Abstract:
Oil exploitation in the Niger Delta has resulted in widespread hydrocarbon pollution. Despite vast research on bioremediation using organic amendments for restoring hydrocarbon contaminated land, the potential of decomposed cassava peels has attracted little attention in the literature. This study was therefore designed to examine the seasonal effect of decomposed cassava peels for bioremediation of hydrocarbon polluted soils of different topographical surfaces in Obio/Akpor Local Government Area(LGA), Rivers State, Nigeria.
Ecosystem concept was adopted while experimental research design was used. A well-drained and waterlogged sites were purposively selected for the study. Each site was divided into 18 plots, each measuring 2m by 2m and was contaminated with Bonny light crude oil at three levels of 2.0, 4.0 and 6.0% concentrations. The experiment was undertaken in both dry and wet seasons. The baseline soil without contamination served as control. Decomposed cassava peels were introduced into the soil to a depth of 10cm seven days after contamination. Seventy two soil samples were collected from 0-15cm and 15-30cm depth. Soils in the experimental sites were analysed before and after contamination, and after three months of bioremediation for physical (sand, silt and clay, bulk density, total porosity) and chemical (Total Organic Carbon-TOC, Total Nitrogen-TN, Phosphorus-P, pH, Total Hydrocarbon Content-THC, and Total Petroleum Hydrocarbon-TPH) properties respectively. The properties of polluted soils before and after remediation were compared using descriptive statistics and independent t-test at p<0.05.
The TOC, TN, P and pH of soils before and after contamination, and after remediation were: 0.37%, 0.08%, 0.67mg/kg and 6.39; 0.72%, 0.21%, 0.82mg/kg and 6.4; and 0.58%, 0.16%, 0.51mg/kg and 6.22, respectively. These indicated an increase in the parameters after contamination and decrease after remediation. Percentage reduction in TPH was 58.2% in dry season and 24.8% in wet season. The THC in dry seasonbefore contamination were 40.63mg/kg, 32.5mg/kg and 36.67mg/kg in well drained site and 35mg/kg, 30mg/kg and 40mg/kg in waterlogged site for 2.0, 4.0 and 6.0% levels of contamination. After contamination, THC increased to 740.8mg/kg, 755mg/kg and 787mg/kg in well drained site and 882.5mg/kg, 912.5mg/kg and 935mg/kg in waterlogged site. After remediation THC decreased to 339.2mg/kg, 317.5mg/kg and 436.7mg/kg in well drained site and 525.1mg/kg, 462.6mg/kg and 558.2mg/kg respectively in waterlogged site. In the wet season THC results before and after contamination, and after remediation were 85.8mg/kg, 100.8mg/kg and 121.7mg/kg; 470mg/kg, 598.3mg/kg and 827mg/kg; and 238.2mg/kg, 350mg/kg and 486.7mg/kg respectively. The THC was significantly lower in remediated soils t(5)=15.12. The TPH reduced from 69.7ppm to 29.1ppm in dry season, while in wet season TPH declined from 58.9ppm to 44.3ppm.
Bioremediation was influenced by seasons and topographical locations in Obio/Akpor Local Government Area, Rivers State. Remediation was more effective in well-drained soil than in waterlogged soil but proceeded faster in the dry season than in the wetseason. Application of decomposed cassava peels for hydrocarbon remediation on well-drained soil in dry season is recommended.
