Anaerobic biodegradation of benzene, toluene, ethylbenzene and xylenes (BTEX) is a compelling alternative for in situ bioremediation in hydrocarbon plumes where oxygen is commonly in short supply. In anaerobic BTEX degradation, nitrate, sulfate or CO2 replace oxygen as an electron acceptor to support the metabolism of specialized BTEX degrading microorganisms; this is a major advantage as nitrate or sulfate are relatively easy to apply to groundwater compared to oxygen.
Over the past 2 years, SiREM, the University of Toronto (Elizabeth Edwards’ Lab) and industrial partner Federated Co-operatives Limited have performed more than 10 anaerobic BTEX treatability studies under a Genome Canada project*. These 12 to 14-month laboratory studies were performed using groundwater and geologic materials from sites located in Ontario, Western Canada, and the USA and focused primarily on the potential for anaerobic benzene or BTEX
degradation under natural and enhanced conditions.
Ontario BTEX Site Treatability Case Study
One study conducted under the project was for a site located in Ontario, Canada contaminated with BTEX at concentrations as high as 6 mg/L. Amendments included the addition of nitrate or sulfate and the benzene degrading bioaugmentation culture “DGG-1” which contains a benzene degrading Deltaproteobacteria called ORM-2, that functions under sulfate reducing or methanogenic conditions. Initially site geologic materials tested negative for ORM-2 (Gene-Trac® ORM-2) but were trace positive for the benzene degraders that function under nitrate degrading conditions based on benzene carboxylase and Peptococcaceae detection (Gene-Trac® abcA/Pepto- ben). This suggested that nitrate biostimulation or the addition of sulfate and bioaugmentation with the DGG-1 culture may be a viable remediation strategy.
The study demonstrated that all BTEX compounds could be degraded anaerobically under methanogenic and bioaugmented conditions,
specific findings included:
- Degradation of all compounds, except naphthalene, was observed with nitrate amendment when the abundance of benzene degrading Peptococcaceae bacteria increased.
- Sulfate addition alone stimulated degradation of only toluene and xylenes.
- Bioaugmentation with the DGG-1 culture, with or without sulfate addition, accelerated benzene degradation.
Overall the study indicated that biostimulation with nitrate was effective at enhancing biodegradation of all BTEX compounds and bioaugmentation with DGG-1 accelerated benzene degradation. These results illuminate a path forward for in situ remediation at the site. The extensive treatability testing under the research project continues to contribute to a greater understanding of the potential challenges and optimal conditions associated with anaerobic BTEX degradation including expected degradation rates, the range of geochemistry under which the process is viable, the ability to degrade mixtures, the most effective use of amendments and the need for bioaugmentation. Sandra Dworatzek, who manages treatability services at SiREM and is the user GAPP project lead says ….
“The opportunity to participate in such an extensive program of treatability testing for petroleum hydrocarbons has helped to further our understanding of anaerobic BTEX degradation and is laying a solid foundation for upcoming field pilot tests.”
The ability to optimize anaerobic BTEX pathways will be a big step forward in our ability to cost effectively deal with hydrocarbon plumes which are as common as gas stations. Treatability testing is leading the way to field pilots and full-scale remediation efforts in the near future.
* This research is supported under a Genomic Applications Partnership Program (GAPP) grant funded by Genome Canada, Ontario Genomics, Ontario Ministry of Research and Innovation, Mitacs, Federated Cooperatives Limited and SiREM.
Funding for this project provided in part by: