Suitability of Various Ureolytic Microbes for Potential Soil Strengthening via Biocementation

Biocementation or microbially induced calcium carbonate precipitation (MICP) is a feasible biochemical process in enhancing the behavior of geomaterial, that is, soil strengthening and/or remediation. This biochemical process encounters several biotic and abiotic challenges while implementing it in real field conditions. With this, the present study aims to investigate the efficiency and suitability of different ex situ and in situ ureolytic microbes in enhancing the geotechnical properties of the sand in different environmental conditions. The studies of MICP revealed a hindrance of microbial growth and ureolytic enzyme activity of one ex situ strain of S. pasteurii in the prevailing soil anoxic (air restrict) or anaerobic condition. The hindrance was the major reason for the minimal amount of precipitation and no strength gain in the biomodified sample. In contrast, high compressive strength was achieved with an abundant amount of precipitation for the sample catalyzed by another strain of S. pasteurii and isolated Proteus species. The results showed that the specific urease activity varies substantially pertaining to the type of microbes in similar chemical and environmental conditions which directly impact the biomineral precipitation and the rate of strength enhancement. The whole study recommends two major tools, that is, the value of specific urease activity and the ureolysis rate in the prevailing soil condition to compute the suitability of the ureolytic microbe for a successful MICP implementation.