Use Of Biochar To Enhance Bioremediation Of An Oxisol Contaminated With Diesel Oil

ABSTRACT Oil pollution is a worldwide threat to the environment, especially in oil producing countries, and the remediation of oil-contaminated soils is a major challenge for environmental research. Bioremediation is a useful method for restoring oil contaminated soils because of its cost effectiveness and environmental friendliness. However, the process is very slow in soils with low pH. Soils of the Western Region of Ghana where most of the country‘s oil activities take place are classified as Oxisols. These soils are acidic in nature and have soil conditions unfavourable for effective biodegradation of petroleum and its products. Application of biochar to soils is currently gaining considerable interest globally due to its potential to serve as a liming agent and in raising soil pH in different soil types. It is against this background that the present study was carried out to investigate the effectiveness of biochar as a soil conditioner in enhancing microbial degradation of diesel oil in theAnkasa series (Plinthic acrudox) sampled from the Western Region of Ghana and the subsequent growth of cowpea in the bioremediated soils. The acidic soil was contaminated with diesel oil at 100 mL/kg soil. Two biochar types, from rice straw (RB) and from saw dust (SB), were applied to the contaminated soils at 0, 65, 130, 195 and 260 Mg/ha. The treated soils were incubated and sampled for determination of the hydrocarbon utilizing bacteria (HUB) population, total aerobic heterotrophic bacteria (HET) population, change in soil pH and the amount of oil degraded at 10 days interval for 40 days. In another experiment the soil was contaminated with diesel oil at 100 mL/kg soil, amended with RB at 195 Mg/ha and fertilized with N and/or P in the form of ammonium nitrate and single super phosphate, respectively at 60 kg/ha. These treated soils were also incubated and sampled for analysis of hydrocarbon utilizing bacteria (HUB) population and the amount of oil degraded at 10 days interval. Cowpea was sown into the residual soils and harvested 6 weeks after planting for the determination of the number of nodule formed, shoot and root dry weights. In the first v experiment, results showed that all the biochar treatments significantly (p < 0.05) increased the amount of diesel oil degraded, HUB and HET populations when compared to the control.The RB treatments significantly (p < 0.05) enhanced diesel oil degradation more than the SB treatments. Results also showed that RB at 260 Mg/ha resulted in the highest amount of diesel oil degraded but was not significantly (p > 0.05) different from RB at 195 Mg/ha. Soil pH, soil organic carbon, total exchangeable bases, effective cation exchange capacity, and base saturation were also significantly (p < 0.05) increased by the biochar treatments. Soil available P increased significantly (p < 0.05) for the RB treatments. However, total N and exchangeable acidity significantly (p < 0.05) decreased when amended with biochar. X-ray diffraction analysis showed that these biochars contained large quantities of carbonates and oxides.Fertilizing RB (195 Mg/ha) with N and/or P significantly (p < 0.05) increased amount of diesel oil degraded and HUB population 40 days after incubation when compared to RB only treatment. Fertilization with N and/or P enhanced shoots and roots dry weights of cowpea. Addition of N was inhibitory to nodulation, however, P fertilization enhanced nodulation. In conclusion, the enhanced degradation was attributed to the presence of large quantities of carbonates and oxides in the biochars which might have served as liming agents, improved the soilmicrobiology and other chemical properties. Further studies should be conducted on the application of combination of rice straw biochar, nitrogen and phosphorus, in the bioremediation of oil under acidic condition should be conducted in the field to confirm its effectiveness for future recommendation.