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 s everal substituted and non-substituted aromatic and aliphatic compound s offers a promising alternative for the treatment of sulfate-containi ng industrial wastewaters and landfill leachates. For the design of su lfate-reducing anaerobic treatment systems for such wastewaters, it is important to determine the effects of toxicants on the kinetics of su lfate-reducing and methanogenic reactions. Batch kinetic experiments w ere conducted in the presence and absence of selected organic toxicant s with a sulfate-reducing propionate enrichment culture. Fourteen chlo rophenols and four nitrophenols were selected for this study. Toxicity due to dichlorophenols and trichlorophenols to both propionate and ac etate degradation was dependent on the substitution position of chlori ne atoms on the benzene ring. Among the dichlorophenols, 2,3-dichlorop henol and 2,6-dichlorophenol were the least toxic and 3,5-dichlorophen ol was the most toxic. Among the trichlorophenols, 2,3,5-trichlorophen ol and 2,4,5-trichlorophenol were more toxic as compared to 2,3,6-tric hlorophenol and 2,4,6-trichlorophenol. Toxicity due to the mononitroph enols was also dependent on the substitution position showing 4-nitrop henol as the least toxic. All of the selected nitrophenols were more t oxic to acetate utilization by methanogens than propionate utilization by the SRB.