Design of an Impermeable Layer for the Landfill Final Cover with Biogrouting Method

Abstract

Leachate accumulation is mainly caused by water seeping through the top of the landfill, whether from direct precipitation or inflow runoff. Surface water infiltration, such as from precipitation, is prevented by an impermeable layer. Utilization of dredged material from the Bili-Bili Dam in Gowa, South Sulawesi, and the pure culture bacteria of Bacillus subtilis subsp. spizizenii derived from ATCC 6633 to improve soil engineering properties. This study aims to find out how the pure culture of the bacterium Bacillus subtilis subsp. spizizenii ATCC 6633 improves the engineering properties of sedimentary soil as an impermeable layer for the landfill's final cover through physical, mechanical, and chemical characteristics tests in the laboratory. Pure cultures were inoculated with an incubation period of 24 hours at 37 °C (Celsius). While the nutrients used by Bacillus subtilis subsp. spizizenii bacteria are urea (NH₂)₂CO and calcium chloride (CaCl₂). According to the AASHTO and USCS classifications, sedimentary soils include low plasticity (ML) silts and poor to poor subgrades. The molarity of the solution used was 0.8 M (mol/L). The maximum dry density (MDD) and the optimum moisture content (OMC) were achieved when the bacterial variation was 12%. A bacterial variation of 12% reduced soil permeability, soil crack intensity factor, and volume shrinkage of soil. Based on a chemical approach, a bacterial variation of 8% showed an alumina increase. In comparison, mineralogy found aragonite carbonate crystal minerals (CaCO₃) at 8.8%, increasing soil's unconfined compressive strength, cohesion, and friction angle. The decrease in soil strength when 10% and 12% bacteria were added was justified due to the destruction of the carbonate crystal mechanism on the soil specimen.