Biodegradation of Petroleum Hydrocarbons under Nitrate- and Sulfate-Reducing Conditions: Bench and Field Results

摘要

Petroleum hydrocarbons (HCs) were discovered in groundwater at the Minnesota Air National Guard facility (Site) in Duluth, Minnesota. A bench-scale treatability study evaluated the effectiveness of sulfate alone or combined nitrate and sulfate reduction for the biodegradation of site HCs (benzene, toluene, ethylbenzene, and total xylenes [BTEX], gasoline range organics [GRO] and diesel range organics [DRO]). In the sulfate and nitrate amended treatments, BTEX was degraded within eight weeks of the initiation of the study. No GRO or DRO were detected at week 13 in the nitrate and sulfate amended treatment bottles. In treatments where only sulfate was added, benzene, DRO and GRO lingered past week 13 of the study. All treatment bottles were respiked with HCs at week 13, and the pattern of complete HC degradation in the nitrate and sulfate amended treatment was repeated within the next 13 weeks. Based on these results, a field scale pilot test was conducted in the fall of 2006. The nitrate and sulfate was delivered in solution using a patented Wavefront? pressure pulse technology (PPT) because of the fine-grained materials comprising the shallow aquifer at these sites, A comparison of standard geoprobe injection and PPT methods was inconclusive due to development of preferential pathways during injection; however, a maximum radius of influence of 20 feet was reached using each of the methods. The first monitoring event was conducted one month after amendment injection and showed decreases in the groundwater concentrations of HC and lingering concentrations of sulfate. The pilot test was conducted during the coldest months of the year; monitoring will continue into August 2007. It is expected that the results will improve with more temperate conditions.