GAC removal of organic nitrogen and other DBP precursors

Abstract

The increased mutagenicity of disinfection by‐products (DBPs) containing bromide (Br−) and nitrogen requires a renewed evaluation of best available treatment technologies for DBP control. The aim of this article is to document the removal of organic nitrogen during granular activated carbon (GAC) treatment and to illustrate how GAC treatment alters DBP speciation. Rapid small‐scale column tests (RSSCTs) with GAC were conducted on pretreated surface water sources to evaluate the simultaneous removal of carbonaceous and nitrogenous DBP precursors: dissolved organic nitrogen (DON), dissolved organic carbon (DOC), organics absorbed by ultraviolet light at 254 nm (UV254), and Br−. Simulated distribution system tests were conducted with RSSCT effluent samples throughout natural organic matter breakthrough, and free chlorine was used to evaluate the formation of halogenated carbonaceous and nitrogenous DBPs. GAC preferentially removed UV254‐absorbing material over DOC, which was removed more effectively than DON. Br− was not removed. Consequently, effluent ratios of Br− to DOC and Br− to DON changed during GAC treatment, and the ratio of brominated DBPs to chlorinated DBPs shifted during the GAC breakthrough cycle; brominated DBPs dominated earlier in the breakthrough of DOC. Neither DON nor nitrogenous DBP precursors were removed efficiently during GAC treatment.

Re‐assessing effects of bromide and granular activated carbon on disinfection byproduct formation

“…At a low TOC concentration and a high Br/TOC ratio, formation of brominated THMs may dictate the speciation due to fast reaction kinetics (Summers et al, 1993). As shown in Figure 3, BIF values consistently increased after GAC, as reported in previous studies (e.g., Chiu et al, 2012;Krasner et al, 2016). These researchers have postulated that GAC adsorption preferentially removes the hydrophobic fraction of organic matter, leaving hydrophilic fraction and bromide in treated water.…”

“…It is well established that GAC adsorption can lead to a higher BIF in treated water (Amy et al, 1991;Chiu et al, 2012;Stanford, 2017;Summers et al, 1993;Symons et al, 1993). However, this analysis shows that the TOC removal by GAC may offset the increase in BIF, especially before 50% of bed exhaustion is reached when considering Br-THM3 as a surrogate metric.…”

“…Because it often exists in a much higher concentration (in mg/L) than trace organics (in μg/L or ng/L) in water, NOM can interfere with the adsorption of trace organics and be removed by GAC simultaneously. Removal of NOM reduces the formation of most disinfection byproducts (DBPs) in treated water following postchlorination (Chiu, Westerhoff, & Ghosh, 2012;Singer, 1994). Lower organic matter in water also reduces disinfectant dosage and helps maintain disinfectant residuals in distribution systems (Roth & Cornwell, 2018).…”

“…Extensive research has been conducted on the effect of GAC on DBP formation in the presence of bromide in water (Amy, Tan, & Davis, 1991;Chiu et al, 2012;Jiang, Li, Zhang, Liu, & Zhu, 2018;Krasner et al, 2016;Stanford, 2017;Summers, Benz, Shukairy, & Cummings, 1993;Symons, Krasner, Simms, & Sclimenti, 1993). GAC removes dissolved organic matter (often measured as total organic carbon, TOC) but has little effect on bromide.…”

Formation and removal of disinfection by-products in a full scale drinking water treatment plant

“…Coagulation can effectively remove the humic substances with a high hydrophobic character but will be much less effective for the hydrophilic fractions; then activated carbon could be useful for the removal of these remaining fractions (Bond et al 2011). Activated carbon (GAC) is considered as an advanced treatment for NOM removal through adsorption and/or biodegradation (Yang et al 2010;Chili et al 2012;Fu et al 2017) for the control of DBP formation. However, only few studies deal with the interest of GAC for the removal of DBPs preformed from pre-chlorination or intermediate chlorination (Tung et al 2006;Kim and Kang 2008;Cuthbertson et al 2019).…”