Biomineralization of coral sand by Bacillus thuringiensis isolated from a travertine cave

Travertine is a typical product of microbial mineralization in the nature and its mineral composition is mainly calcite and aragonite. In this paper, Bacillus thuringiensis, a kind of mineralize bacterium is extracted from the travertine crystal to cenment coral sand, and the reinforcement effect of microbial induced carbonate precipitation (MICP) technology on coral sand under different cementation times is studied. Firstly, the culture conditions are optimized in nine pairs of trials, including urea content, microbial inoculation, shaker speed and incubation time. Under the optimal culture conditions, the coral sand is cemented by soaking method. With the increase of reinforcement times, the permeability coefficient of the sand sample is reduced to 10^-4 cm/s, and the shear strength is increased by more than 130%. Compared with Sporosarcina pasteurii, the cohesion and internal friction angle of the coral sand column cemented by Bacillus thuringiensis are increased by more than 50% and 10%, respectively. The area distribution of T₂ spectrum shows that with the increase of the number of cementation, the amplitude of the main peak decreases, indicating that the large pores are better filled, the number of medium and small pores are also reduced, and the pore area is significantly reduced, with the amplitude of about 44%. The above experiments verified that microorganism in travertine could also be used in MICP technology, and even achieve better reinforcement effect. It also provides a new way and idea for the selection of mineralized bacteria by MICP technology.