Soil stabilization using biological CO2 sequestration and CO2-based biocementation technique

As global concern about climate change has risen, the importance of climate action and reducing greenhouse gas emissions has intensified. CO 2 -based biocementation represents a sustainable approach that combines soil stabilization and CO 2 sequestration, potentially contributing to global emission-reduction goals. In this method, atmospheric or industrial CO 2 is enzymatically or microbially converted into calcium carbonate precipitates within the soil. This mineralization enhances the mechanical properties of the treated material while permanently capturing CO 2 in a stable form. Unlike traditional ureolytic EICP and MICP methods, carbonic anhydrase (CA)-facilitated biocementation eliminates harmful byproducts such as ammonium and does not require urea, making it a safer, more environmentally friendly alternative. This study provides a comparative evaluation of Bacillus pasteurii CA and bovine cell-free CA for carbonate precipitation and soil strengthening through CO 2 sequestration, offering insights into their relative efficiency under different conditions. Initially, the stability and activity of both enzyme systems were evaluated at various temperatures. Subsequently, aqueous and soil samples were prepared and placed in a CO 2 container to assess the CO 2 sequestration efficiency. The compressive strength of treated samples and calcium carbonate content were evaluated using the unconfined compressive strength test and the Bernard calcimeter test, respectively. Microfabric and mineralogical analyses were performed using optical microscopy, XRD, FTIR, EDX, and SEM. Results indicated that bacterial CA and bovine cell-free CA exhibited optimal performance at 30 °C and 37 °C, respectively. A compressive strength of 568.4 kPa with 1.82% precipitation was achieved using bacterial CA at OD 600 = 1.5, while 473.5 kPa with 1.95% precipitation was obtained using 6 mg/L bovine CA. Furthermore, a tenfold increase in stiffness was observed. Overall, this CO 2 -based biocementation technique provides a promising, environmentally responsible method for CO 2 capture and utilization through ground improvement applications.