Bioremediation of Petroleum-Hydrocarbon Contaminated Groundwater under Sulfate-Reducing Conditions: Effectiveness and Mechanism Study

Groundwater at many existing or former industrial areas and underground storage tank sites is contaminated by petroleum hydrocarbons. In this study, a column experiment was applied to evaluate the effectiveness and mechanisms of sulfate reduction processes on the bioremediation of benzene, toluene, and methyl-t-butyl ether (MTBE) contaminated groundwater. Simulated anaerobic groundwater containing benzene, toluene, and MTBE (average concentration = 20mg/L) was pumped into the system at a flow rate of 0.36mL/min. Sulfate (used as the electron acceptor) was injected into the system to activate the sulfate-reducing process. Anaerobic sludge collected from an anaerobic basin of an industrial wastewater treatment plant was inoculated into the system to enhance the sulfate reduction rate. Up to 92, 65, and 45% of toluene, benzene, and MTBE removal efficiencies were observed with the first-order decay rate of 34, 1.8, and 11/d, respectively. Results indicate that toluene is more biodegradable under sulfate-reducing conditions compared to benzene and MTBE, and 0.7g/L of sulfate consumption was observed during the biodegradation process. The occurrence of sulfate reduction can be confirmed by the increased sulfide (increased from 7-9 to 340-520mg/L) and ferrous iron (increased from <0.1 to 52mg/L, then dropped to 0.14mg/L attributable to the formation of iron sulfide) concentrations. In the latter part of this study, accumulation of hydrogen sulfide caused the microbial inhibition, and thus, decreased contaminant removal efficiencies were observed. The microbial communities were characterized by 16S rRNA-based denaturing gradient gel electrophoresis (DGGE) profiling for soils in the system. Results show that sulfate addition could result in the enhancement of sulfate reducer growth, and thus, sulfate reduction becomes the dominant biodegradation process. A total of 39 different petroleum-hydrocarbon degrading bacteria were observed under the sulfate-reducing conditions. Results indicate that the sulfate reduction has the potential to be developed into a practically and economically acceptable technology to remediate petroleum-hydrocarbon contaminated groundwater. (C) 2015 American Society of Civil Engineers.