Biochar-assisted bio-cementation of a sand using native bacteria

Abstract

Microbially induced calcite precipitation (MICP) is a ground improvement method often driven by ureolytic bacteria to precipitate calcite in a soil mass. While in previous studies MICP was often accomplished by the injection of exogenous bacterial solutions, this study utilizes the soil’s native ureolytic microorganisms. The roles of yeast extract, molasses, and biochar as different sources of carbon and nutrients for stimulating native microorganisms are examined and compared with MICP induced by bioaugmentation. Biochar as a carbonized biomass has the potential to enhance a soil’s enzymatic activity by providing high concentrations of organic carbon, phosphorus, and ammonium nitrogen, making it an attractive substance to catalyze ureolysis and bio-cementation in the field. In this research, a mixture of wheat straw and sugarcane bagasse is used to produce biochar. This material is then enriched with sugarcane molasses and mixed with specimens of a natural sand to stimulate native microorganisms with a long-lasting source of energy and produce ureolytic enzymes for bio-cementation. After 5, 10, and 15 cycles of injecting the cementation solution, shear strength and permeability of treated specimens were measured in direct shear and hydraulic conductivity tests. The specimens’ structural changes were also examined using scanning electron microscopy (SEM) images and energy-dispersive X-ray spectroscopy (EDS). The results show a higher gain in strength and lower permeability in biochar-assisted microbially treated sand specimens compared to the untreated sand. Physical model experiments conducted in this study further demonstrated the application of this technique along with natural microorganisms for stabilizing a model slope against wave-induced erosion.