Biodegradation of artisanally refined diesel and the influence of organic wastes on oil-polluted soil remediation

Abstract

The increasing rate of oil-pollution in the Niger Delta due to artisanal crude oil refining has led to the destruction of farmlands/aquaculture and loss of biodiversity. The aim of this study was to determine the effect of poultry waste, granite dust and palm bunch ash on the rate of hydrocarbon degradation. Oil-polluted soil was obtained from an artisanal refining site in the Niger Delta and amended with various combinations (granite dust + poultry waste + palm bunch ash (1:2:1), granite dust only, poultry waste only) of the wastes. Chemical parameters monitored for 70 days included total petroleum hydrocarbons (TPH), polycyclic aromatic hydrocarbons (PAHs), nitrate, phosphorus, potassium and the soil pH. The degradative potentials of the isolated indigenous bacterial species were determined using redox indicator 2,6-dichlorophenolindophenol (DCPIP). Bacterial classification was determined using 16S rRNA gene as molecular marker. Initial TPH (16,388.88 mg/kg) and PAHs (8,579.26 mg/kg) exceeded Department of Petroleum Resources’ intervention limits of 5000 mg/kg and 40 mg/kg for TPH and PAHs respectively. The rate of hydrocarbon removal was significantly higher in the treatment amended with the combined waste materials (0.04 d-1) than the treatments amended with a single waste (0.02 d-1). TPH in the combined waste treatment reduced from 16,000 mg/kg to 533.85 mg/kg on day 70 while pH increased from 6.1 to between 6.8 and 7.1 in all treatments following amendment with nutrients. Observed increases in hydrocarbon utilizing bacterial counts significantly correlated with pH (R = 0.82; p = 0.04), phosphate (R = 0.93; p = 0.006) and TPH (R= -0.88; p = 0.02) reduction. The degradation studies revealed that the artisanally refined diesel was less biodegradable with the genera Lysinibacillus and Providencia demonstrating the strongest biodegradation potential. This study would be relevant for designing engineered remedial strategies for the clean-up of hydrocarbon spills related to artisanal refining as the extant indigenous microbes in this region are mostly hydrocarbon degraders.