Transformation of pollutants in landfill leachate treated by a combined sequence batch reactor, coagulation, Fenton oxidation and biological aerated filter technology

A combination process was developed including sequence batch reactor (SBR), coagulation, Fenton oxidation, and biological aerated filtering (BAF) in series for the purpose of removing pollutants in landfill leachate. The high contents of dissolved organic matters (DOM) of landfill leachate in each treatment process were fractionated into humic acid (HA), fulvic acid (FA), and hydrophilic (HyI) fractions. The composition changes and characteristics of DOM were investigated. Subsequently, seventy organic micropollutants in raw leachate were detected, and twenty-five organic pollutants were completely removed by SBR process. Low organic pollutants and high turbidity removals were achieved by coagulation. Thirty-seven organic micropollutants disappeared completely in Fenton effluent and low molecular weight fractions were removed by BAF preferentially. A total reduction of COD (98.4%), BOD5 (99.1%), NH4-N (99.3%), TP (99.3%), SS (91.8%), turbidity (99.2%) and color (99.6%) achieved in the final BAF effluent indicated the effectiveness of the combined plant. Moreover, metal ions of Cu, Ni, Zn, Mn, Cr, Mg, Pb, Cd, Al, Fe and anions of SO42−, Cl−, NO3−, NO2−, and PO43− in raw leachate and four treated effluents were measured, respectively. The observations indicated that leachate treated by the combined process still contained higher concentration of total heavy metals and inorganic anions than the surrounding water environment, though no violation to effluent standard was found. The possible risk in leachate should not be negligible because landfill leachate was still one of the major sources of heavy metals and inorganic pollutants discharged to the surrounding environment.

Research highlights▶ The fates of various pollutants in a combined landfill leachate treatment were investigated. ▶ The level of organic pollutants in combined effluent met standard for wastewater discharge. ▶ The concentration of total heavy metals should not be negligible in combined treatment effluent.