Engineered bioclogging in sands: comparison of microbially induced and enzyme-induced biopolymer formation

Abstract

This study presents two methods of producing an insoluble biopolymer − microbially induced biopolymer formation (MIBF) and enzyme-induced biopolymer formation (EIBF) − and explores their ability to reduce hydraulic conductivity and cause bioclogging in soil from pore to column scales. The batch experiments confirm that insoluble polysaccharidic biopolymers, dextran, are successfully produced either by the model bacteria or by the extracted cell-free enzyme. The results show that the EIBF method is more efficient in producing biopolymer and reducing hydraulic conductivity compared to the MIBF method. This study also uses microfluidic chips, which reveals the pore-filling behaviour of biopolymers produced by both methods. EIBF produces larger dextran flocs than MIBF, and hence EIBF lowers the hydraulic conductivity more than MIBF for a given pore occupancy of dextran. Column experiments demonstrate that both MIBF and EIBF can significantly lower the hydraulic conductivity of coarse sands by two orders of magnitude with only 3% biopolymer pore saturation. The presented results suggest that both methods have the potential to induce well-controlled, engineered bioclogging in coarse-grained soils, and have applications in various geotechnical practices, such as sealing leakage in water-front structures, installing hydraulic barriers and mitigating soil erosion.