Using Microbe-induced Calcite Precipitation and Enzyme-induced Carbonate Precipitation to Cement Slopes of Earth Ditches

Abstract

【Background】 Open earth ditches are a common drainage facility to keep groundwater table below a critical depth to prevent salt accumulation, but they are prone to collapse. Traditional methods to consolidate earth trench are expensive and difficult to maintain, and biotechnological technologies such as microbe-induced calcium carbonate precipitation have become a promising alternative due to their easy operation and less impact on the environments. 【Objective】 The purpose of this paper is to study the feasibility and efficacy of microbe-induced calcite precipitation (MICP) and enzyme-induced carbonate precipitation (EICP) to consolidate and stabilize earth ditches. 【Method】 We used Sporosarcina pasteurii and urease, respectively, in this paper, with each mixed with urea-calcium chloride solution at various volumetric ratios ranging from 1∶3 to 5∶3. The mixed solution was sprayed over the soil surface. The changes in soil surface morphology, calcite content and soil microstructure in each treatment were measured periodically until they stabilized to an equilibrium. 【Result】 Both sporosarcina pasteurii and urease can be used as a catalyzer to hydrolyze urea and form calcium carbonate crystals from the calcium chloride solution. For sporosarcina pasteurii, the best result was when its ratio to the calcium chloride solution was 2∶3, while for the urease solution, the result was optimal when their volumetric ratio was 5∶3, with the highest calcium yield of the former and the latter being 86.7%, 84.1%, respectively. Spraying the soil surface with either mixture several times can fill the cracks in the soil although the calcite produced by MICP was more than that generated by EICP. However, the difference between the two waned as time elapsed; the calcium carbonate crystals formed in MICP differed from that in EICP. 【Conclusion】 Both Sporosarcina pasteurii and urease can catalyze the hydrolysis of urea to form calcite, which can fill the pores to consolidate the soil. Our experimental results showed MICP is more effective than EICP.

Keywords

• sporosarcina pasteurii
• urease
• soil cementation
• calcite content
• soil microstructure