Effect of Agro-Waste on Bioremediation of Soil Polluted with Spent Hydrocarbon in Keffi, Nasarawa State, Nigeria

Petroleum hydrocarbon is a major environmental pollutant throughout the world. This study was aimed at the effect of agro-wastes on bioremediation of soil polluted with spent hydrocarbon in Keffi. Hydrocarbon contaminated soils were collected from three (3) different auto mechanic workshops in Keffi, Nasarawa State Nigeria. The agro wastes used as stimulants were corncobs, fruits peels and melon shells. The hydrocarbon utilization was determined using gravimetric analysis. The hydrocarbon utilization bacteria were isolated and identified using standard microbiological method. The hydrogen ions (pH) of the contaminated soil sample were 4.5. pH of corncobs (CB) was 6.2, melon shells (MS) was 5.6 and fruits peels (FP) was 7.6. The value of total nitrogen for contaminated soil was 0.45 %, when amended with CB was 6.2%, MS was 1.26% and FP was 3.56%. Organic carbon in contaminated soil prior to study was 5.80 %, when amended with CB was 9.03%, MS was 7.55% and FP was 10.12%. The Phosphorous in contaminated soil was 8.41 mg/kg, when amended with CB was 13.40 mg/kg, MS was11.82mg/kg and FP was 15.61 mg/kg. Effect of time in reduction of hydrocarbon from contaminated soil amended with CB recorded highest after 40days (44.98 mg/kg) and the least (10.31 mg/kg) after 10days. Contaminated soil amended with CB the highest reduction was at 30 ℃ (48.92 mg/kg) and the least was at 35℃ (19.21mg/kg). From FP the highest reduction was at 30℃ (48.04 mg/kg). The highest degrading bacteria count was recorded from Keffi garage mechanic workshop (4.04 x106 cfu g/ml) and the lowest was from pyanko road mechanic workshop (1.18 x106 cfu g/ml). The highest bacteria isolated from none amended contaminated soil was Flavobacterium sp (33.3 %) and the lowest was Bacillus subtilis and Proteus sp (33.3%). From amended soil with CB the highest were Corynebacteria spp and Flavobacterium sp (100%) and the lowest were Bacillus subtilis, Pseudomonas flourescens, and Proteus sp (66.6%). From contaminated soil amended with MS the highest bacteria isolated were Flavobacterium sp and Corynebacteria sp (33.3%) and the lowest were Pseudomonas flourescens and Proteus sp (33.3 %). From contaminated soil amended with FP the highest bacteria isolated were Pseudomonas flourescens and Proteus sp (100%) and the lowest were Bacillus subtilis, Flavobacterium sp and Corynebacteria sp (66.6%). It is recommended that the environmental agencies in the country give consideration to agricultural waste products for bioremediation of hydrocarbon polluted soil in Nigeria.