Bioremediation of Petroleum and Radiological Contaminate Soil Using an Ex Situ Bioreactor

Abstract

The Savannah River Site (SRS), a Department of Energy facility, generated non-hazardous petroleum and radiological co-contaminated soils that did not have a disposal pathway. The purpose of this project was to generate treatment data and test the hypothesis that an engineered biological process could safely and efficiently remove petroleum co-contamination from radiological contaminated soil. Demonstration of the treatment would allow the soils to be disposed as low-level radiological materials.

Although radiation and radiological contamination may, depending on the type and level, impact microbial activity and growth, the impact of low levels of radiation were not expected to impact the biodegradation of petroleum contaminated soils. Important parameters identified for successful biological treatment included oxygen mass transfer, bioavailability, temperature, microbiological capabilities, nutrients, and moisture. System design was based on a bioventing approach to control the supply of oxygen (air) based on petroleum contamination levels and type of soil being treated.

Before bioremediation began, a bioreactor system was permitted, designed, constructed, and tested. An operating permit was obtained from SCDHEC, as were approvals required by the SRS. The design was based on bioventing principles and used a modified prefabricated skid-pan, which was constructed by SRNL.

System operation included formulating a test plan, developing and using system sampling and monitoring methods, loading the system, starting up operations, obtaining results, modifying operation, and final disposal of the soil after the bioremediation goal was achieved.

The PRCS bioreactor operated for 22 months in various configurations treating the contaminated soil to a final TPH concentration of 45 mg/kg. During operation, degradation of over 20,000 mg/kg of waste was accounted for through monitoring of carbon dioxide levels in the effluent. System operation worked best when soil temperatures were above 15 ?nd the pumps were operated continuously. The low level radiological contaminated soil was disposed in an engineered trench at SRS that accepts this type of waste. The project demonstrated that co-contaminated soils could be treated biologically to remove petroleum contamination to levels below 100 mg/kg while protecting workers and the environment from radiological contamination.