Improved oxidation of refractory organics in concentrated leachate by a Fe2+-enhanced O3/H2O2 process

Concentrated leachate from membrane processes, which contains a mass of refractory organics and salt, has become a new problem for wastewater engineers. In this study, removal of organic contaminants in concentrated landfill leachate was investigated by applying the ferrous ion (Fe2+) catalyzed O-3/H2O2 process. The maximum chemical oxygen demand (COD) and absorbance at 254 nm (UV254) removal efficiencies under the optimal conditions (initial pH = 3.0, Fe2+ dosage = 6.500 mM, H2O2 dosage = 18.8 mM and O-3 dosage = 52.65 mg min(-1)) were 48.82% and 63.59%, respectively. These were higher than those achieved using the Fe2+/O-3, O-3/H2O2, and O-3 processes, and biodegradability of the leachate was improved significantly. Moreover, compared with other processes, the Fe2+ had a stronger catalytic effect. Molecular distribution analysis and three-dimensional excitation and emission matrix analysis both indicated that the fulvic acid and humic acid in the concentrated leachate were greatly degraded. Ultraviolet-visible spectra showed that the Fe2+/O-3/H2O2 process mainly destroyed unsaturated bonds and decreased the aromatic degree of the leachate. The reaction mechanism of the Fe2+/O-3/H2O2 process mainly was attributed to three factors: (1) O-3 and H2O2 reacting to produce (OH)-O-center dot; (2) H2O2 and O-3 decomposing into (OH)-O-center dot through the oxidation of Fe2+ to Fe3+; and (3) coagulation by Fe (OH)(3). The (OH)-O-center dot can rapidly degrade recalcitrant organics, and coagulation also increases the removal of organic matter. Therefore, the Fe2+/O-3/H2O2 process was an effective method for treating concentrated landfill leachate.