Effects of chlorophenols and nitrophenols on the kinetics of propionate degradation in sulfate reducing anaerobic systems

The ability of sulfate-reducing bacteria (SRB)to effectively degrade several substituted and non-substituted aromatic and aliphatic compounds offers a promising alternative for the treatment of sulfate-containing industrial wastewaters and landfill leachates. For the design of sulfate-reducing anaerobic treatment systems for such wastewaters, it is important to determine the effects of toxicants on the kinetics of sulfate-reducing and methanogenic reactions. Batch kinetic experiments were conducted in the presence and absence of selected organic toxicants with a sulfate-reducing propionate enrichment culture. Fourteen chlorophenols and four nitrophenols were selected for this study. Toxicity due to dichlorophenols and trichlorophenols to both propionate and acetate degradation was dependent on the substitution position of chlorine atoms on the benzene ring. Among the dichlorophenols, 2,3-dichlorophenol and 2,6-dichlorophenol were the least toxic and 3,5-dichlorophenol was the most toxic. Among the trichlorophenols, 2,3,5-trichlorophenol and 2,4,5-trichlorophenol were more toxic as compared to 2,3,6-trichlorophenol and 2,4,6-trichlorophenol. Toxicity due to the mononitrophenols was also dependent on the substitution position showing 4-nitrophenol as the least toxic. All of the selected nitrophenols were more toxic to acetate utilization by methanogens than propionate utilization by the SRB.