Non-ureolytic EICP as a novel enzymatic pathway for sustainable soil stabilization

In order to address the challenges of the modern era, such as population growth and greenhouse gas emissions, sustainable soil improvement techniques have been in high demand. In a quest to find more sustainable ground improvement methods, microbially induced carbonate precipitation (MICP) and enzyme-induced carbonate precipitation (EICP) have attracted researchers worldwide. For the first time, this study investigates a non-ureolytic enzyme-induced carbonate precipitation method using formate dehydrogenase (FDH) as a sustainable approach for soil stabilization. Unlike traditional EICP and MICP methods, this technique avoids ammonium by-products, providing an environmentally friendly alternative. FDH activity was optimized at pH 7.6 and 37 °C. Its thermal stability was found to be reasonably suitable for biogeotechnical applications, maintaining over 90% efficiency up to 50 °C and achieving over 50% efficiency at 60 °C. The compressive strength of non-ureolytic EICP-treated soil samples and calcium carbonate content were investigated across various treatment cycles on poorly graded sand (SP). The optimal enzyme concentration was 75 mg/L with 50 g/L of calcium formate. Soil treated with this method exhibited a 31-fold increase in strength after five treatment cycles, with 1.89% calcium carbonate precipitation. Microstructural analyses (XRD, FTIR, SEM) and calcium carbonate content measurements using the Bernard calcimeter confirmed the formation of carbonate crystals between soil grains, contributing to this strength enhancement.