Influence of size and concentration of carbonate biomineral on biocementation and bioclogging for mitigating soil degradation

Microbially induced carbonate precipitation (MICP) is a promising technique to enhance the geotechnical properties of geomaterial either by strengthening via biocementation or reducing the hydraulic conductivity via bioclogging. This rate of modification mainly depends on the amount, and nature of biomineral precipitated and it is influenced by various environmental, chemical, and microbial factors. Given this, the present study aims to investigate the effect of biochemical conditions such as concentration of biomass and chemical reagents on the amount and nature of biomineral and its impact on the strength and permeability of biomodified sand. For this, the two microbes i.e., Sporosarcina pasteurii and isolated Proteus species at three different initial concentrations and chemical reagents by varying 0.1–1 molar of urea and calcium were considered. The amount and microstructural behavior of biomineral in different biochemical conditions concluded that the governing mechanism differs for both biocementation and bioclogging under identical MICP treatment. The strength enhancement or biocementation is dependent on the size of the biomineral precipitated whereas the reduction in permeability or bioclogging is mainly dominated by the amount of biomineral. The optimum value of biochemical conditions i.e., 10⁸ cells/ml of biomass and 0.25 M concentration of cementation reagents was chosen to further evaluate the effect of equal MICP treatment on the biocementation and bioclogging of sands having different grain sizes. The study infers that not the absolute size of the biomineral but the relative size of soil grain and biomineral influence the linkage between the soil particles and hence affect the strength of biomodified soil.