Biodegradation of Spent Automobile Engine Oil in Soil Microcosms Amended with Cow Dung

Abstract

The discharge of spent engine oil in terrestrial and aquatic environments constitutes public health and socio-economic hazards. In this study, the potentials of organic waste (cow dung) amendments as biostimulating agents of the indigenous microflora for hydrocarbon biodegradation in soil microcosms deliberately contaminated with spent engine oil (5%v/w) was investigated for a period of 6 weeks. Physico-chemical and microbiological analysis of soil samples was determined using standard methods. A microcosm constructed consists of 8 trays containing 1kg of soil, artificially contaminated with 50ml of spent engine oil and treated with 50g, 100g and 150g of cow dung. Spent engine oil degradation was assessed gravimetrically at weekly interval and chromatographically after 6 weeks of biodegradation treatment. Results of the physico-chemical analysis showed that the pH of soil was 6.56 while nitrate, moisture content, phosphate and total organic content were 0.82mg/kg, 9.28%, 0.73mg/kg and 3.60mg/kg respectively. Microbiological analysis of the soil sample showed that the total heterotrophic bacteria were 3.6x106cfu/g, while total heterotrophic fungal and hydrocarbon utilizing bacteria (HUB) were 2.2x104cfu/g and 7.9 x104cfu/g respectively. The mean value of the total viable counts (TVC) population of hydrocarbon-utilizers was higher in biostimulated soil which ranged from (2.10x10⁵-5.30x10⁹cfu/g) compared with that of control (1.20x10⁵-3.10x10⁸cfu/g). Residual oil concentration showed a more remarkable decrease throughout the incubation period (0.400-0.259mg/g, 0.420-0.218mg/g and 0.410-0.220mg/g for treatments 1, 2 and 3 respectively) when compared to that of control which ranged from 0.400-0.304mg/g. At the end of 6 weeks of microcosms biodegradation studies, percentage degradations of the spent engine oil were 23.81%, 35.29%, 45.45% and 44.94% for CON, T1, T2 and T3 respectively. The result obtained from this study showed that cow dung can be effectively used as a biostimulant during bioremediation of spent engine oil polluted site to enhance biodegradation ability of the indigenous microbial population.