Photo-assisted degradation of 2, 4, 6-trichlorophenol by an advanced reduction process based on sulfite anion radical: Degradation, dechlorination and mineralization

This research was aimed at evaluating the performance UV only and sulfite-mediated photoreduction process (an advanced reduction process) in the degradation, dechlorination and mineralization of 2, 4, 6-trichlorophenol (TCP). Firstly efficiency of sulfite-mediated photoreduction (SMP) process in the degradation of TCP was investigated and obtained the complete degradation of TCP (250 mg L−1) under the selected conditions (pH, 7.0; [sulfite]/[TCP] = 3.13; UV irradiation, 87 μW cm−2 and dissolved oxygen (DO), 2 mg L−1) at 80 min whereas degradation rate of TCP by UV only was 73% at similar time. Investigate of degradation mechanism revealed the higher ability of sulfite radicals (SO3-) than eaq− and H in the reduction of TCP by the SMP process. In the second stage, UV only and SMP process efficiencies were investigated in the dechlorination of TCP. The dechlorination percentage (cleavage of CCl bonds) of TCP (250 mg L−1) for UV only and SMP process was 36 and 98% respectively. The contrary of TCP degradation process, investigation of reaction mechanism for TCP dechlorination process elucidated eaq− along with SO3- have important role in the dechlorination of TCP (although, the SO3- role was significant than the eaq−). In the next stage, mineralization of TCP using SMP process was evaluated by chemical oxygen demand (COD) and related result was 30.2%. The aromatic intermediates such as 2-chloro-1-benzoquinone, 2-hydroxy benzoquinone, 2-chlorophenol, benzene, 1, 3-cyclohexadiene and cyclohexene are identified by using LC-ESI/MS analysis.