Highly enhanced degradation of organic pollutants in hematite/sulfite/photo system

Sulfate radical (SO4 center dot-)-based advanced oxidization processes (SR-AOPs) are most commonly explored by activation of peroxydisulfate (PDS), peroxymonosulfate (PMS) or sulfite by various transition-metal ions with or without UV irradiation. Here sulfite activation in the presence of hematite (alpha-Fe2O3) under UV (hematite/sulfite/photo) in the presence of O-2 was successfully developed. The performance of this system towards organic pollutant degradation was evaluated, and the reactive species involved were identified. The results demonstrated that roxarsone (ROX), an aromatic organoarsenic pollutant, could be effectively degraded by this system and the degradation efficiency was greatly affected by initial pH, hematite dosage, and sulfite concentration. Replacement of Na2SO3 with CaSO3 greatly improved the degradation efficiency, and the same amount of sulfite source applied with multiple-dosing mode was more beneficial to pollutant removal than the single-dosing mode. The quenching experiments, electron spin resonance (ESR) spectra, and high-performance liquid chromatography with mass spectrometry (HPLC-MS) analysis of the reaction products showed that SO4 center dot- radicals mainly contributed to the highly efficient ROX degradation. This system also had high degradation efficiencies towards other recalcitrant organic pollutants, such as atrazine, bisphenol A, rhodamine, and methylene blue and could use sunlight instead of artificial UV irradiation. This work provides a practical and cost-effective method for degrading recalcitrant organics in wastewaters, and also exhibits a beneficial treatment strategy to replace Na2SO3 with CaSO3 to enhance the decay of organics, and thus advances the application of this oxidation system.