Bioclogging

Bioclogging or biological clogging is the clogging of pore space in soil by microbial biomass; their body and their byproducts such as extracellular polymeric substance (EPS). The microbial biomass blocks the pathway of water in the pore space, forming a certain thickness of the impermeable layer in the soil, and it reduces the rate of infiltration of water remarkably. Bioclogging is observed under continuous ponded infiltration at various field conditions such as artificial recharge ponds, percolation trenches, irrigation channels, sewage treatment systems, constructed wetlands, and landfill liners. It also affects groundwater flow in the aquifer, such as ground source heat pumps, permeable reactive barriers, and microbial enhanced oil recovery. In the situation where infiltration of water at an appropriate rate is needed, bioclogging can be problematic and countermeasures such as regular drying of the system are taken. In some cases, bioclogging can be utilized to make an impermeable layer to minimize the rate of infiltration. Bioclogging is observed as the decrease in the infiltration rate. A decrease in the infiltration rate under ponded infiltration was observed in the 1940s for studying the infiltration of artificial recharge ponds and the water-spreading on agricultural soils. When soils are continuously submerged, permeability or saturated hydraulic conductivity changes in 3 stages which was explained as follows. Permeability decreases for 10 to 20 days possibly due to physical changes in the structure of the soil. Permeability increases due to dissolving the entrapped air in soil into the percolating water. Permeability decreases for 2 to 4 weeks due to the disintegration of aggregates and biological clogging of soil pores with microbial cells and their synthesized products, slimes, or polysaccharides. The 3 stages are not necessarily distinct in every field condition of bioclogging; when the second stage is not clear, permeability just continues to decrease. The change in permeability with time is observed in various field situations.