Microbiological and physicochemical studies of spent lubricating oil contaminated soil amended with wood ash

Microbiological and physicochemical studies of spent lubricating oil contaminated soil amended with wood ash (10% amendment level) were carried out for a period of 56 days. The aim of this study was to evaluate the effect of wood ash in conditioning spent lubricating oil contaminated soil. Serial dilution and pour plate methods were used in enumerating microbial growth. The pH, nitrate, moisture, phosphorus, organic matter content were also determined. The heterotrophic bacteria count ranged from 1.0×104 to 2.1×104 cfu/g for the oil free soil (OFS), 1.3×104 to 2.7×104 cfu/g for the polluted control soil (PCS) and 2.1×104 to 2.3×104 cfu/g for the amended soil (AS) while the fungal count ranged from 4.0×103 to 4.7×104 cfu/g for OFS, 4.0×103 to 8.2×104 cfu/g for PCS and 4.0×103 to 10.8×104 cfu/g for AS. Higher microbial counts were found on the PCS and AS compared to the OFS. There were no significant differences at 5% probability level between the treatments. The organisms isolated were species of Bacillus, Staphylococcus, Micrococcus, Aspergillus, Mucor, Penicillium and Saccharomyces. There were no significant differences (p>0.05) in the moisture content, nitrate, organic matter content and electrical conductivity. However, there were significant differences in the pH, organic carbon and phosphorus contents of the soil samples at 5% probability level. The results obtained in this study demonstrate the potential of wood ash to considerably increase the organic carbon, phosphorus and pH of the soil to slightly alkaline condition which favours the biodegradation of the spent lubricating oil contaminated soil.