The potential for reductive dehalogenation of chlorinated phenol in a sulphidogenic environment in in situ enhanced biodegradation

Abstract

An investigation of the reductive dechlorination of 2, 4, 6-trichlorophenol (2, 4, 6-TCP) under sulphate-reducing conditions was made. Sulphate-reducing and dechloro-respiring activities were studied in a mixed microbial population operated in batch-fed as well as continuous pine chip-packed fluidised bed reactors. Results showed that reductive dechlorination of 2, 4, 6-TCP by the dechloro-respiring bacteria may be indirectly stimulated by the fermentative activity of the sulphate-reducing population affected by sulphate and lactate concentrations. Sulphate was administered in excess (900 mg·ℓ-1) and limiting (110 mg·ℓ-1) concentrations. At these concentrations, SO42- was available in quantities sufficient and lower than that required to bring about consumption of lactate. Transformation to 2,4-dichlorophenol (2,4-DCP), 4-chlorophenol (4-CP) and phenol was enhanced in sulphate-limiting conditions with average 47.7% TCP reduction compared to 11.6% in sulphate-enriched administered reactors. The potential application requirements for dechlorination under sulphate-reducing conditions for in situ biodegradation are considered. The input electron donor: SO42- ratio is manipulated to effect accelerated dechlorination rates for chlorinated organic compound-contaminated soil/groundwater bioremediation applications where oxygen is frequently limited.