Interaction of Landfill Leachate with Compacted Lateritic Soil Treated with Bacillus coagulans Using Microbial-Induced Calcite Precipitation Approach

The performance of lateritic soil treated with Bacillus coagulans (B. Coagulans) was assessed for use as hydraulic barrier material in municipal solid waste (MSW) containment use. The soil was classified as A–4(2) and SC using AASHTO (American Association of State Highway and Transportation Officials) and the Unified Soil Classification System, respectively. Index, hydraulic conductivity, calcite content, and microanalysis tests were carried out. Soil specimens were treated with B. coagulans at one-third pore volume (i.e., the numerical difference between the initial degree of saturation before soaking in water and final degree of saturation after full saturation of the soil specimens in water) in stepped suspension densities of 0, $1.5\times {10}^8$, $6.0\times {10}^8$, $1.2\times {10}^9$, $1.8\times {10}^9$, and $2.4\times {10}^9\mathrm{cells}/\mathrm{mL}$, respectively. Cementation reagent was poured on the compacted soil in the mold and allowed to percolate until partial saturation was achieved. Compacted specimens after treatment were placed in water for 24–48 h and then permeated in three sets using water only, water and leachate, and leachate only for a total duration of 90 days. Compatibility test results showed reduction in long-term hydraulic conductivity values for the different permeation regimens considered. Absolute values recorded varied from $7.10\times {10}^{-10}$, $1.04\times {10}^{-9}$, and $7.50\times {10}^{-10}$ to $1.71\times {10}^{-9}\mathrm{m}/\mathrm{s}$, $1.69\times {10}^{-9}$, and $8.28\times {10}^{-10}\mathrm{m}/\mathrm{s}$ when permeated with water only, sequentially with water and leachate, and with leachate only, respectively, at 0 and $2.4\times {10}^9\mathrm{cells}/\mathrm{mL}$, respectively. Calcite content increased for specimens permeated with water only (i.e., from 4.00% to 4.80%) and decreased for specimens sequentially permeated with water and leachate (i.e., from 6.60% to 4.00%) and leachate only (i.e., from 4.80% to 4.00%). Results of chemical compatibility and microanalysis showed that the treated soil is compatible with MSW leachate with the exception of a few cases that did not meet the minimum permisible hydraulic conducutivity value of $1.00\times {10}^{-9}\mathrm{m}/\mathrm{s}$ used for landfill purposes.