Sequential coagulation and Fe0-O3/H2O2 process for removing recalcitrant organics from semi-aerobic aged refuse biofilter leachate: Treatment efficiency and degradation mechanism

Abstract

Landfill leachate effluent obtained after semi-aerobic aged refuse biofilter (SAARB) treatment still contains various recalcitrant organics. In this study, a sequential coagulation and Fe0-O3/H2O2 process was developed for treating SAARB leachate. The effects in terms of degradation of recalcitrant organics and the related mechanisms due to the coagulation and Fe0-O3/H2O2 processes were systematically explored and discussed. The results indicated that polymerized ferric sulfate was the most efficient coagulant for treating SAARB leachate where the chemical oxygen demand (COD), UV254, and CN removal efficiencies were 59.60%, 63.22%, and 70.32%, respectively. In the Fe0-O3/H2O2 process under the optimized conditions comprising Fe0 dose = 0.6 g/L, O3 dose = 26.80 mg/min, H2O2 dose = 1.0 mL/L, and reaction time = 20 min, the COD, UV254, and CN removal efficiencies with the coagulated supernatant were 43.39%, 59.47%, and 93.20%, respectively, and the biodegradability (biochemical oxygen demand/COD) improved greatly from 0.06 to 0.34. Analysis of UV–Vis and 3D-EEM spectra indicated that coagulation-resistant substances in the SAARB leachate could be effectively degraded and destroyed by the Fe0-O3/H2O2 process. In the O3/H2O2 environment, Fe0 generated Fe2+ and iron oxides (Fe2O3, Fe3O4, and FeOOH) with homogeneous and heterogeneous catalytic roles against O3/H2O2 to produce reactive oxygen species. Furthermore, Fe(OH)2 and Fe(OH)3 colloids contributed to the removal of organics to some extent via adsorption and precipitation effects. In conclusion, the proposed sequential coagulation and Fe0-O3/H2O2 process is an efficient method for treating recalcitrant organics in SAARB leachates.