Electrochemical Dechlorination of Municipal Wastewater Effluent

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.