Biostimulation of Oil Refinery Soils

Oil refinery contaminated soils usually contain carcinogenic products, including polycyclic aromatic hydrocarbons (PAHs), and therefore require treatment for environmental and human protection. Biostimulation is the modification of external factors affecting the performance of indigenous bacteria and it may be employed to enhance natural attenuation at contaminated sites. Contaminated soil samples, provided by Imperial Oil (Sarnia, Ontario), were analyzed using pyrosequencing to sequence DNA strains in order to identify types of bacterial genus found in the samples. Flavobactericeae and Marinobacter were the two most dominant genus found in the sample, both recorded with the ability to degrade PAHs. Favourable conditions and governing parameters such as water holding capacity, moisture content, pH, total organic carbon, phosphorous, nitrogen, and potentially toxic environments, including sulfate and metal concentrations, were quantified in two experiments. The first experiment was batch studies containing a water: soil ratio of 10:1 (100 mL water: 10 g of contaminated soil sample). A second batch study, containing 50 g of contaminated sample with 60% saturation, was employed to determine effects of temperature. Plasma optical emission spectroscopy, Kjeldahl Method (for nitrogen), Olsen method (for phosphorous), gas chromatograph (GC), GC/MS, and HPLC were used for the analysis of samples. Urea was added to the sample as the nitrogen source and di-ammonium phosphate was added as the source of phosphorous. A target organic carbon: nitrogen: phosphorous (C:N:P) ratio of 100:10:1 was maintained for bacterial health. The pH was observed to be in the range of 6-8 throughout both experiments, and the water holding capacity of the samples was 22.7 wt%. Metal concentrations were found to be too low to cause toxic conditions for bacteria growth. Results suggest that the bacteria may have been using PAHs as a carbon source