Xiaohui Cheng

Influences of calcium sources on microbially induced carbonate precipitation in porous media

Abstract The technology of microbially induced carbonate precipitation (MICP) provides a promising approach of improving the durability and the safety of concrete structures. CaCl2, the common calcium source of MICP, may be detrimental for the steel bars and significantly affects the durability of the reinforced concrete. Therefore, alternative calcium sources and their feasibility are investigated in the paper. The uniaxial compressive strength tests and the water absorption ratio tests are carried out for the biogrouted sand columns treated with different calcium sources, and the mineralogical compositions, the microstructure morphology and the pore size distribution of the MICP of the samples are analysed in detail. Results show that the samples using Ca(CH3COO)2 as the calcium source possess a higher strength and a wider distribution of pore size than those using CaCl2 or Ca(NO3)2. The crystal type of the MICP of the samples treated with Ca(CH3COO)2 is mainly aragonite, while that of the others is mainly calcite. It is believed that Ca(CH3COO)2 is a suitable alternative calcium source to replace CaCl2 for the MICP technology applied in the reinforced concrete structures.

Application of Response Surface Methodology for Carbonate Precipitation Production Induced by a Mutant Strain of Sporosarcina pasteurii

The application of microbial technology has brought new opportunities for the development of civil engineering. Microbial induced carbonate precipitation (MICP), which use microbial catalyzed hydrolysis of urea to produce calcium carbonate crystals chemically and physically similar to sandstone, could increase strength and stiffness of sands or stones. In this work we investigated the process of calcium carbonate precipitation induced by Sporosarcina pasteurii . To improve the yield of calcium carbonate precipitation, the strain of S. pasteurii was isolated and screened after NTG (N-methyl-N-nitroso-N-nitrosoguanidine) mutated. Mutant strain B-20 gave the highest MICP production. The urease activity was tested on different medium with byproducts; soyabean meal was the selected major components of medium. Then, the optimization of culture medium for enhanced urease activity was conducted employing response surface methodology. Plackett-Burman design was firstly used to screen the most important variables, and subsequently central composite design was adopted to investigate the optimum value of the selected factors for achieving maximum urease activity and MICP yield.

Biomineralization of Carbonate by Terrabacter Tumescens for Heavy Metal Removal and Biogrouting Applications

AbstractThe ability of Terrabacter tumescens to precipitate carbonate minerals has been demonstrated for the first time. Biomineralization of nickel, copper, lead, cobalt, zinc, cadmium and calcium by T. tumescens and mineral precipitations in both liquid and porous media were investigated. T. tumescens produced the enzyme urease which can hydrolyze urea. Due to this enzymatic reaction, soil pH increased and carbonate was produced, which results in mineralization of the soluble heavy metal ions present in soil water and their ultimate conversion to carbonates. And we studied the process of calcium carbonate precipitation induced by T. tumescens in sand column. The precipitated minerals were studied by scanning electron microscopy and X-ray diffraction, bioaccumulated divalent metal cation were deposited around the cell envelope as rhombohedral, sphere and needle shaped crystalline carbonate compounds. T. tumescens can play important role in heavy metal bioremediation and increase the strength and stiffnes...

Closed Solutions for Transient Heat Transport in Geological Media: New Development, Comparisons, and Validations

The analytical solution for temperature distribution in an aquifer was derived from Lauwerier’s plane-symmetric model (J. Appl. Sc. Res., A5(2–3):145–150, 1955). A deficiency of this solution is that it does not consider the effect of heat conduction in the aquifer. Six years later, an analytical solution that considered the effect of heat conduction under adiabatic conditions was presented by Ogata and Banks (US Geol. Survey, 1961). Closed form solutions for the plane-symmetric model of heat transport during steady-state flow that considered both heat conduction and heat convection were provided by Barends (SPE Annual Technical Conference and Exhibition, Florence, 2010). The distinctions between these solutions are discussed in this paper. Barends’ solution is more complete than those offered in previous studies. But it could be readily used for engineering applications as long as users can evaluate numerically or analytically the integrals involved in this solution. This paper introduces a plane-symmetric model under Cauchy’s boundary condition that considers heat conduction and convection. The Laplace transform technique is applied to obtain the solution for this model, and two important parameters (the Peclet number and the convective heat transfer coefficient) are discussed in detail. The result of this simplified solution agrees well with that of the numerical solutions (Ansys and Comsol).