The Factors Influencing Calcium Carbonate Precipitation Induced By Bacillus Sp

Microbial mineralization of calcium carbonate is considered as a common phenomenon both in the nature systems and in the laboratory cultures no matter in the past and at present time. Three mechanisms have been proposed by numerous studies about biomineralization. Microbes can firstly create a better alkaline environment by means of their physiological activities for precipitation and then induce the formation of carbonate via their metabolites and nucleation sites on the cell surface. Now more and more researchers focus on the process of microbes-mediated carbonate precipitation impacted by different factors.To study the impacts of different SO42-concentrations and Mg/Ca ratio on calcium carbonate precipitation induced by heterotrophic aerobic bacteria, batch culture experiments were conducted with the bacterial strain Bacillus sp.5C-1, isolated from a Karst Cave and Bacillus thermoamylovorans, isolated from the sewage of Daqing Oilfield.Firstly,5C-1and5C-2were cultured in the PW medium at36℃,170rpm and40℃,170rpm respectively. At25℃, the experiments about5C-1with different concentration of SO42-(0,0.2,1.0,3.0,15.0and29.0mmol/L) were conducted to discuss the impacts of SO42-on the precipitation induced by5C-1. A series of solutions of5C-1were sampled at24,27,54and108hours finding that the environmental conditions changed along the time. The increasing pH (7.82,8.02,8.33and8.80) and OD at421nm (0.686,0.840,1.292and1.331) indicate that the growth status of5C-1would be gained for precipitation. After6hours, the remaining concentrations of SO42-and Ca2+were examined to evaluate the ability of5C-1to precipitate CaCO3. It is demonstrated that heterotrophic aerobic bacteria5C-1mediate direct precipitation of calcium carbonate under conditions with various concentration of SO42-, and low SO42-concentrations are better for precipitation rate and speed if compared. The present of sulfate does not inhibit dolomite precipitation at low concentrations of SO42-but at high SO42-concentrations the precipitation role of5C-1is weakened especially the role of metabolites and nucleation sites on the cell surface of5C-1. On the other hand, the CaCO3precipitation experiments under controlled25℃and various Mg/Ca ratio (3,5,7,8) of the thermophilic aerobic Bacillus thermoamylovorans5C-2was conducted to evaluate the impacts of Mg/Ca on the precipitation induced by5C-1. Several samples of5C-2with pH (8.90) and OD (1.272) at421nm were taken at48h. The experimental design consisted in cells were removal by6000-rpm centrifugation for15min in Group A, having the Group B as control in which no treatment was applied. After a24-hour precipitation, the precipitates collected by centrifugation at9000rpm for5min were lyophilized and weighed and the selected precipitates were analyzed by X-ray Diffraction (XRD) and Scanning Electronic Microscope (SEM) finding that Mg/Ca ratio has different impacts on dolomite formation ability of5C-2and at high Mg/Ca ratio the precipitation rate of dolomite is weakened. Only group B without removing5C-2mediate mineral similar to dolomite with Mg/Ca=1.01while the precipitates produced in group A with the removal of bacteria were observed as calcite with Mg and Mg/Ca was close to0.81.All experiments were run in duplicates and data presented here were the average of the duplicates. Meanwhile, a set of abiotic controls was also conducted for comparison.