The effects of freezing and thawing on the bioremediation of a diesel fuel contaminated soil
Studies have found that under constant environmental conditions, the rate of biodegradation of petroleum hydrocarbons decreases with time and may become negligible after a period. This decrease in the availability of hydrocarbons for biodegradation can be attributed to the diffusion of the hydrocarbons into soil micropores, the partitioning of the hydrocarbons into soil organic matter, strong surface adsorption or a combination of these processes. Studies have also shown that naturally occurring freeze-thaw cycles act to disrupt soil aggregates to physically change the soil's structure. This study investigated the effects of freeze-thaw cycles on the biodegradation rates of hydrocarbon contaminated soils. A diesel fuel contaminated soil was bioremediated in bench-scale reactors until respiration monitoring indicated a decrease in microbial activity. Designated reactors were then subject to 1, 3, 6 and 9 freeze-thaw cycles. The results indicated an increase in the microbial activity in the freeze-thaw treated reactors, while the microbial activity in the control reactors decreased over the same period of time. The results also indicated that microbial activity increased with increasing numbers of freeze-thaw cycles.