Biostimulation of Crude Oil Contaminated Soil Using Soybean Waste

Abstract

The potential of soybean waste (SBW) in enhancing microbial breakdown of crude oil in soil was studied. The soybean waste contained 5.31% nitrogen and 33.2% crude protein while the soil used for the bioremediation study contained 1.89% organic matter, 1.10% organic carbon, 0.21% nitrogen and 0.08 ppm phosphorus. The textural composition of the soil was 76.58% sand, 8.28% silt, 15.16% clay and the soil was classified as sandy loam. The microbiological analysis revealed that aerobic heterotrophic bacteria counts in oil polluted soil amended with SBW ranged between 1.6×108 cfu/g and 8.9×108 cfu/g. These counts were higher than those of the unamended soil which ranged from 1.2×108 to 3.6×108 cfu/g. The crude oil utilizing bacteria counts ranged between 1.2×108 cfu/g and 5.3×102 cfu/g, while the fungi counts ranged between 2.0×102 cfu/g and 9.5×102 cfu/g. The crude oil utilizing bacteria identified in soil amended with SBW were species of Bacillus, Acinetobacter, and Pseudomonas and the fungi were species of Aspergillus, Mucor, and Cephalosporium. Amendment of the soil with SBW raised the exchangeable cations, nitrogen and phosphorus contents of the soil. Crude oil polluted soil amended with SBW also had higher amount of organic carbon than the unamended soil. The extent of crude oil degradation in oil polluted soil amended with 200 g SBW, 400 g SBW and in unamended soil were 54.6, 70.4% and 8.8% respectively after 28 days. The values were significantly different (P < 0.05). The results of this study suggest that soybean wastes are good enhancers of crude oil biodegradation in the soil and therefore, can be used in reclaiming crude oil polluted soil