Influence of Microbially Induced Calcite Precipitation Technique on Mitigating Rainfall-Induced Surface Erosion of the Ganga River Sand

Abstract

Microbially induced calcite precipitation (MICP) is an emerging field of microbial geotechnology for surface erosion remediation. Conventionally, Sporosarcian pasteurii bacteria are used mostly for MICP treatment to enhance the soil properties. However, the potential of other urease-producing bacteria on surface erosion prevention is underexplored and, hence, needs a detailed investigation. Further, the insight into the exposure of MICP-treated surfaces to field conditions like natural rainwater and acid rain has not been explored. In the present study, different surface models of Ganga River Sand (GRS) were prepared at 70% relative density and inoculated with three different soil bacteria, i.e., Bacillus sp., Bacillus sphaericus, and Bacillus subtilis. Samples were then treated for 10 days with the cementation solution (0.7 M CaCl2 and urea). Later, these samples were subjected to microanalysis and controlled rainfall conditions. To study the effects of natural rainfall, the rainwater parameters and rainfall intensity were kept closer to the natural conditions. Further, the durability of the biotreated GRS surface was checked against simulated acidic rainfall at a surface slope angle of 45° to examine the stability of the treated surface in unfavorable conditions. Moreover, the change in biochemical properties of the rainwater after erosion was also examined alongside the erosion rate, erosion pattern, and strength of the treated GRS surface. The sand surfaces showed an enhanced rainfall-induced erosion resistance after the MICP treatment. B. sphaericus has shown better erosion resistance performance than the other two selected bacteria in terms of effectiveness and durability. A surface strength of 612 kPa was observed for the samples inoculated with B. sphaericus . It is also revealed that MICP-treated surfaces have pronounced poor durability subjected to acid rain. Despite the effectiveness demonstrated by the MICP treatment process in surface erosion resistance, an effort toward optimization and environmental considerations should be addressed before the process is upscaled. Bioremediation of ground through the MICP process is a topic of contemporary research. It includes the augmentation of biotechnology in the geotechnical engineering field for a green, sustainable, and eco-friendly approach to ground improvement. This process eliminates the conventional use of higher energy consumption processes and harmful chemicals for surface and ground improvement. Bio-cementation has been a captivating method among researchers for soil erosion control. This process relies on the calcite byproduct for its effectiveness, which is a relatively stable compound. The performance of the MICP-treated soil surface shows promising results in erosion control with this environment-friendly approach. The problem arises when the field condition becomes unfavorable for calcite crystals, making the MICP-treated surfaces vulnerable to external agents like rainfall, freeze and thaw, wetting and drying, and so on. The goal of this study is to address and propose the risks associated with the culpability of calcite deterioration upon exposure to field conditions like rainfall. Further, this study implores the research community to address the calcite stability in adverse conditions before the large-scale application of the MICP treatment process. The sustainability and longevity of MICP-treated surfaces should be a major concern before its widespread application to prevent any catastrophic event that may arise due to the propensity of cementation material.