Photo-catalytic degradation of Trichlorophenol with UV/sulfite/ZnO process, simultaneous usage of homogeneous reductive and heterogeneous oxidative agents generator as a new approach of Advanced Oxidation/Reduction Processes (AO/RPs)

摘要

This study develops UV/Sulfite/ZnO (USZ) photoreactor, as a novel method of Advanced Oxidation/Reduction Processes (AORPs), and employs it for degradation, dechlorination and mineralization of 2, 4, 6-trichlorophenol (TCP) content of wastewaters. Degradation efficiency of the UV-only, UV/ZnO, UV/Sulfite and USZ processes were determined as 23.4%, 37.6%, 44.8% and 87.83% respectively, at 10 min reaction time, 50 mg L-1 TCP concentration and pH of 7. Findings indicated that TCP degrades completely within 15 min treatment of 50 mg L-1 initial TCP concentration. According to Molar ratio evaluations, 1:2:50 is the optimal Molar ratio of sulfite/ZnO/TCP in the USZ process. Analyzing effluents of the USZ reactor by liquid chromatography/mass spectroscopy after 5, 10 and 15 min reaction time revealed that TCP decomposes to ring-shaped compounds in less than 10 min and all TCP and its metabolites convert to linear compounds within 15 min reaction time. Also fourteen little fragments were identified in the degradation of TCP by USZ during 2.5 till 15 min of reaction time. Investigating kinetic of the process through a pseudo first-order model using 10 to 200 mg L-1 TCP over 1 to 15 min reaction time demonstrated that the observed rate constant (k(obs)) decreases from 0.3811 to 0.0824 min(-1) and the observed TCP degradation rate (r(obs)) increases from 3.811 to 16.48 mg L-1 min(-1) with increase of TCP concentration. Furthermore, electrical energy consumption (E-EO) of the USZ process was calculated with kinetic model 2.21 to 10.25 as 2.19 to 3.55 and with merit-figure model 4.94 to 12.39 kW h m(-3) from 10 to 200 mg L-1, respectively. In addition, the effect of co-existing water anions on degradation of 50 mg L-1 TCP was explored during 30 min processing. While 100% degradation was achieved in the absence of any anion, adding nitrate, as the most effective anion, decreased TCP degradation to 78.24%. The highest dechlorination was observed at sulfite/ZnO Molar ratio 1:2 and pH 11.0. Mineralization of TCP by USZ process was achieved 33.2% after 15 min of reaction.