Bioremediation of hydrocarbon contaminated soil using selected organic wastes

Traditionally soil remediation has been known to be among the most expensive treatments in the world. Thus, various strategies have been opted to investigate the most cost-effective solution to deal with contaminated sites. Among the highly potential approach is bioremediation since many studies have reported of its effectiveness in removing numerous pollutants from many contaminated sites. It mainly involved biostimulation where organic or inorganic components were introduced to enhance indigenous microbial growth that directly degrades the contaminants. This paper aims to identify potential organic wastes in enhancing the biodegradation of used lubricating oil in contaminated soil. To achieve the objective, sewage sludge and cow dung were selected as the organic components to be added individually into the 10% (w/w) used lubricant oil-contaminated soil. Each set up with 1.5kg of used lubricant oil-contaminated soil were added with 10% of the organic matter (sewage sludge or cow dung) and left for degradation for 98 days in plastic vessels. Periodic sampling of soil from each vessel was carried out at 14 days interval for total petroleum hydrocarbon analysis, and isolation and enumeration of bacteria. Results indicated that after 98 days of exposure to the organic matters, biodegradation of used lubricant in the soil were much higher than that of the control set-ups. Cow dung amended set-ups showed 94% biodegradation while sewage sludge amendment gave 82%, as compared to the control set-up (56%). This probably was due to the presence of additional nutrient in the organic matter amended soil which enhanced the indigenous microbes' degradation capabilities. As for the performance, the biodegradation rate of the two organic matters differed due to the differences in the nutrient content, particularly of available N and P. In addition, cow dung amended-soil was found to have improved soil physiochemical characteristics that enabled speedy adaption by the microbes to the contaminated soil. Statistical analysis indicated a significant difference at P<0.05. Based on the first order kinetics model, cow dung amended soil gave the highest biodegradation rate of 0.2086/day with used-lubricant half-life of 3.32 day. On the other hand, sewage sludge amended soil has a biodegradation rate of 0.149/day with used-lubricant half-life of 4.65 days. These biodegradation rates were significantly higher than that of the control soil (0.0915/day) and autoclaved soil (0.0309/day). As for the microbial counts, cow dung amended soil recorded (69-122) 10(7) CFU/g while sewage sludge amended soil recorded (63-96) 10(7) CFU/g. On the other hand the control soil recorded (52-73) 10(7) CFU/g. Again, the presence of available nutrients required by the microbes could be the contributing factor to the high distribution of microbes in the organic matter amended soil as compared to the control soil. In conclusion, cow dung and sewage sludge can be an effective organic amendment for the biodegradation of used lubricant contaminated soil. Both organic matters proved to enhance the multiplication of indigenous microbes thus enabling rapid biodegradation of the contaminant in the soil. (C) 2013 The Authors. Published by Elsevier B.V.