Abstract

The biodegradation of the potent carcinogen, benzo[a]pyrene (BaP), and other priority pollutants was investigated in un-weathered coal tar contaminated soil over a period of 150 days. Results from the laboratory microcosm experiments showed that after 60 days, the concentrations of BaP were significantly reduced by 81%, in the biodiesel amended samples compared to the 26% and 34% depletion in the control and nutrient-only amended microcosms, respectively. The 3-ring PAH anthracene was also almost completely biodegraded in the presence of biodiesel. However, phenanthrene degradation was significantly inhibited in these samples as only 3% reduction occurred as opposed to the 80% depletion observed in the control. A stepwise treatment approach conducted on the coal tar spiked soil also revealed a higher reduction in BaP (98%) in the biodiesel amended microcosms compared to the control (29%) and further enhanced the depletion of phenanthrene by 51% after 60 days of adding biodiesel to soil initially treated with nutrients. Toxicity assays showed that biodiesel amended microcosms stimulated phosphatase enzyme activity and exhibited a lower toxic response to Microtox Vibrio fischeri. Overall, the pattern observed in the removal of the PAHs using biodiesel, suggests the co-metabolic action of ligninolytic fungi, probably via lignin peroxidases, as also evidenced from the visible growth of moulds after 14 days of amendment. The enhanced removal of carcinogenic PAH and the reduced toxicity observed in soil after biodiesel amendment, indicates that this bioremediation technique has potential for full scale field trials.

Keywords: Biodiesel; Biodegradation; Coal tar; Toxicity; Soil; Nutrient; Benzo(a)pyrene