Treatment of Lateritic Soil Using Soya Beans Waste Ash for Landfill Liner and Cover

Abstract

This study evaluated the suitability of lateritic soil treated with Soya Beans Waste Ash (SBWA) as a liner material for municipal solid waste containment systems. SBWA was added at 0%, 4%, 8%, 12%, and 16% by dry weight of soil and compacted using British Standard Light (BSL), West African Standard (WAS), and British Standard Heavy (BSH) compactive efforts at varying moulding water contents. Leachate characterization revealed highly contaminated effluents with pH values ranging from 3.57 to 6.32, Total Dissolved Solids between 1,856 mg/l and 3,328 mg/l, lead concentrations of 0.03–0.640 mg/l, and iron concentrations as high as 46.075 mg/l, all exceeding permissible limits. Chemical Oxygen Demand ranged from 171 to 190 mg/l, indicating significant pollution strength. Geotechnical results showed that percentage fines reduced from 3.15% (natural soil) to 1.01% at 16% SBWA, indicating flocculation and agglomeration. Specific gravity decreased from 2.61 to 2.56 with increasing SBWA. Liquid limit increased from 44.50% to a peak of 48.15% at 4% SBWA, while plastic limit decreased from 25.00% to 23.24% at 8% SBWA. The plasticity index increased from 19.5% to 24.33% at 4% SBWA. Maximum Dry Density (MDD) decreased slightly with increasing SBWA, with values ranging from 1.60 Mg/m³ (natural soil, BSL) to 1.73 Mg/m³ (natural soil, BSH), reducing to 1.56 Mg/m³ (BSL) and 1.67 Mg/m³ (BSH) at 16% SBWA. Optimum Moisture Content (OMC) increased from 16.6% to 17.20% (BSL) and from 14.64% to 15.19% (BSH) with increasing SBWA. Unconfined Compressive Strength (UCS) improved significantly with treatment, increasing from a minimum of 248.01 kN/m² (natural soil at +4% OMC) to a maximum of 789.67 kN/m² at 8% SBWA under BSH compaction, far exceeding the recommended minimum value of 200 kN/m² for liner applications. Volumetric Shrinkage Strain (VSS) reduced from 5.2% (untreated soil) to as low as 1.6% at 8% SBWA, satisfying the 4% maximum design criterion. Hydraulic conductivity of the natural soil increased from 1.16 × 10⁻⁹ m/s to 3.01 × 10⁻⁸ m/s after leachate permeation, whereas 8% SBWA-treated soil showed comparatively lower long-term values of 2.24 × 10⁻⁸ m/s, indicating improved resistance to leachate attack. 8% SBWA compacted at 0% to +2% OMC under BSH effort produced the highest strength (789.67 kN/m²), lowest shrinkage (1.6%), and improved hydraulic performance, making it the optimum content for landfill liner applications.