Advances in Anaerobic Bioremediation of Benzene
Widespread use of petroleum products has resulted in contamination with BTEX compounds at numerous sites. BTEX compounds, which are the most soluble of petroleum hydrocarbons, can readily biodegrade under aerobic conditions, however where anaerobic conditions prevail, natural attenuation of BTEX has also been observed. Most often, under anaerobic conditions, benzene is observed to persist, due to its recalcitrance to degradation and can become a regulatory driver for remediation.
Several benzene degrading cultures have been identified including a methanogenic benzene enrichment culture (DGG-B), developed at the University of Toronto. DGG-B transforms benzene and produces methane and the key benzene degrader, Deltaproteobacteria ORM2, has been identified. This culture also degrades benzene under sulfate reducing conditions. Recent research efforts have been undertaken to determine 1) whether bioaugmentation with the DGG-B culture is an effective remedy for benzene contaminated sites; 2) if the presence of benzene degrading biomarkers can be correlated to in situ biodegradation activity and 3) if scale up of the culture to volumes sufficient for field pilot testing application is feasible.
Numerous anaerobic treatability studies have been conducted using site materials impacted with petroleum hydrocarbons. The time frame for these treatability studies ranged from 8 to 14 months. Degradation of BTEX was monitored with and without DGG-B bioaugmentation and under various electron acceptor conditions. The results to date indicate that bioaugmentation with the DGG-B culture was able to accelerate benzene degradation under methanogenic or sulfate-reducing conditions, while in one case, no benzene degradation was observed despite bioaugmentation.
Samples from the original groundwater materials, as well as microcosm samples were taken, to quantify the potential benzene degraders via quantitative PCR testing. The results indicated that increases in Deltaproteobacteria ORM2, the benzene degrader in DGG-B, were corelated with benzene degradation. Also, the putative benzene carboxylase gene (abcA) known to be related to a Peptococcaceae sp., that degrades benzene under nitrate reducing conditions, was detected by qPCR in two groundwater samples. In microcosms where benzene carboxylase was detected, benzene degraded intrinsically, although at much slower rates compared to the bioaugmented microcosms.
Results from ongoing treatability studies will be presented to provide insights into the performance of the DGG-B bioaugmentation culture at a range of petroleum hydrocarbon contaminated sites, as well as into the correlation between the presence of benzene degradation molecular biomarkers and in situ biodegradation.