Effect of alum content on soybean urease solution and its biocementation

Enzyme induced carbonate precipitation (EICP) technique for soil improvement using self-extracted soybean urease solution to induce calcium carbonate precipitation has various advantages such as economic, ecological and environmental considerations. However, the high turbidity of the self-extracted soybean urease solution easily leads to bioclogging during the biogrouting process, resulting in poor biocementation. In this study, an alum-containing solvent was used for the extraction of soybean urease solution to reduce its turbidity. Incorporating soybean urease extraction, solution tests, and sand column solidification with macro- and micro-scale tests were carried out to investigate the effects of alum content on turbidity and biocementation of the extracted soybean urease solution. The results indicate that the addition of an appropriate amount of alum (e.g., 3.0 g/L for 100 g/L soybean powder content) can effectively reduce the turbidity of the self-extracted soybean urease solution without affecting its urease activity. However, excessive amount of alum may lead to a reduction or even loss of urease activity. The use of a low-turbidity soybean urease solution is beneficial in improving the uniformity of its biocementation, without an apparent effect on the morphology and crystallinity of the precipitated calcium carbonate crystals.