ABSTRACT
A study was conducted in the laboratory on a crude oil contaminated soil treated with Bacillus licheniformis to investigate the suitability of the material for use as a liner material in waste containment applications. An indigenous hydrocarbon utilizing bacteria (HUB) was identified as Bacillus licheniformis and isolated from crude oil contaminated soil (COCS) collected from the Nigerian National Petroleum Corporation (NNPC) Kaduna, Nigeria, at a depth of 0.5m from the surface. A bio-stimulation strategy of bio-remediation was adopted using chicken droppings (CD) in stepped concentrations of 0, 10, 20, 30 and 40% CD content as a source of nutrients only, to activate the indigenous bacteria for a 12 weeks period of remediation. At the end of the remediation, it was observed that Bacilluslicheniformis removed 89.8% of crude oil content out of the initial 98g/kg of total petroleum hydrocarbon concentration at 30% CD dosage. The bio-remediated soil was further subjected to microbial activity with a view to improve the engineering properties of the soil using the Bacillus licheniformis suspension in stepped concentrations of 0, 1.5x108, 6.0x108, 1.2 x109, 1.8 x109 and 2.4 x109 cell/ml suspension densities of one-third of the pore volume ( 1/3), mixed with soil for 12hours and two-third (2/3) of the pore volume of the cementation reagent injected by gravity flow in four cycles. Preparation of samples were done at optimum moisture content (OMC) using three compactive efforts namely; British Standard light (BSL), West African Standard (WAS) and British Standard heavy (BSH) and the following tests were carried out: Index properties, compaction characteristics, unconfined compressive strength (UCS), volumetric shrinkage strain (VSS) and hydraulic conductivity. The results showed that there was increase in liquid and plastic limits with increase in Bacillus licheniformis dosage. The plasticity index decreased with increase in the microbial flora. The hydraulic conductivity value reduced to 9.92 x 10-11m/s for samples treated with 2.4 x109 cell/ml of Bacillus licheniformis suspension and compacted using BSH compactive effort. Void ratios consistently decreased with higher doses of microbial flora in the bio-remediated and bio-cemented crude oil contaminated soils. Minimum void ratio values obtained at 2.4 x 109cell/ml of B. licheniformis of 0.83, 0.74 and 0.62 respectively, when compacted using BSL WAS and BSH compaction energies. There was reduction in porosity with increasing microbial content. Similarly, samples containing higher doses of the microbial flora attained higher degree of saturation for all the compactive efforts considered. The UCS values of the crude oil contaminated soil were 119.56, 202.82 and 253.15 kN/m2 while for samples treated with 1.5 x108cell/ml of B. licheniformis suspension, the UCS values were 330.64, 415.57 and 460.78kN/ m2, when compacted using BSL, WAS and BSH compactive efforts, respectively. For VSS, only higher doses of the bacterial specie of up to 2.4 x 109 cell/ml of B. licheniformis yielded the VSS values of 3.98, 3.78 and 3.06 % respectively which satisfied the maximum permissible value of 4%.
