Role of inorganic anions on the performance of landfill leachate treatment by electrochemical oxidation using graphite/PbO2 electrode

Abstract

The influences of sulfate, chloride, nitrate, and bicarbonate ions on the electrochemical treatment performances of landfill leachate have been investigated. The concentrations of SO42−, Cl−, NO3− ions, and bicarbonate alkalinity of landfill leachate were 252 mg L-1, 1244 ± 22.3 mg L-1, 12 mg L-1, and 1750 ± 40.8 mg L-1 as CaCO3 without any external salt addition. The concentrations of anions were analyzed after 2 h of electrochemical oxidation to understand any conversion of externally added anions. Chemical oxygen demand (COD), dissolved organic carbon (DOC), and ammonia-nitrogen removal efficiencies after 2 h of electrolysis were 35.1 ± 2.3 %, 25.6 ± 2.9 %, and 97.6 ± 0.7 % respectively. Although no effect was observed for COD and DOC removal, increasing sulfate ion adversely affected NH3-N removal efficiency; the removal percentage decreased to 87.7 ± 0.5 % for 6082 mg L-1 of SO42− containing leachate. Addition of chloride improved the overall system performance. Obtained COD and DOC removal efficiencies were 67.2 ± 1.5 % and 55.8 ± 2.1 % for Cl− concentration of 4361 mg L-1 in leachate. Very low NH3-N removal (60 ± 2.1 %) for 1483 mg L-1 of nitrate containing leachate was obtained in this study due to the regeneration of ammonia by cathodic reduction of nitrate. Nitrate formation was observed as part of reactions for ammonia removal; for instance, the nitrate concentration increased from 12 mg L-1 to 39.3 ± 4 mg L-1 after electrolysis. For the leachate treatment containing 6000 mg L-1 of externally added HCO3−, the COD and DOC removal efficiencies decreased to 19.6 ± 0.6 % and 17.8 ± 1.1 %, but the more adverse effect was observed for NH3-N removal efficiency which was only 7.4 ± 1.8 %.