Advanced Treatment of Landfill Leachate Reverse Osmosis Concentrate via 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 the coagulation and sedimentation indicated that 2000 mg/L of polymeric ferric sulphate (PFS), pH7, precipitation time 40 min yielded the best removal effect. COD, NH3-N, and UV254 removal efficiency are 73.865%, 33.927%, and 64%. The influent of 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 67.29%, 82.70%, and 80.29%, respectively. BOD5/COD ratio increased to 0.5, and unit energy consumption of COD was 39.4038 kWh/kg. Electrochemical oxidation effluent was then subjected to advanced treatment in an aerated biological filter. The influent flow rate 0.3 L/h, the air-to-water ratio was 4:1, and temperature 20~30 °C. No glucose was added to the subsequent influent. COD, NH3-N, and UV254 removal efficiencies were 71.29%, 73.21%, and 69.39%. Following biological treatment in the aerated biological filter, the B/C ratio of the reverse osmosis membrane concentrate improved. Combined process's operational results indicate that the removal efficiencies of COD, UV254, and NH3-N are 97.46%, 98%, and 96.8%. The effluent quality attained the Class A standard of the Pollutant Discharge Standard for Urban Sewage Treatment Plants (GB18918-2002).