Compatibility interaction of landfill leachate with lateritic soil bio-treated with Bacillus megaterium: Criterion for barrier material in municipal solid waste containment

Abstract

This study assesses the compatibility performance of microbial induced calcite precipitate bound lateritic soil using Bacillus megaterium (B. megaterium) for hydraulic barrier of sanitary landfill. Compacted treated lateritic soil specimens were permeated with water only, sequentially with water and leachate as well as with leachate only for 90 days, respectively, to evaluate its long-term performance in line with conventional hydraulic conductivity (k) criterion ≤ 1 × 10-9 m/s for municipal solid waste (MSW) barrier application. The compacted specimens were prepared by mixing 1/3 pore volume (PV) of stepped B. megaterium suspension density of 0, 1.5 × 108, 6 × 108, 1.2 × 109, 1.8 × 109, and 2.4 × 109 cells/ml relative to the predetermined optimum moulding water content (OMWC) by dry weight of dry soil. 2/3 PV cementation solution was used to flood the specimens in 3 cycles and allowed to percolate by gravity for 6, 12 and 24 h for each cycle, respectively. The results show that the hydraulic conductivity (i.e., coefficient of permeability k) decreased with time for most part of the test for all cases of permeation in the order water only ˃ water and leachate ˃ leachate only. The compatibility increased with leachate interaction as a result of biofilm formation, which for most part satisfied the k criterion except for few instances where the k values were marginally greater. The morphological changes due to physicochemical transformation obtained from scanning electron microscopy (SEM) /Energy Dispersive Spectroscopy (EDS) and Fourier transformation infra-red (FTIR) spectroscopy microanalysis established the presence of calcite. The calcite content that showed a non-uniform distribution of calcite with depth of permeation was due to increased biofilm accumulation that clogged the soil pores. The results also showed that compatibility is not dependent on the physicochemical interactions and precipitation of calcite only, but also on biofilm formation.