Assessment of urease enzyme extraction for superior and economic bio-cementation of granular materials using enzyme-induced carbonate precipitation

The cost of urease enzyme production and complex extraction procedure are widely considered as a major barrier for the use of bio-cementation via enzyme-induced carbonate precipitation (EICP) in practical engineering applications. In this paper, crude urease was extracted from soybean using a series of extraction procedures, including coarse filtration, centrifuge, and micro-filtration. Together with the commercially available pure urease, extracts of crude urease after each extraction step were collected and evaluated for their efficiency in chemical conversion efficiency and strength enhancement of the EICP process. The results indicated that the impurities of coarse-filtrated urease could protect urease enzyme, promote precipitation yield, maintain enzyme activity and stability, and improve strength enhancement. The microstructure images of the coarse-filtered enzyme-treated samples showed the transformation of crystal morphology from metastable spherical shape to rhombohedral- and polyhedral shape, resulting in effective bonding between the sand grains. A preliminary estimation of the energy requirement for the urease extraction exhibited that about 0.6 kJ of energy could be saved per 1000 U activity produced using only coarse filtration without further labor and equipment intensive centrifugation, which represents a sustainable and cost-effective approach to utilize EICP technique. Graphical abstract: [Figure not available: see fulltext.].