A mesocasm study of enhanced anaerobic biodegradation of petroleum hydrocarbons in groundwater

Under certain conditions, Natural Attenuation (NA) processes can act to reduce the mass, toxicity, mobility, volume or concentrations of contaminants in soil or groundwater within a reasonable time frame. NA processes are considered to be a more cost-effective remediation approach than engineered processes. However, the rates of biodegradation in cold regions are slower and occasionally the processes are nutrient or Terminal Electron Acceptor (TEA) limited. These limitations may make NA less viable due to slower rates of biological activity. This paper discusses the results of a mesocasm study conducted in laboratory-controlled conditions to investigate the TEA and nutrient enhanced anaerobic biodegradation of petroleum hydrocarbons in groundwater from two sites in Alberta. Target compounds for the study were BTEX and the CCME F1 fraction. Samples taken from the site were used to set up 11 L mesocasms with a water to soil ratio of 10:1 under anaerobic conditions. The samples were amended with nitrate and sulfate and then incubated. Sub-sampling was carried out once a month to monitor substrate consumption, TEA depletion and evolution of biogenic gases. Microbial enumeration and metabolite analysis were also done. No final conclusions could be drawn from the study, which had only been carried out for 6 months at the time that this paper was written. However, results to date have indicated that the method of mesocasms and sub-sampling are applicable to anaerobic biodegradation studies. In addition, nutrient supplementation appears to enhance nitrate and sulfate reduction. However, the TEA depletion was greater than expected and could not be explained by the substrate consumption. Results also indicated that the groundwater from site 1 was sulfate-limited, suggesting that sulfate amendment could enhance anaerobic biodegradation of CCME F1 petroleum hydrocarbons. Data from the ongoing study may provide additional insight to clarify processes in the mesocasms. 9 refs., 1 tab., 6 figs