The use of sodium bisulfite as an electron donor to quench chloramine disinfectant residuals in municipal wastewater effluents prior to discharge incurs the cost of purchasing and transporting bisulfite to the utility and increases the loading of salts to the receiving water. In this study, degradation of chloramine residuals within authentic municipal wastewater effluents was achieved within a 30 min timescale using a reductive electrochemical reactor, which supplied electrons via a stainless-steel cathode under galvanostatic conditions without an ion exchange membrane separating the cathode and anode. Application of a 0.26 mA/cm2 cathodic current density reduced chloramines to ammonia and avoided oxidation at the IrO2-coated titanium anode of chloride to chlorine or chlorate and of ammonia to nitrite or nitrate. Net chloramine production was observed at a higher current density (2 mA/cm2). Chloramine degradation rates and Coulombic efficiencies were highest and electrical energy per order (E EO) values were lowest for the 304-grade stainless-steel cathode, which contains the highest nickel content, and for a stainless-steel cathode with a high surface area. Differences in ionic strength and pH were less important. For chloraminated municipal wastewater samples, the highest Coulombic efficiency was 4.1% and the lowest E EO value was 0.08 kWh/m3. An initial comparison indicated that the electricity cost associated with this E EO value would be comparable to the cost of sodium bisulfite for areas with low electricity costs.
Recent research indicates that the poorly characterized high-molecular weight disinfection byproduct (DBP) fraction (more than two carbons) contributes more to cytotoxicity than the one- to two-carbon DBPs of current interest. Peptides and lipids contribute to DBP precursors in water supplies. Although partially degraded, a portion of their monomers retain their structures. Using tyrosine and oleic acid as exemplars, this study illustrates the targeted analysis of their chlorinated byproducts as an approach to characterizing high-molecular weight DBPs. After biopolymers had been digested to liberate monomers, oleic acid was detected in four of six secondary effluents from potable reuse facilities at concentrations of up to 91 nM (47 μg/L), while its chlorohydrins were detected in two effluents at concentrations of up to 1.3 nM (0.43 μg/L). Tyrosine was detected in all six effluent samples at concentrations of up to 42 nM (7.6 μg/L). 3-Chlorotyrosine was detected in four samples at concentrations of up to 3.3 nM (0.71 μg/L), and 3,5-dichlorotyrosine was detected in three samples at concentrations of up to 2.1 nM (0.53 μg/L). These DBPs were detected in conventional drinking waters, but at lower frequencies and concentrations. When detected, the contribution of chlorohydrins to cytotoxicity was comparable to some, but not all, of the one- to two-carbon DBP classes.
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