ABSTRACT
This work was aimed at investigating the effect of earthworm (Eudrilus eugeniae) and organic amendments on the bioremediation of used engine oil contaminated soil, a process thought to be limited by mass transfer. The use of organic amendment alone facilitated bioremediation. The results obtained showed that the first order bioremediation kinetics was a good description of the process. The effect of surface area and frequency of mixing were also investigated and surface area was found to be an important factor in bioremediation: having a significant effect on k (Pvalue = 0.00045), the first order bioremediation constant. Thus increasing surface area improved mass transfer. The effect of mixing on k was found to be insignificant (P-value > 0.436). For the earthworm inoculated system at a used engine oil concentration of 100g used engine oil per kg of soil, the worms recorded survivals of 100, 91.67 and 66.67% in soil contaminated with used engine oil from motorcycle, truck/lorry and motorcar respectively. Investigations into the effect of earthworm inoculation on soil properties indicated that earthworms had no effect on the carbon and nitrogen contents but had significant effects on the moisture retention and aggregate size distribution of the used engine oil contaminated soil (P-value of 0.025 and 0.029 respectively). In addition, the water holding capacity and mean weight diameter of the soil were found to increase and decrease respectively with increasing earthworm concentration. The use of earthworms was also found to have no significant effect on the microbial population as both earthworms treated and untreated samples had comparable numbers of microbial count. The effect of initial used engine oil concentration on rate of vermi-assisted bioremediation gave mixed results. At high used engine oil concentrations, the presence of earthworms accelerated the biodegradation process whereas at low initial used engine oil concentration the rate of bioremediation was favored by the absence of worms. It was also discovered that the increase in earthworm concentration favors higher rates of bioremediation. The Investigation into the uptake / elimination kinetics of some heavy metals from various concentrations of used engine oil in (12.5 – 100 g/kg) showed that Zn, Cu, Ni and Cr were eliminated from the bodies of the worms whereas Ti and Mn where accumulated. Furthermore, the metal uptake and elimination kinetics showed good fit to a one-compartment model. Earthworm assisted bioremediation of petroleum hydrocarbon contaminated soil from mechanic workshop indicated that the presence of the worms accelerated the bioremediation process (petroleum hydrocarbon degradation). The rate of bioremediation was found to be a function of the initial total petroleum hydrocarbon content as well as the percentage earthworm survival. The kinetic model made up of the combined first order reaction kinetics and first order catalysts deactivation kinetics was found to be a better fit to bioremediation (with and without earthworm inoculation) than the first order bioremediation kinetics alone in the bioremediation of simulated used engine oil contaminated soil as well as contaminated soil from mechanic workshops.