPs; (3) performed DBP and DBP precursor fate-and-transport bench-scale experiments; (4) evaluated the treatability of EfOM with drinking water treatment processes.; (5) used simple and advanced NOM characterization techniques; (6) measured regulated and emerging DBPs, as well as conducted formation potential tests; and (7) analyzed for a pharmaceutical (primidone) that is a conservative tracer of wastewater influences in drinking water supplies.

RESULTS/FINDINGS:
THM precursors in wastewater were most likely associated with humic substances (e.g., from residual drinking water NOM). The amount of THM precursors present was roughly the same for the different biological wastewater treatment processes, whereas soil aquifer treatment and reverse osmosis removed THM precursors. Treated wastewater was a source of DON that could be a source of precursors for HANs and NDMA. Wastewater treatment plants that achieved some nitrification tended to reduce the level of HANs and/or NDMA precursors. In receiving waters, volatilization was the dominant loss mechanism for chloroform and biodegradation was the major loss mechanism for dichloroacetic acid. Several mechanisms can contribute to the loss of dichloroacetonitrile. Photolysis was the dominant loss mechanism for NDMA in a fast, shallow river, but was a minor loss mechanism in a slow, deep river. Many DBP precursors in EfOM can decrease in concentration along the length of the river due to biodegradation. In addition to treatment upgrades at drinking water or wastewater plants, there may be other alternatives (e.g., soil aquifer treatment, riverbank filtration) for reducing the effect of EfOM on drinking water supplies.

IMPACT:
This study developed information on the simultaneous control of wastewater parameters (e.g., ammonia, biochemical oxygen demand), NOM (e.g., DON), and DBPs (e.g., THMs, HANs, nitrosamines, and their precursors). This information can be used in different watersheds to assess how best to invest public money to upgrade wastewater and drinking water treatment plants in order to maximize societal benefits while minimizing the health risks posed by wastewater-derived DBPs. This project also determined the fate and transport of wastewater-derived DBPs and their precursors in receiving waters. This information can be used to develop engineering solutions to minimize wastewater impact on drinking water supplies.

RESEARCH PARTNER:
U.S. Environmental Protection Agency

PARTICIPANTS:
Twenty-three wastewater plants and 9 drinking water treatment plants in the United States participated in this project. In addition, several agencies in the South Platte River watershed participated in this study.