Removal and transformation characterization of refractory components from biologically treated landfill leachate by Fe2+/NaClO and Fenton oxidation

Treatment of effluent from biological unit for landfill leachate by NaClO enhanced Fe2+ coagulation (Fe2+/NaClO) followed by Fenton oxidation was studied. Firstly, removal of COD, NH4+, and color degree by individual coagulation, NaClO oxidation and Fe2+/NaClO process was compared under the condition of 10 mmol L−1 FeSO4 and 12.5 mmol L−1 NaClO. COD removal in the Fe2+/NaClO process was 53.5%, which was higher than 23.5% and 12.5% in the individual Fe2+ coagulation or NaClO oxidation, respectively. And, NH4+ removal was nearly same in the Fe2+/NaClO and individual NaClO oxidation process. Furthermore, the removal efficiency of COD was increased to be 86.0% via Fenton oxidation with a 40 mmol L−1 Fe2+. Based on the fraction results via ultrafiltration membranes, it was observed that the fractions with molecular weight ranging from 100 to 30 kDa were efficiently removed via the coagulation process. The fractions with molecular weight less than 10 kDa were mainly removed via the Fenton oxidation. Based on the resin fractionation results, the fractions of the hydrophilic matter and hydrophobic acids dominated in the effluents from biological unit. The fractions of hydrophobic neutrals and hydrophobic bases were largely removed via the Fenton oxidation process.