Bioclogging

Bioclogging or biological clogging is 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 impermeable layer in 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 trench, irrigation channel, sewage treatment system and landfill liner. It also affects groundwater flow in aquifer, such as permeable reactive barrier and microbial enhanced oil recovery. In the situation where infiltration of water at 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 impermeable layer to minimize the rate of infiltration.

Bioclogging is observed as the decrease of the infiltration rate. Decrease in the infiltration rate under ponded infiltration was observed in 1940s for studying the infiltration of artificial recharge pond 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.

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. Depending on the field condition, there are various causes for the change in the hydraulic conductivity, summarized as follows.

Bioclogging is observed under continuous ponded infiltration in such places as artificial recharge ponds and percolation trench. Reduction of infiltration rate due to bioclogging at the infiltrating surface reduces the efficiency of such systems. To minimize the bioclogging effects, pretreatment of the water to reduce suspended solids, nutrients, and organic carbon might be necessary. Regular drying of the system and physical removal of the clogging layer can also be effective countermeasures. Even operated cautiously in this way, bioclogging is still likely to occur because of microbiological growth at the infiltrating surface.

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