Evaluation of enzyme-induced carbonate precipitation using crude soybean urease during soil percolation

Crude urease-induced mineralization is a promising biological ground improvement technology with the advantages of low-cost and sustainability. Enzyme-induced carbonate precipitation (EICP) based on crude soybean urease (CSU) in effluents at various percolating depths was investigated to evaluate the efficiency of the bio-cementation. The unconfined compressive strength (UCS) and CaCO3 precipitation distribution of the single EICP-treated soil were measured. Soil enhancement through a single EICP followed by multiple percolations of cementation solution (urea-calcium chloride) was also examined to estimate the reusability of crude soybean urease. Experimental results indicated that the reduced urease activity and high chemical concentration cause the decreased conversion efficiency of the EICP during percolation. At a percolation depth of 50 mm, the activity of 60 g/L CSU decreased by nearly 25%, and the precipitation ratio in the EICP solution (60 g/L CSU with 1.4 mol/L urea-CaCl2) decreases from 80 to 52.6%. The progressive decrease in conversion efficiency of EICP during percolation led to an inhomogeneous distribution of CaCO3 precipitation and a non-effective improvement of UCS. The reusability of crude soybean urease was demonstrated by the uniformly increasing CaCO3 content and improved UCS after multiple percolations of cementation solution at low concentrations.