Development of an advanced electrooxidation reactor with gas recycling for efficient treatment of pretreated landfill leachate nanofiltration concentrates

In this study, we present the development of an advanced electrooxidation (EO) reactor with integrated gas recycling for efficient treatment of pretreated landfill leachate nanofiltration (NF) concentrates. Gases generated during the EO process, such as Cl₂, ClO₂, O₂, and H₂, were recirculated into the reactor to enhance indirect oxidation and improve pollutant removal. The effects of anode material (BDD, DSA, and hybrid), current density, and initial pH were investigated. Under optimal conditions (m_coagulant = 800 mg Al³⁺/L, anode = BDD, j = 33.3 mA/cm², and pH = 5.1), removal efficiencies reached 77.8 % for COD, 70.6 % for TOC, 95.5 % for TKN, and 94.0 % for NH₃-N. The advanced EO reactor demonstrates a 12.5 % decrease in specific energy consumption, while achieving superior removal efficiencies of approximately 5–6 % for COD and TOC, and 2.5–3.5 % for TKN and NH₃-N, compared to a conventional batch reactor under the same conditions. The BDD anodes performed better in organic removal, while DSA anodes were more effective for NH₃-N oxidation. Hybrid anode combinations provided balanced results with no observed synergy or antagonism. We also evaluated energy consumption, active chlorine production, nitrate accumulation, and AOx formation. Gas recirculation reduced harmful emissions and enhanced reactor performance by increasing the residence time of oxidizing species. This reactor design provides a sustainable and energy-efficient solution for treating biologically resistant NF concentrates from landfill leachate. The results demonstrate the potential of integrating gas management into EO systems to improve treatment efficiency and reduce environmental impact, making it a viable option for advanced wastewater treatment applications.