Hydraulic conductivity change of bio-barrier formed in the subsurface by the adverse conditions including freeze–thaw cycles

Bio-barrier is an emerging technology to control subsurface contaminant plum by making microorganisms clog soil pore to form a subsurface barrier. Extracellular polymeric substances (EPS) of microorganisms play an important role to maintain decreased hydraulic conductivity. In this research, the hydraulic conductivity changes of biomass–soil mixtures by the adverse conditions were studied to evaluate the applicability to the field condition as an alternative barrier material. The microorganisms used in this research were bacterium, Azotobacter chroococcum, and fungus, Aureobasidium pullulans, respectively. The hydraulic conductivity decreased to 1–10% of the initial hydraulic conductivity of residual soil, 1×10−4 cm/s, and stayed constant while substrate was provided. Under adverse conditions such as no substrate available, chemical solution permeation and freeze–thaw cycles, the hydraulic conductivity increased by 30–50% compared to the lowest value. The decrease of hydraulic conductivity in a fungus–soil mixture was faster than that of a bacterium–soil mixture. The fungus–soil mixture, however, was more sensitive to the adverse conditions. After the adverse conditions, hydraulic conductivity shows even lower value compare to that of before the adverse conditions.