Evaluation of Strength Properties of Bio-remediated Crude Oil Contaminated Soil using Bacillus pumilus for Use as Liner and Cover Material in Municipal Solid Waste Containment Applications

This study evaluates the effectiveness of Bacillus pumilus -induced calcite precipitate to enhance the engineering performance of bio-remediated crude oil-contaminated soils for waste containment applications. Remediated soil samples were bio-treated with Bacillus pumilus (B) – cementation reagent (C) mixtures. Trial mix ratios of 75% B – 25% C, 50% B – 50% C, and 25% B – 75% C with B. pumilus suspension densities in the range 1.5 × 10⁸ − 2.4 × 10⁹ cells/ml and a fixed cementation reagent concentration. The 50% B – 50% C ratio yielded optimum improvement and was adopted in this study. The cementation reagent was prepared and applied to soil samples compacted using three energy levels namely, British Standard light (BSL), West African Standard (WAS), and British Standard heavy (BSH). The bio-cementation with B. pumilus (1.5 × 10⁸ to 2.4 × 10⁹ cells/ml) cementation solutions under gravity infiltration on the post-remediated soil specimens showed slight improvements with liquid limit reducing from 43.8% to 41.1%, plastic limit increased from 36.3% to 37.5%, and the plasticity index increased from 7.3% to 7.4%. UCS values reached 225.4, 264.4, and 385.1 kN/m² for BSL, WAS, and BSH compaction, respectively, recorded exceeded the minimum requirement of 200 kN/m². The findings confirm that bio-cementation using B. pumilus can effectively enhance the strength and plasticity characteristics of bioremediated oil-contaminated soils, supporting their suitability as liner and cover materials in waste containment systems.