Anaerobic biodegradation of toluene coupled to sulfate reduction in oil-contaminated soils: Optimum environmental conditions for field applications

Degradation characteristics of toluene in enrichment culture were investigated in soil microcosms study and the optimum environmental conditions for anaerobic degradation of toluene coupled with sulfate reduction were determined for field site applications. Anaerobic sulfate-reducing bacteria were enriched from oil contaminated soil samples with toluene. Enriched consortia degraded toluene with sulfate as a terminal electron acceptor. The average degradation rate of toluene in enriched consortia ranged from 0.08 to 0.1 μmol g^-1 day^-1. Toluene degradation under sulfate-reducing condition was inhibited in the presence of molybdate alone or together with nitrate or fumarate, indicating that toluene is degraded directly by sulfate-reducing bacteria. Effects of initial toluene concentration, pH, temperature, and other hydrocarbons on toluene degradation were investigated. There is a trend of increasing rate of toluene degradation with increasing the initial mass up to 94 μmol of toluene. Toluene degradation did not affected by the presence of ethylbenzene and xylene, as a while, toluene was degraded in a slower rate in the presence of benzene. The sulfate-reducing bacteria in the enriched culture showed higher microbial activity at neutral (pH 6-8) and medium temperature (30-37°C) environments.