polymorphs

Microbially induced carbonate precipitation (MICP) is a biologically induced mineralization process and has found its application in various engineering realms. The process of MICP is often mediated by the enzymes urease and carbonic anhydrase. The bacterial cell wall acts as the nucleation site for the formation of CaCO3. This review summarizes the mechanism associated with the microbial CaCO3 precipitation process and the function of urease. The role of extracellular polymeric substances (EPS) and their ability to influence MICP are also discussed. The various polymorphs of CaCO3 that are formed in the due course of MICP and the conditions that determine the polymorph selection are discussed as well. Biocalcification by different classes of bacteria isolated from various sources are summarized. This review describes in detail the various applications of MICP including its role in biocementation, removal of heavy metals, CO2 sequestration, fracture sealing in underground geology, remediation of limestone structures and as a counter measure for erosion. Over the last few years, various process improvements have emerged for improving the quality of MICP and thereby enhancing their potential, viz. optimization of bacterial growth medium, using industrial by-products as growth media components, etc. Some of these process improvements are also discussed in this review. The shortfalls of MICP, particularly those while implementing it at the field level, issues associated with commercialization of the process are also described along with its future perspectives.