Extraction of high activity bacterial urease and its application to biomineralization of soil

Biomineralization based on bacterial enzyme induced carbonate precipitation (BEICP) process is a promising alternative to cement-based ground treatment technology. The bacterial urease used in BEICP process is usually ultrasonic extracted from urease-producing bacteria. To efficiently extract urease with relatively higher activity from bacterial cells, the ultrasonic extraction parameters of urease were optimized in this study. Next, a series of bacterial urease extraction tests and sand column treatment tests were conducted to investigate the effects of vibration amplitude, upper temperature limit, and cooling method on the urease extraction process and biomineralization of sand. The results show that the upper temperature limit is an important factor affecting the extraction efficiency and the activity of the extracted urease solution, and the optimum upper temperature limit is 50 °C. The results indicate that increasing vibration amplitude could improve the extraction efficiency, but it hardly affects the urease activity (UA) under the optimal temperature. Continuous cooling could effectively simplify the operation and further improve the efficiency of urease extraction. Under the same urease activity of biotreatment solution, there is no marked difference in calcium carbonate content (CCC) and unconfined compressive strength of biomineralized sand columns prepared by urease solution extracted with different vibration amplitudes and upper temperature limits. The results of this study could provide a reference for application of BEICP technology of urease extraction to large-scale soil treatment.