Submerged arc plasma treatment of landfill leachate with a high proportion of refractory organics: Degradation performance and biodegradability enhancement

Abstract

Efficient treatment of landfill leachate remains a challenge because of the load and highly stable recalcitrant organics. Herein, pre-treatment of real stabilized leachate was realized in a submerged arc plasma (SAP) reactor to which microbubbles with different carrier gases (air, N2, and O2) were introduced to preserve the subsequent biological process. We performed a detailed parametric analysis (applied voltage, electrode material, carrier gas, and initial pH) to determine the optimum operational conditions of organics degradation and leachate biodegradability improvement. Besides, degradation kinetics, reaction mechanism, and electrical energy consumption were studied during the SAP process. Ion exchange resin was initially used to effectively reduce the ionic strength of the bulk solution to allow expanding the plasma discharge area. The biodegradability of leachate was outstandingly enhanced, as reflected by an increase in BOD5/COD ratio from 0.08 to 0.68 in O2 discharge within 120 min. Meanwhile, stainless-steel as a grounded electrode outperformed aluminum, brass, and copper. The SAP also exhibited excellent performance for organics decomposition, which was found to follow second-order and approximately pseudo-second-order kinetics. Meanwhile, the possible mechanism of organics destruction was proposed based on COD measurements and reactive species trapping experiments, demonstrating the prevailing contribution of H2O2 and 1O2, among others. Nonetheless, the SAP process of leachate treatment required relatively high energy consumption (18,400 kWh/m3). The study demonstrated an effective and robust pre-treatment process for the subsequent bioremediation of landfill leachate containing chemically stable and recalcitrant organics not treatable by conventional techniques.