Toxicity and reductive dechlorination of chlorophenols in anaerobic propionate systems
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Description
The fate of four trichlorophenols (TCP), six dichlorophenols (DCP), and three monochlorophenols (CP), were studied in anaerobic propionate enrichment systems. TCPs were more toxic than DCPs and CPs; 2,4,5-TCP was the most toxic compound to the propionate utilizers among the thirteen chlorophenols studied in this research. Most chlorophenols were reductively dechlorinated to less chlorinated compounds. Dechlorination at the ortho position was observed most frequently. 2,3,6-TCP was dechlorinated to form 2,3-DCP, which was then transformed into 2-CP and phenol. 2,3,5-TCP produced 3,5-DCP and subsequently 3-CP and phenol. 2,4,5-TCP was dechlorinated to produce 3,4-DCP followed by 3-CP and phenol. 2,4,6-TCP was dechlorinated sequentially at the ortho positions to produce 2,4-DCP and 4-CP, which then produced phenol. The chlorine in the meta positions of 3,5-DCP, 2,3-DCP, 2,5-DCP were removed to produce 3-CP, 2-CP, and 2-CP, respectively. 2,4-DCP and 2,6-DCP were dechlorinated at the ortho position to form 4-CP and 2-CP, respectively. 3,4-DCP was dechlorinated to produce 3-CP. Phenol was also detected during degradation of 2,3-DCP, 2,6-DCP, 3,5-DCP, 2-CP, 3-CP, and 4-CP. The overall removal of the selected chlorophenols by anaerobic propionate enrichment systems were in the following order: 2,3,5-TCP $>$ 2,3,6-TCP $>$ 3,5-DCP $>$ 2,4-DCP $>$ 2-CP $>$ 3,4-DCP, 2,3-DCP, 2,5-DCP $>$ 3-CP $>$ 2,4,5-TCP $>$ 2,6-DCP $>$ 2,4,6-TCP $>$ 4-CP The objective of Part II study was to determine the toxic effects and degradation of pentachlorophenol (PCP) in the presence of zinc in anaerobic propionate systems. Anaerobic toxicity assays (ATA), batch kinetic studies, and biodegradation studies were performed using serum bottles. PCP inhibition was modeled using both uncompetitive and noncompetitive inhibition kinetic models with an inhibition coefficient, K$\rm\sb{I},$ of 0.06 mg/l. Zinc toxicity showed that the competitive inhibition model was the best-fit model with a K$\rm\sb{I}$ of 1.1 mg/l. A combined competitive-uncompetitive inhibition model was the best-fit model in the presence of both PCP and zinc for propionate degradation. In the biodegradation studies, PCP removals were 72, 64, and 54% with spiked PCP concentrations of 2, 3, and 5 mg/l, respectively. In the presence of zinc, the removal of 2 mg/l and 3 mg/l of PCP decreased to 60% and 53%, respectively. The intermediates of PCP degradation were 2,4,6-trichlorophenol, 2,4-dichlorophenol, 4-chlorophenol, 2,3,5-trichlorophenol, 3,5-dichlorophenol, and 3-chlorophenol; lower concentrations of these intermediates were observed in the presence of zinc