Improving pH and temperature stability of urease for ureolysis-induced calcium carbonate precipitation

Abstract

Ureolysis-induced calcium carbonate (CaCO 3) precipitation (UICP) is a promising technology that takes advantage of urea hydrolysis. During UICP, the enzyme urease hydrolyzes urea, and calcium carbonate can precipitate in the presence of calcium (Ca 2+). This process is also known as biomineralization, and urease is found in several bacterial and plant cells. Urease must be active to enable biomineralization engineering applications such as sealing leakage pathways around wells for CO 2 sequestration. However, biotechnological reactions are limited by physicochemical conditions (temperature, pH, toxic compounds, etc.), and conditions in practice can be suboptimal. Sporosarcina pasteurii and jack bean meal (JBM) ureolytic activities were investigated while simulating potential environmental stresses such as high temperature and pH conditions. Urease was extracted from bacterial cells to evaluate bacterial urease as an alternative to plantbased ureases. Ureolytic activities and thermal inactivation for both bacterial- and plant-based ureases were similar. Urease became thermally inactivated at elevated temperatures (> 50 °C), and urease activity also decreased when pH values moved away from circumneutral pH conditions, i.e., at pH values < 5 and > 9. Urease stability was improved through immobilization for temperatures up to 60 °C and pH values between 3.7 and 4.7. While suspended urease did not demonstrate any residual activity after a one-hour exposure to pH 4.1 at 60 °C, immobilized urease remained active after the exposure. The studies presented here suggest that UICP technology may be used in a broad range of applications, and urease stability can be improved. The use of bacterially derived urease could be cost-competitive. UICP technology not only has the potential to solve various engineering challenges, but it also has the potential to replace traditional cement technologies and contribute to a more sustainable future.