Low Temperature Ex Situ Bioremediation of Hydrocarbon Contaminated Soils

Many oil degrading bacteria thrive within the mesophilic temperature range, between 20°C and 40°C; bioremediation practitioners view this as the optimal temperature range for microbially driven hydrocarbon remediation. Environmental managers generally halt active bioremediation projects during the winter months as microbial activity is thought to be insignificant and not cost effective. Recent research has cast some doubt on this assumption. In temperate climates there is a sizeable proportion of a soil’s biomass that consists of cold adapted bacteria, that can efficiently degrade hydrocarbon at temperatures around 5°C. When properly stimulated these psychrophiles and psychrotrophs can continue to remove contaminants from soil at temperatures just above the freezing point of water. Considering Southern Alberta’s regular Chinook cycles, low temperature bioremediation holds great promise. In this paper, recent results are presented from the cold climate bioremediation research being carried out in the University of Calgary’s Engineering for the Environment program. Approximately 300 m of clay-sand subsoil, moderately contaminated with diesel and crude oil (1395 3130 ppm), was transferred from an industrial area northeast of Calgary to an engineered treatment pad at the Shepard Landfill. A treatment pile was constructed for the soil and arranged into four treatment cells (one control and three test). The control cell was left untouched to provide a baseline against which the test cells could be compared. The first test cell was mechanically aerated on a monthly basis to release entrapped volatiles and oxygenate the soil. The second test cell was provided with optimal nutrient, moisture and oxygenation regimes. The final test cell was treated the same as cell two, but was not aerated. Total petroleum hydrocarbon (TPH) concentrations at the site were monitored for six months from January to June. Hydrocarbon concentrations were determined gravimetrically and the concentration of specific hydrocarbon fractions by gas chromatography (flame ionization detection). Microbial enumeration was carried out using most probable number (MPN) methodology. Results showed that under optimized conditions alkane based hydrocarbon contaminants can be significantly reduced (>60% TPH reduction) during cold temperature periods (January – May).