Electrochemical oxidation of pretreated landfill leachate nanofiltration concentrate in terms of pollutants removal and formation of by-products

This study compares the efficiencies of active (Ti/TiO₂–RuO₂–IrO₂ (TIR)) and inactive (Ni/Boron Doped Diamond (BDD)) anodes in terms of pollutant treatment and by-product formation in pretreated (chemical coagulation) landfill leachate nanofiltration membrane concentrate (PLNC). PLNC has high chemical oxygen demand (COD:4900 mg/L), total organic carbon (TOC: 1874 mg/L), total Kjeldahl nitrogen (TKN: 520 mg/L), ammonium nitrogen (NH₃–N: 21.35 mg/L), chloride (5700 mg/L) and sulfate (9000 mg/L – due to coagulant type). The parameters of COD, TOC, NH₃–N, TKN, free and combined chlorine species, halogenated organic compounds (HOCs), adsorbable organic halogens (AOX), and nitrate at different current density (J: 111–555 A/m²) and initial pH (pH_i:3.5–7) were compared for both anodes. The removal efficiencies at the optimum conditions (pH_i 5.5, 333 A/m² and 8 h) were obtained as 86.4% COD, 77.4% TOC, 93.4% TKN, 94.4% NH₃–N with BDD and 34.3% COD, 27.3% TOC, 93.7% TKN, 97.4% NH₃–N with TIR. According to gas chromatography-mass spectrometry (GC-MS) results obtained under optimum conditions, haloalkane/alkene, halonitroalkane, halonitrile, haloketone, haloalcohols, haloacids, haloaldehydes, haloamines/amides on both electrodes were detected as species of HOCs. In addition, the highest nitrate concentration was observed at the TIR anode, while the highest AOX concentration was observed at the BDD anode.