In situ bioremediation of Fenton's reaction-treated oil spill site, with a soil inoculum, slow release additives, and methyl-ß-cyclodextrin.

A residential lot impacted by spills from a leaking light heating oil tank was treated with a combination of chemical oxidation and bioremediation to avoid technically challenging excavation. The tank left emptied in the ground was used for slow infiltration of the remediation additives to the low permeability, clayey soil. First, hydrogen peroxide and citrate chelate was added for Fenton's reaction-based chemical oxidation, resulting in a ca. 50% reduction from the initial 25,000 mg/kg average oil concentration in the soil below the tank. Part of this was likely achieved through mobilization of oily soil into the tank, which was beneficial in regards to the following biological treatment. By first adding live bacteria in a soil inoculum, and then oxygen and nutrients in different forms, an approximately 90% average reduction was achieved. To further enhance the effect, methyl-ß-cyclodextrin surfactant (CD) was added, resulting finally in a 98% reduction from the initial average level. The applicability of the surfactant was based on laboratory-scale tests demonstrating that CD promoted oil degradation and, unlike pine soap, was not utilized by the bacteria as a carbon source, and thus inhibiting degradation of oils regardless of the positive effect on biological activity. The effect of CD on water solubility for different hydrocarbon fractions was tested to serve as the basis for risk assessment requirements for authorizing the use of the surfactant at the site.

Electrokinetically enhanced bioremediation of creosote-contaminated soil: laboratory and field studies.

Creosote is a toxic and carcinogenic substance used in wood impregnation. Approximately 1,200 sites in Finland are contaminated with creosote. This study examined the possibility of enhancing bioremediation of creosote-contaminated soil with a combination of electric heating and infiltration and electrokinetic introduction of oxygenated, nutrient-rich liquid. Preliminary tests were performed in the laboratory, and a pilot test was conducted in situ at a creosote-contaminated former wood impregnation plant in Eastern Finland. Wood preservation practices at the plant were discontinued in 1989, but the soil and the groundwater in the area are still highly contaminated. The laboratory tests were mainly performed as a methodological test aiming for upscaling. The soils used in these tests were a highly polluted soil from a marsh next to the impregnation plant and a less polluted soil near the base of the impregnation building. The laboratory test showed that the relative degradation was significantly higher in high initial contaminant concentrations than with low initial concentrations. During the first 7 weeks, PAH-concentrations decreased by 68% in the marsh soil compared with a 51% reduction in the building soil. The field test was performed to a ca. 100 m3 soil section next to the former impregnation building. Nutrient and oxygen levels in the soils were elevated by hydraulic and electrokinetic pumping of urea and phosphate amended, aerated water into the soil. The DC current introduced into the soil raised the temperature from the ambient ca. 6 degrees C up to between 16 and 50 degrees C. Total PAH concentrations decreased by 50-80% during 3 months of treatment while mineral oil concentrations decreased approximately 30%. Electrokinetically enhanced in situ - bioremediation, which also significantly raised the soil temperature, proved to be a promising method to remediate creosote-contaminated soils.