IN SITU BIOREMEDIATION OF HYDROCARBON-CONTAMINATED SOIL BY AUTOCHTHONOUS MICROORGANISMS: A FULL-SCALE PROJECT

摘要

Leaks of petroleum compounds from underground storage tanks (USTs) containing gasoline, diesel fuel and other oils are a serious and increasingly prevalent problem in Argentina. A Full-Scale project was conducted to bioremediate hydrocarboncontaminated soils at a muffler factory in Rosario, Argentina. Extensive soil contamination was discovered in 1997. This contamination was caused by oil leaks from two USTs which had not been used since the mid-1980’s. The area of impacted soil was estimated to be 40 m x 3 m, and 3 m in depth. The affected soil had TPH concentrations as high as 60,000 mg/Kg. The groundwater was not contaminated by the oil. Following the removal of the USTs, soil samples were collected from different depths to determine the contaminant distribution. Well N°1 (Site 1) was filled with contaminated soil mixed with exogenous microorganisms. Well N°2 (Site 2) was filled only with contaminated soil. The exogenous microorganisms used were isolated from the same contaminated soil and cultivated in the laboratory before inoculation. The contaminated and uncontaminated soils added were both characterized as sandy loam (texture: 61% sand, 22% silt, 17% clay), the mean soil porosity was 0.42 and the mean unit weight was 1,580 Kg/m3. The operations began in October 1998 and concluded in August 1999. The operations included tilling and irrigation. Moisture content, pH, TPH, total aerobic heterotrophic bacteria and hydrocarbon-degrading microorganisms were measured monthly during the project. The results showed that Site 1 (which contained exogenous microorganisms) achieved a significantly higher percentage of TPH removal than Site 2. At the end of the project, the removal efficiency was 99% for Site 1 and 74% for Site 2. The addition of autochthonous microorganisms to a hydrocarbon-contaminated soil improves biodegradation.