Biotreatment of incinerated bottom ash and biocementation of sand blocks using soybean urease

Because of the high cost of cultivating urease-producing bacteria (UPB), this paper proposes soybean-urease-induced carbonate precipitation (SUICP) as a novel biocement for treatment of nickel contaminants and cementation of sandy soil. We found the optimal soaking time and soybean-powder content to be 30 min and 130 g/L, respectively, based on a standard of 5 U of urease activity. The most efficient removal of nickel ions is obtained with an ideal mass ratio of urea to nickel ions to soybean-powder filtrate (SPF) of 1:2.4:20. The removal efficiency of nickel ions can reach 89.42% when treating 1 L of nickel-ion solution (1200 mg/L with the optimal mass ratio). In incinerated bottom ash (IBA), the removal efficiency of nickel ions is 99.33% with the optimal mass ratio. In biocemented sandy soil, the average unconfined compressive strength (UCS) of sand blocks cemented with soybean urease-based biocement can reach 118.89 kPa when the cementation level is 3. Currently, the average content of CaCO₃ in sand blocks is 2.52%. As a result, the SUICP process can be applied to remove heavy metal ions in wastewater or solid waste and improve the mechanical properties of soft soil foundations.