Hydroxyl radical-based and sulfate radical-based photocatalytic advanced oxidation processes for treatment of refractory organic matter in semi-aerobic aged refuse biofilter effluent arising from treating landfill leachate.

In this study, three photolytic advanced oxidation processes (AOPs) were applied to the treatment of refractory organic matter in semi-aerobic aged refuse biofilter (SAARB) effluent, and the treatment efficiencies of the three AOPs were systematically compared. The AOPs combined ultraviolet (UV) radiation with either hydrogen peroxide (UV-H2O2), peroxymonosulfate (UV-PMS) or both oxidants (UV-PMS/H2O2). The effects of key parameters on degradation characteristics of refractory organics, and the contribution of reactive oxygen species were systematically studied. Results indicated that UV radiation can greatly enhance treatment efficiencies of both PMS and H2O2. Furthermore, decreasing n(H2O2)/n(PMS) ratio and decreasing the reaction pH can increase treatment efficiency for refractory organics. Compared on the basis of chemical oxygen demand (COD), treatment efficiency followed the order UV-PMS (COD removal 37.39%) > UV-PMS/H2O2 (30.51%) > UV-H2O2 (28.59%) which is consistent with results from ultraviolet-visible spectra analysis. HO• and SO4•- were both identified in the UV-PMS/H2O2 and UV-PMS processes. In the UV-PMS process, SO4•- was the dominant ROS, which suggested that SO4•--based AOPs are better than HO•-based AOPs for degrading refractory organics contained in SAARB effluent. Parallel factor (PARAFAC) analysis indicated that UV-based AOPs were effective in degrading humic- and fulvic-like substances in the SAARB leachate, and the UV-PMS process achieved a much better degradation efficiency of refractory organics in the leachate than did the UV-PMS/H2O2 and the UV-H2O2 processes. Furthermore, the best treatment efficiency was achieved by the UV-PMS process and this process also consumed the least electrical energy. This study provides a theoretical reference for refractory organics degradation in SAARB effluent by UV-catalyzed AOPs.