N-Nitrosodimethylamine (NDMA) has been considered a carcinogen for some time (Magee et al., 1976), and EPA has calculated the one in one million cancer risk from drinking water to occur at approximately 0.7 ng/L. Along with other members of the nitrosamine family, NDMA received attention in the 1970s in connection with processed foods and beverages, but it was not found in drinking water or domestic wastewater until the turn of the century when analytical methods improved to the point where NDMA could be identified at submicrogram-per-liter levels (Taguchi et al., 1994). Subsequently, NDMA was found in groundwater downgradient of rocket engine testing facilities, in water leaving ion exchange facilities, and in wells influenced by reuse projects (Najm and Trussell, 2001). Recently, as part of EPA’s unregulated contaminant monitoring rule (UCMR2), NDMA was detected in 25 percent of the drinking water distribution systems sampled, at levels between 2 and 600 ng/L. For the most part, these drinking water systems reported that their source water was influenced by wastewater and used chloramines for disinfection (Blute et al., 2010).
NDMA often appears both in raw and treated wastewaters in the United States and Europe (Mitch et al., 2005, Krauss et al., 2009). A 2005 survey of 10 wastewater plants found NDMA in the influent up to 140 ng/L; two plants were 20 ng/L or below, but most were between 20 and 70 ng/L. Effluent samples, however, ranged as high as 960 ng/L (Valentine et al., 2005). Others have reported levels as high as 1,820 ng/L (Gan et al., 2006).
Control of NDMA in treated reclaimed water involves three components: (1) control of the sources of NDMA and its precursors in treatment plant influents, (2) management of the conventional wastewater treatment process, and (3) application of advanced treatment to remove what remains. Both Orange County and Los Angeles have had some success in identifying sources of NDMA and its precursors and have improved the quality of the influent (Valentine et al., 2005). However, it is unclear how much of the NDMA may be the result of domestic sources (e.g., pharmaceuticals, personal care products) that are more difficult to control (Sedlak et al., 2005; Krauss et al., 2009; Shen and Andrews, 2011). Wastewater disinfection practice, particularly chloramination (Pehlivanogllu-Mantas et al., 2006) appears to be an important target. Research by wastewater authorities has demonstrated several factors important to NDMA formation during wastewater chlorination and a number of strategies that may be employed to reduce it (Neisess et al., 2003; Huitric et al., 2005, 2007; Tang et al., 2006; Farée et al., 2011). Although these strategies show promise, NDMA remains an issue in wastewaters disinfected with chloramines, where levels above 100 ng/L are common (Najm and Trussell, 2001; Valentine et al., 2005; Huitric et al., 2007). As a result, facilities designed to produce reclaimed water for direct injection into groundwater include treatment processes designed to remove it (e.g., UV-AOP).
The very nature of wastewater suggests that nearly any substance used or excreted by humans has the potential to be present at some concentration in the treated product. Modern analytical technology allows detection of chemical and biological contaminants at levels that may be far below human and environmental health relevance. Therefore, if wastewater becomes part of a reuse scheme (including de facto reuse), the impacts of wastewater constituents on intended applications should be considered in the design of the treatment systems. Some constituents, such as salinity, sodium, and boron, have the potential to affect agricultural and landscape irrigation practices if they are present at concentrations or ratios that exceed specific thresholds. Some constituents, such as microbial pathogens and trace organic chemicals, have the potential to affect human health, depending on their concentration and the routes and duration of exposure (see Chapter 6). Additionally, not only are the constituents themselves important to consider but also the substances into which they may transformed during treatment. Pathogenic microorganisms are a particular focus of water reuse treatment processes because of their acute human health effects, and viruses necessitate special attention based on their low infectious dose, small size, and resistance to disinfection. Chapter 4 discusses the treatment processes often used to attenuate concentrations of chemical and biological contaminants of suspected health risk to humans.