Urease extraction from concentrated bacterial suspension and its biomineralization of soil

Bacterial enzyme induced carbonate precipitation (BEICP) is an emerging biomineralization technique for soil improvement, yet the urease extraction efficiency remains insufficient for field applications. This study proposes a bacterial concentration pretreatment involving low concentrations of calcium chloride to enhance the urease extraction efficiency. A series of tests were conducted to investigate the effects of calcium ion concentration ( C cal ) and pH on urease extraction efficiency. Then, the sand column treatment test was conducted to evaluate the performance of the proposed pretreatment on the biomineralized sand columns. The results show that a 5-fold increase in the urease extraction efficiency is achieved under optimal conditions (pH of 8.24 and C cal of 0.03 M), which is mainly attributed to a reduction in the volume of the bacterial suspension through flocculation induced by low-concentration calcium chloride. However, the enhancement of the unconfined compressive strength of BEICP-treated sand using the urease extracted from concentrated bacteria is limited, which may be attributed to the relatively low crystallinity of the precipitated calcium carbonate crystals and the slightly lower calcium carbonate content. This is possibly caused by the calcium ions and cavitation during ultrasonic extraction and thus producing relatively lower calcium conversion efficiency. It is worth mentioning that the bacterial concentration pretreatment for efficient urease extraction can offer a promising strategy for field applications of BEICP-treatment.