New insights into the role of pH and aeration in the bacterial production of calcium carbonate (CaCO3).

Over recent years, the implementation of microbially produced calcium carbonate (CaCO3) in different industrial and environmental applications has become an alternative for conventional approaches to induce CaCO3 precipitation. However, there are many factors affecting the biomineralization of CaCO3, which may restrict its application. In this study, we investigated the effects of pH and aeration as the main two influential parameters on bacterial precipitation of CaCO3. The results showed that the aeration had a significant effect on bacterial growth and its rise from 0.5 to 4.5 SLPM could produce 4.2 times higher CaCO3 precipitation. The increase of pH to 12 resulted in 6.3-fold increase in CaCO3 precipitation as compared to uncontrolled-pH fermentation. Morphological characterization showed that the pH is an effective parameter on CaCO3 morphology. Calcite was found to be the predominant precipitate during aeration-controlled fermentations, while vaterite was mainly produced at lower pH (up to 10) over controlled-pH fermentations. Further increase in pH resulted in a morphological transition, and vaterite transformed to calcite at the pH ranges between 10 and 12.