Influencing factors and formation mechanism of CaCO3 precipitation induced by microbial carbonic anhydrase

Microbial carbonic anhydrase promotes carbonate deposition, which is important in the formation and evolution of global carbon cycle and geological processes. A kind of bacteria producing extracellular carbonic anhydrase was selected to study the effects of temperature, pH value and Ca2+ concentration on bacterial growth, carbonic anhydrase activity and calcification rate in this paper. The results showed that the activity of carbonic anhydrase at 30 degrees C was the highest, which was beneficial to the calcification reaction, calcification rate of CaCO3 was the fastest in alkaline environment with the initial pH value of 9.0. When the Ca-2(+) concentration was 60 mM, compared with other Ca2+ concentration, CA bacteria could grow and reproduce best, and the activity of bacteria was the highest, too low Ca-2(+) concentration would affect the generation of CaCO3, while too high Ca-2(+) concentration would seriously affect the growth of bacteria and reduce the calcification rate. Finally, the mechanism of CaCO3 precipitation induced by microbial carbonic anhydrase was studied. Carbonic anhydrase can accelerate the hydration of CO2 into HCO3-, and react with OH- and Ca2+ to form CaCO3 precipitation in alkaline environment and in the presence of calcium source.