ENHANCING HYDROCARBON BIODEGRADATION RATE ON LANDFARMING USING EXOGENOUS MICROORGANISMS: A FIELD STUDY

摘要

A field study was conducted at a landfarming site belonging to the Petroleum Refinery San Lorenzo located in San Lorenzo City, Santa Fe Province, Argentina, to evaluate the effectiveness of added exogenous microorganisms. Two existing cells were used for the study (Cell 1 and Cell 2). The soil was characterized as sandy loam (texture: 56% sand, 18% silt, 26% clay), the mean soil porosity was 0.38, and the mean bulk density was 1,270 kg/m~3. Initial total hydrocarbon concentration in the soil averaged approximately 6% w/w, including saturates 51%, aromatics 12%, resins 12%, and asphaltenes 25%. In both cells, heavy metals were present: 23,000 mg/kg Fe; 90 mg/kg V; 348 mg/kg Ni; 44 mg/kg Pb; 55 mg/kg Cu; and 1.3 mg/kg Hg. Exogenous microorganisms (hydrocarbon degraders) were added (at the beginning of the study) to compare degradation rates in Cell 2 with those in Cell 1 in which indigenous microorganisms were allowed to develop. The exogenous microorganisms were isolated from the same landfarming area and were cultivated in the laboratory before inoculation. Landfarming operations began in September 1997 and concluded in August 1998. The operations in both cells included tilling and irrigation. Moisture content, pH, total hydrocarbons, total aerobic heterotrophic bacteria, and hydrocarbon-degrading microorganisms in each cell were determined monthly during the study. No fertilizers were applied in this study. Cell 2 (which contained exogenous microorganisms) achieved a higher percentage of total hydrocarbon removal than Cell 1. At the end of the study, the removal efficiency was 84% for Cell 2, but only 49% for Cell 1. The results of the field study showed that bioaugmentation was effective, in spite of the presence of high concentrations of heavy metals and the fact that fertilizers were not used.