Bioremediation of petroleum hydrocarbon contaminated soil

Abstract

The bioremediation of petroleum contaminated soil in large-scale treatment units was studied in conjunction with Sybron Chemicals Inc., Salem, VA. The soil had been previously contaminated and was spiked with additional petroleum. Water with different characteristics was circulated through the soil in order to evaluate the effect of nutrient enhanced treatment without and with addition of two inoculation materials - Sybron’s ABR Hydrocarbon Degraders and Rhodococcus sp. - on the rate of hydrocarbon degradation. Treatment units without nutrients and introduced organisms served as controls. Total petroleum hydrocarbon concentrations (TPH) were monitored using two alternative analytical methods, infrared spectrophotometry and gas chromatography. The results of the field study and different laboratory experiments, a radiotracer flask assay, static soil microcosms, and soil columns were compared. While nutrient addition did enhance biodegradation, the addition of autochthonous organisms was not found to accelerate hydrocarbon degradation rates in the previously contaminated soil. A significant decline of surface tension in the circulated water after inoculation with Rhodococcus, was thought to be due to microbial production of surfactants, but did not increase TPH degradation. The radiotracer technique and microcosm study confirmed these results. The soil column study indicated that the rapid degradation of soluble and slower degradation of less soluble hydrocarbons occurred in two subsequent phases with approximately zero order rates. Typical degradation rates for the more soluble or degradable petroleum hydrocarbons were approximately 40 ppm/week and for the less soluble and degradable compounds 10 ppm/week. Microcosms were found to successfully predict the degradation rates of the soluble hydrocarbons, while the soil columns simulated degradation of the less soluble hydrocarbons best. The analysis of soil extracts for petroleum hydrocarbon concentrations with infrared spectrophotometry was found to be defective.