Experimental Investigation of Parameter Optimization on Immobilization of Cd Contaminated Stale Refuse by MICP

[Purposes] The stale refuse obtained from landfills can be further utilized, but the problem of heavy metal pollution needs to be solved urgently. Microbially Induced Carbonate Precipitation (MICP) technology has the potential to immobilize heavy metal-contaminated soil. However, because of the complex composition of contaminated stale refuse, the reasonable technological parameters of MICP technology for remediation of contaminated stale refuse are not clear. [Methods] In this study, the simple mixing method was adopted and Sporosarcina pasteurii was used to immobilize Cd contaminated stale refuse. The technological parameters such as the volume of bacteria solution and reaction solution (i.e. urea-calcium chloride solution), the concentration of bacteria solution and reaction solution, and the treatment number were adjusted to explore the effect of immobilized treatment on stale refuse under different conditions. [Findings] The results show that the exchangeable Cd in the contaminated stale refuse can be transformed into carbonate and Fe/Mn oxides by MICP remediation. Then, the reduction rate of exchangeable Cd can be effectively improved up to 91% by increasing the volume, concentration, and treatment times of bacteria and reaction solution. There is a nonlinear quantitative relationship between mineralized calcium carbonate's precipitation yield and the reduction rate of exchangeable Cd. The reduction rate of exchangeable Cd can reach 60% when the mass increase rate reaches 20%. [Conclusions] This work proves that MICP technology has a promising application in the immobilization of Cd contaminated stale refuse.