Electrochemical advanced oxidation for treating ultrafiltration effluent of a landfill leachate system: Impacts of organics and inorganics and economic evaluation

Abstract

We treated landfill leachate using electrochemical advanced oxidation processes (EAOPs) with a boron-doped diamond (BDD) anode. Before EAOPs, the leachate was first treated using biological treatment (anoxic–aerobic) and then ultrafiltration (hereafter referred as biopretreated UF landfill leachate). We explored impacts of organics and inorganics (nitrogen – and chloride – species) for various current densities (1–80 mA/cm2). We found that EAOPs enhanced biodegradability (BOD/COD ratio) significantly from < 0.03 to up to 0.78. COD destruction followed a pseudo-first order model, with the rate constant and electric energy per order ranging from 0.91 to 28.29 h−1 and 17.1 to 127.5 kWh m−3, respectively. The current efficiency (CE) was 100% for current density 1 mA/cm2 and CE decreased to 57.8% as the current density increased to 30 mA/cm2. The oxidation priority was in this order: COD > nitrogen – species > chloride – species. The evolution of nitrogen – and chloride – species and their oxidation mechanisms were also investigated. The impact of Fickian diffusion and electrical field driven charged ion transport (EFDCIT) on the total mass transport was examined using the Nernst-Planck equation. We found that the contribution of EFDCIT was similar to diffusion for current densities higher than 64 mA/cm2. Finally, we compared the costs for standalone EAOPs and EAOPs integrated with subsequent biological treatment for biopretreated UF landfill leachate and found that the lowest cost for the latter one that meets the effluent discharge criteria was only 0.76 USD/m3. Our study proved that EAOPs are technically and economically promising technology for leachate treatment.