Enhanced degradation of refractory organics in concentrated landfill leachate by Fe-0/H2O2 coupled with microwave irradiation

To study the treatment effect and mechanism of a combined microwave (MW)-Fe-0/H2O2 Fenton-like process on concentrated landfill leachate, the effects of initial pH, Fe-0 dosage, H2O2 dosage, MW power and reaction time on the removal of organic substances were investigated. The phase change of Fe-0 before and after reaction and its catalytic mechanism were investigated using multiple analytical techniques. Results showed that the removal efficiencies of chemical oxygen demand, UV254 and color number were 58.70%, 85.69% and 88.30%, respectively, at initial pH of 2.0, Fe-0 dosage of 0.5 g/L, H2O2 dosage of 20 mL/L, MW power of 400 W and reaction time of 14 min. Comparison of different Fenton-like processes indicated that the MW-Fe-0/H2O2 Fenton-like process was the most efficient and significantly decreased the aromaticity degree, molecular weight and condensation degree of organic substances in the leachate. The fluorescence peak of concentrated leachate exhibited a blue-shift in the MW-Fe-0/H2O2 process, further indicating that the condensation degree of humic substances declined and molecular weight remarkably decreased. The mechanism exhibited an advanced oxidation effect of a heterogeneous Fenton reaction between iron oxide and H2O2, as well as of adsorption and precipitation effects of iron-based colloids, on organic substances. Moreover, thermal and non-thermal effects of MW accelerated these reactions, achieving fast removal of organic pollutants in the concentrated landfill leachate. Overall, the results of this study showe that the MW-Fe-0/H2O2 process is an effective and promising method to handle concentrated landfill leachate.