Enhanced degradation of polychlorinated biphenyls with simultaneous usage of reductive and oxidative agents over UV/sulfite/TiO2 process as a new approach of advanced oxidation/reduction processes

Abstract

This study relies on the UV irradiation of sulfite and TiO2, i.e. UV/sulfite/TiO2 (UST), as a novel method of Advanced Oxidation/Reduction Processes (AORPs) to generate both oxidative and reductive agents, simultaneously for degradation and mineralization of polychlorinated biphenyls (PCBs).The degradation performances of PCBs by UV alone, UV/sulfite (US) and UV/ TiO2 (UT) were estimated 60%, 81.8% and 92%, respectively under selected conditions (PCB concentration,12 mg L−1; pH, 7; ratio of sulfite/TiO2, 1:1; reaction time, 60 min).The 98.5% degradation of PCBs was obtained when both oxidative and reductive agents (UST) were applied simultaneously. Also, as the kinetic information, value of robs for UST was 27.33, 16.4, 9.84, 8.2, 2.23 and 1.44 times than that of the sulfite, TiO2, TiO2-sulfite, UV alone, US and UT, respectively. Also, values of energy consumption for UV alone, US, UT and UST were calculated 426, 115.13, 74.4 and 51.95 kW h m-3, respectively. The maximum mineralization percentage for UST was obtained 70.92% under selected conditions. The results indicated addition of nitrate and t-But (which are strong scavengers of (eaq- and SO3-) and (O2- and OH radicals, respectively) simultaneously, significantly was diminished the degradation performance from 98.5% (in the absence of scavengers) to 70% (in the presence of nitrate and t-But together); it clearly proved reductive (SO3-and eaq- radicals) and oxidative (OH and O2- radicals) agents plays a noticeable role in the PCB degradation.