Removal of Selected C- and N-DBP Precursors in Biologically Active Filters

Oxidants used during drinking water treatment can react with organic matter and bromide/iodide to form disinfection by-products (DBPs) (Knappe 2014, Gan et al. 2013a, Plewa et al. 2004). DBPs in drinking water are a concern to public health because of their various potential health effects (Plewa et al. 2008). The US Environmental Protection Agency (USEPA) has regulated the carbonaceous DBPs (C-DBPs) including total trihalomethanes (THMs) and five haloacetic acids (HAAs) at 80 and 60 μg/L, respectively, in drinking water (USEPA 2006). To meet the stringent Stage 2 Disinfectants and Disinfection Byproducts Rule (D/DBPR), some water utilities in the United States have been switching from chlorine to alternative disinfectants to lower the concentrations of regulated C-DBPs. Although alternative disinfectants such as chlor amine and ozone reduce the formation of regulated C-DBPs, formation of some nitrogenous DBPs (N-DBPs) such as nitrosamines and halonitromethanes (HNMs) have been reported at higher levels than found with disinfection using chlorine (Selbes et al. 2016, Gan et al. 2013a). Furthermore, research has shown that unregulated N-DBPs (e.g., HNMs) exhibit orders of magnitude higher cytotoxicity and genotoxicity than any of the regulated C-DBPs (Plewa et al. 2008, 2004). The USEPA has highlighted nitrosamines for possible regulatory action in the near future (Roberson 2011), as they are a classified as probable human carcinogens and associated with 10–6 lifetime cancer risk at concentrations as low as 0.2 ng/L (USEPA 1993). There are two common approaches to reduce DBP formation, including removing the DBP precursors (e.g., natural organic matter [NOM]) by using treatment technologies like enhanced coagulation, magnetic ion exchange (MIEX1), or granular activated carbon (GAC) before oxidant addition, and switching to alternative disinfectants (e.g., ozone, chloramine, chlorine dioxide). Combined ozone/biofilter treatment leverages both approaches to remove DBP formation potential. The application of ozone is expected to breakdown NOM into smaller, more bioassimilable organic carbon compounds, which can then be degraded across a biofilter, thereby decreasing DBP formation potential (FP) and increasing the biostability of the water before distribution (Brown & Lauderdale 2006). Biologically active filters (biofilters) have been shown to biodegrade a range of organics (both hydrophilic and hydrophobic), including amines, aliphatic aldehydes, phenols, pharmaceuticals, pesticides, algae metabolites, algal toxins, and taste and odor substances (McKie et al. 2015, Snyder et al. 2007, Brown 2006, Brown & Lauderdale Peer Reviewed