Treatment of membrane concentrated leachate by two-stage electrochemical process enhanced by ultraviolet radiation: Performance and mechanism.

• The optimal conditions of UV-TSE process for treatment of coagulated RO membrane concentrated leachate were determined. • ＞86% of TOC, ＞95% NH 3 -N and ＞99% Chloride were removed by optimal UV-TSE process. • UV-TSE process has the outstanding performance for pollutants removal, especially refractory organics. Membrane systems are widely used for advanced leachate treatments in municipal waste incineration (MSWI) plants, resulting in the production of membrane concentrated leachate containing a high content of pollutants, especially refractory organics and salts. In this study, a two-stage electrochemical (TSE) process enhanced by ultraviolet (UV) radiation was applied to treat coagulated reverse osmosis concentrated leachate. Application of UV radiation throughout the TSE process produced remarkable results for pollutant removal because UV radiation promoted production of free radicals with strong oxidizing ability, which could function with active chlorine to oxidize pollutants, especially refractory organics. After the optimal UV-TSE (i.e., TSE process enhanced by UV radiation) treatment, the chemical oxygen demand, total organic carbon, light-absorbing substances (at 254 nm), ammonia nitrogen, and total nitrogen removal efficiencies were all more than 86%, and that of color, turbidity and chloride were more than 96%, which had better performance than TSE process. Following UV-TSE process, an obvious blue shift was observed in the UV–Vis spectra, with significant decrease in the absorbances in the UV region. The reduction in the intensity of peaks 1 and 2 in 3D fluorescence spectra was 87.37% and 88.90%, respectively. Flow field-flow fractionation analysis showed that the molecular weights of colored dissolved organic matter (DOM), humic-like DOM, and protein-like DOM deeply decreased. The UV-TSE treatment decomposed macromolecular organics into lower molecular organics more effectively and thoroughly, resulting in higher VOCs content in the treated sample, when compared with TSE-treated samples. These findings can shed light on the performance and organics removal mechanism of UV-TSE process, and provide a theoretical basis for the electrochemical treatment of membrane concentrated leachate from MSWI plants. [ABSTRACT FROM AUTHOR]