Chlorine Reuse in UV/Electrochemical Oxidation to Advance Sewage Cotreatment of Landfill Leachate

Landfill leachate cotreatment with municipal sewage remains a widespread practice in waste management. However, the quality of the resulting effluent is often compromised by dissolved organic matter (DOM) from leachate, especially when it exhibits high ultraviolet absorbance at 254 nm (UV). While degrading the DOM through oxidation is a promising approach, substantial chemical dosing is required for landfill leachate. An emerging alternative is electrochemical oxidation with ultraviolet radiation (UV/EO), which generates chlorine and its derived radicals in situ. Yet, prolonged UV/EO introduces concerns of residual chlorine accumulation and consequent toxicity. In response, we adapted UV/EO to reuse the residual chlorine, wherein partially replacing the treated leachate with untreated volumes reduced the UV of the subsequent batch. The energy efficiency of the chlorine-reuse process was optimized by using the response surface methodology, adjusting the applied current density and Reynolds number. We incorporated a UV dechlorination unit in sequence, eliminating formulas recalcitrant to UV/EO and resulting in an overall 81% reduction in UV. Particularly in areas with established cotreatment infrastructures, this approach advances landfill leachate management, having demonstrated minimal risks of acute toxicity and genotoxicity upon discharge with municipal sewage at 3% v/v.