Bioremediation of complex chlorinated-solvent impacted groundwater.

Enhanced in situ bioremediation is a widely adopted and sustainable means of remediating chlorinated contaminant impacted groundwater utilizing organohalide respiring bacteria. These bacteria utilize chlorinated compounds as terminal electron acceptors to harvest energy, producing partially or fully dechlorinated end products. A barrier to successful remediation utilizing organohalide respiring bacteria is the impact of environmental factors which may be toxic or otherwise inhibitory towards these organisms or their respiration pathways, particularly in sites with complex contaminant profiles and heterogeneous geochemistry. In this study, groundwater from two regions of a heavily and mixed chlorinated solvent impacted site in Sydney, Australia with minimal historical evidence of natural attenuation was used to establish bench-scale microcosms for identification of factors that modulate successful bioremediation. The results of this study demonstrate that the success of enhanced bioremediation is minimally impacted by initial bacterial abundance with significant degradation of chlorinated hydrocarbons detected in microcosms with as low as 83 16S rRNA gene copies/mL following enhanced bioremediation, sulfate concentrations exceeding 71 mg/L may preferentially stimulate sulfate reducing bacteria, while chlorinated hydrocarbon concentration and composition remain the most inhibitory factors limiting bioremediation success.