A Comprehensive optimization study of Microbially Induced Carbonate Precipitation (MICP) for soil strength enhancement: impact of biochemical and environmental factors

Microbially Induced Carbonate Precipitation (MICP) is a biocementation technique that modifies the hydraulic and mechanical properties of porous materials using bacterial solutions. This study evaluates the efficiency of various MICP protocols under different environmental conditions, utilizing two bacterial strains: S. pasteurii and S. aquimarina, to optimize soil strength. Results indicate that bacterial strain and cementation solution concentration significantly affect biochemical outcomes, while temperature is the primary environmental factor. The efficiency of S. pasteurii's chemical conversion ranged from 40% to 80%, compared to only about 20% for S. aquimarina. MICP treatment with S. pasteurii produced CaCO3 content between 5% and 7%, whereas S. aquimarina yielded 0.5% to 1.5%. An optimized cementation solution concentration of 0.5 M was critical for maximum efficiency. The ideal operational temperature is between 20 and 35C, with salinity and oxygen levels having minimal effects. Although salinity influences carbonate crystal characteristics, its impact on Unconfined Compressive Strength (UCS) of treated soil is minor. Samples from a one-phase treatment at pH 6.0 to 7.5 showed UCS strength approximately half that of a two phase treatment. These findings suggest promising applications for MICP in enhancing strength in both terrestrial and marine environments.