Optimizing MICP Parameters to Minimize Ammonia Emissions and Enhance Soil Shear Strength via Response Surface Methodology

Abstract

Microbially-Induced Calcite Precipitation (MICP) is an innovative soil improvement technique in geotechnical engineering that deals with microbiological activity to enhance soil properties. Studies conducted using the techniques have shown their potential in geotechnical engineering applications. However, the ammonia generated as a by-product during the MICP process limits its broader application. This study aims to optimize the MICP input parameters to minimize the ammonia generation by incorporating zeolite, using Response Surface Methodology (RSM) for the design of the experiment. Urease-positive bacteria (Lysinibacillus fusiformis) were isolated, characterized, and identified to species level using biochemical and molecular DNA tests, which were then used for the MICP treatment. A series of laboratory experiments were conducted, varying pH, zeolite content, bacterial suspension density, cementation reagent concentration, and compactive effort. These input variables were optimized to precipitate effective calcite, improve soil shear strength, and lower the ammonia production. The results demonstrated the effectiveness of using Lysinibacillus fusiformis as a urease-producing bacterium for MICP and the potential of incorporating zeolite into the process, which significantly produced effective calcite, improved soil strength, and reduced the production of excess ammonia. Thus, the optimized MICP process with zeolite presents an effective, sustainable solution for reducing ammonia, while enhancing the geotechnical properties of silt-sand soil.