BIOREMEDIATION OF CRUDE OIL CONTAMINATED SOIL USING AGROWASTE

Abstract

The two agro-waste (horse dung and unripe plantain peels) used as biostimulants for the bioremediation of crude oil contaminated soil are of biological origin and are practical and safe environmental remediation agents. Microbiological (Gram staining, Catalase test, Citrate test, Starch hydrolysis, Methyl Red test, Motility, Urease test and Sugar fermentation) and physicochemical analysis (pH, Organic matter, Phosphorous, Nitrogen, Cation exchange capacity, Moisture) of the agro-waste and soil (contaminated and uncontaminated soil) were assessed before and after remediation. The agro-wastes were introduced into crude oil contaminated soil in single and combination (10% and 20 % respectively). The treated samples were incubated for 56 days and characterized for their physicochemical properties, microbial counts (which was determined every 14th day) and total petroleum hydrocarbon which was determined before and after the treatments. There was decrease in pH (6.67 to 4.10), organic carbon (15.53 to 6.07 %) and an increase in total phosphorous (10.06 to 15.30 mgkg-1) and nitrogen (0.29 to 4.72 %) of the oil contaminated soil remediated with agro-waste. The Total Aerobic Heterotrophic Bacterial Counts increased from 8x105 cfu/g to 8.7 x 107 cfu/g, Hydrocarbon Utilizing Bacterial Counts increased from 2x105 cfu/g to 5.9 x 107 cfu/g, whereas the Total Aerobic Heterotrophic Fungal Counts increased from 2x105 cfu/g to 8.4 x 106 cfu/g, Hydrocarbon Utilizing Fungal Count increased from 3.0x104 cfu/g to 5.4 x 106 cfu/g. The percentage biodegradation of crude oil after the treatment of the contaminated soil with the agro-wastes increased from 2.57 % to 89.05 % after 56 days. Gas Chromatographic and Mass Spectrophotometric analysis of the residual oil revealed that there was reduction in the Total Petroleum Hydrocarbon (TPH) as a result of the rapid degradation by microorganisms. There were significant differences (P<0.05) when both agro-wastes (horse dung and unripe plantain peels) were added to the crude oil contaminated soil when compared to the agro-waste when added individually. Both agro-wastes (Horse dung and Unripe plantain peels) are good biostimulants for remediation process however the treatment with the higher quantity of the combined agro-wastes (20 % horse dung (HD) and 20% unripe plantain peel (UPP)) caused the highest increase in the microbial growth, percentage biodegradation and with the least total petroleum hydrocarbons remaining at the end of the remediation process.