Effective removal of refractory organic contaminants from reverse osmosis concentrated leachate using PFS-nZVI/PMS/O process.

Reverse osmosis concentrated leachate (ROCL) from landfill leachate treatment contains high amounts of refractory organics. In this study, a combination of polymerized ferric sulfate (PFS) and nanoscale zero-valent iron/peroxymonosulfate/ozone (nZVI/PMS/O) approach was adopted to remove refractory pollutants in ROCL. The effects of coagulant species, dosage and initial pH on the pre-treatment of organics from ROCL during coagulation process were investigated. Moreover, the influences of experimental factors, including initial pH, ozone doses, PMS, and nZVI on the removal of refractory organics in ROCL from coagulation effluent were systematically studied. The characteristics of organics were determined by using microscopic, spectroscopic and electron paramagnetic resonance (EPR) analyses. The batch experimental results indicated that the refractory organic contaminants in ROCL were effectively removed through PFS-nZVI/PMS/O treatment. The maximum removal efficiencies of COD and TOC were 89.1% and 83.2% under the optimum conditions: PFS of 8 g/L, ozone dose of 100 mg/min, PMS dose of 1.5 mM and nZVI dose of 10 mM, and at these conditions, the biodegradability index (BOD/COD) was enhanced from 0.02 to 0.32. The excitation-emission matrix fluorescence spectroscopy (EEM) analysis indicated that humic-like and fulvic-like substances in ROCL were effectively removed. According to EPR analysis, hydroxyl and sulfate radicals were the dominant reactive species for the degradation of organics in nZVI/PMS/O system. Overall, the environmental and economic analysis suggested that the PFS-nZVI/PMS/O system was a cost-effective method for cleaning refractory organics from ROCL.