Biofilm Characterization and Establishing Microbial-Induced Calcite Precipitation Treatment Process for Ganga River Sand by Using the Sand Column Method

Abstract

Biocementation using the microbial-induced calcite precipitation (MICP) technique is an environmentally friendly method that imitates the natural cementation phenomenon to improve the behavior of soils. Urea hydrolysis performed by ureolytic microorganisms results in the immobilization of the calcium ions by electrostatic attraction, leading to the formation of calcite crystals. The Ganga River sand (GRS) used in the present study is a fine-grained sand possessing serious engineering problems and in need of such improvements, for which a detailed study is necessary beforehand. Hence, the present study has explored the competence of different soil bacterium of the Bacillus family i.e., Bacillus sphaericus, Bacillus sp., and Bacillus subtilis in hydrolyzing urea, and also for forming the desirable biofilm over GRS in India. The colloidal behavior of the prepared bacterial solution along with the hydrodynamic diameter for different bacteria and its importance in the biofilm formation over GRS particles have been examined. The study is extended to determine biofilm formation’s competence for urea hydrolysis and calcite precipitation at different intervals. It is revealed that the biofilm formed by B. subtilis was stronger but the precipitation by B. sphaericus was maximum with 23% precipitation. Further, the rate of precipitation over time and its effect on the morphology of calcite crystals for all the selected bacteria have been discussed. MICP is a natural method of soil improvement. The microorganisms used for this treatment are nonpathogenic which precipitates calcite in the sand pores and over the surface of sand particles. This phenomenon leads to the densification of the sand by calcite precipitation in the pores which is responsible for the enhanced geotechnical properties. By controlling the rate of precipitation, MICP can be useful in different applications like strengthening sand, bioremediation of toxic metals, surface erosion control, liquefaction resistance, permeability reduction, soil stabilization, seal fractures, carbon sequestration, and so forth. The treatment requires the least amount of energy input and only the specific metabolism pathway of bacteria is needed for this method. The technique is comparatively easier to apply in the fields and requires little to no additional skills for implementation. MICP also finds its usage in concrete technology alongside ground improvement techniques. This technique is useful for the production of self-healing concrete, bio-bricks, and so forth. Its application goes far beyond the boundaries of civil engineering projects and requires an interdisciplinary approach to understand its full potential.