Advanced treatment of landfill leachate reverse osmosis concentrate via an integrated coagulation–sedimentation–electrochemical oxidation–biological aerated filter process

Abstract

Reverse osmosis membrane filtration concentrate is a type of organic wastewater from landfill leachate treatment that has a high concentration of organic matter, refractory macromolecules, and low biodegradability. The reverse osmosis concentrate was treated in this study using a combination of physicochemical and biological processes. Single-factor test analysis for coagulation and sedimentation indicated that 2000 mg L⁻¹ of polymeric ferric sulphate (PFS), a pH of 7, and a precipitation time of 40 min yielded the best removal effect. The COD, NH₃–N, and UV₂₅₄ removal efficiencies were 74%, 34%, and 64%, respectively. The influent of the electrochemical oxidation is the effluent pretreated by coagulation and precipitation. The anode material was a ruthenium–iridium–titanium plate electrode, and the cathode material was a stainless-steel plate electrode. The removal efficiencies of COD, NH₃–N, and UV₂₅₄ in the electrochemical oxidation process were 67%, 83%, and 80%, respectively. The BOD₅/COD ratio increased to 0.5, and the unit energy consumption of COD was 39.4038 kW h kg⁻¹. The electrochemical oxidation effluent was then subjected to advanced treatment in an aerated biological filter. The influent flow rate was 0.3 L h⁻¹, the air-to-water ratio was 4 : 1, and the temperature was 20 °C–30 °C. No glucose was added to the subsequent influent. The COD, NH₃–N, and UV₂₅₄ removal efficiencies were 71%, 73%, and 69%, respectively. Following biological treatment in the aerated biological filter, the B/C ratio of the reverse osmosis membrane concentrate improved. The operational results of the combined processes indicated removal efficiencies of 97%, 98%, and 97% for COD, UV₂₅₄, and NH₃–N, respectively. The effluent quality attained the Class A standard of the Pollutant Discharge Standard for Urban Sewage Treatment Plants (GB18918-2002).