Entrapment of clay particles enhances durability of bacterial biofilm-associated bioclogging in sand

Abstract

Utilization of bacterial biofilms and extracellular polymeric substances (EPS) for engineered bioclogging has recently garnered increasing attention in various geotechnical practices, such as leakage sealing in water-front structures, soil erosion protection, earthquake-induced liquefaction mitigation, and hydraulic barrier installation. However, the long-term durability is still questioned as to how long the biofilm-associated bioclogging would last as the biofilms readily degrade in nutrient-poor conditions. Therefore, we explore the feasibility of using fine clay particles to enhance the durability of biofilm-induced bioclogging. A series of column experiments were performed to compare the clogging durability of bentonite-associated biofilms against that of biofilms only. The results confirmed that a continuous feed of nutrients to the model bacteria, Bacillus subtilis, stimulated biofilm formation and caused a similar to 99% reduction in hydraulic conductivity of sands. However, nutrient-poor fluid flow caused instantaneous sloughing of biofilms and removal of bioclogging. By contrast, bioclogging associated with bentonite-biofilm aggregates demonstrated enhanced durability against shear detachment by fluid flows in a starved condition. EPS analysis and SEM imaging revealed that bentonite particles in the introduced suspension formed aggregates with biofilms by coating and being embedded within biofilms. This study suggests that the exploitation of bentonite-biofilm aggregations can remarkably enhance bioclogging durability in nutrient-poor conditions. This coupled clay-biofilm clogging approach is expected to provide benefits in developing a strategy for engineered bioclogging in geotechnical practices.