Modelling bioaugmentation in unsaturated porous media: The linuron herbicide example

To protect groundwater resources against pesticides, bioaugmentation with microorganisms immobilized in solid carriers has been considered as a soil remediation strategy. We have developed a mathematical model to assess this bioremediation approach to remove the pesticide linuron from soils at various water saturation levels. A bacterium mineralizing linuron is heterogeneously distributed within a 3-D model domain in spherical hotspots of 2-mm diameter size. Diffusion and advection due to infiltration are the transport processes, and microbial growth follows first order kinetics. Without advection, a bead spacing distance of 5 mm at saturated conditions is required to achieve a bioremediation goal of 90% linuron mineralization in 1 year. The gas phase is an important parameter affecting the transport of linuron, however, linuron biodegradation is growth kinetics limited within a broad water saturation range. It is hypothesized that the selection of faster degraders can compensate for high amounts of required beads.