Calcium and magnesium ions removal by different bacteria strains: Implications for limitation of lime-scale formation during seawater desalination

Desalination of seawater has been recognized as an important source of freshwater. However, during the process, the lime-scale derived from the precipitation of Ca 2+ and Mg 2+ frequently blocks and corrodes the desalination equipment. Therefore, it is necessary to remove Ca 2+ and Mg 2+ ions. This study shows that Ca 2+ and Mg 2+ ions can be removed through extracellular and intracellular biomineralization. The results show that Bacillus licheniformis Y1 induced the precipitation of aragonite and Mg-calcite, whereas only monohydrocalcite precipitation was induced by Alkalibacillus salilacus WMS.1. Furthermore, the amounts of precipitate induced by B.licheniformis Y1 are higher than those of A.salilacus WMS.1. Our experimental results indicate that ∼96 % Ca 2+ and ∼50 % Mg 2+ ions precipitated induced by B.licheniformis Y1, while ∼75 % Ca 2+ and ∼16 % Mg 2+ removed by A.salilacus WMS.1 from solutions. Comparatively, the metabolism of B.licheniformis Y1 is more vigorous than A.salilacus WMS.1, which creates a more favorable environment for Ca 2+ and Mg 2+ ions precipitation. Furthermore, the EPS of B.licheniformis Y1 consist of abundant Asp, Glu and humic acid, which contain more than one –COOH functional group. The –COOH group deprotonates under alkaline condition, trapping cations to facilitate the precipitation of carbonate minerals, which accelerates the removal of Ca 2+ and Mg 2+ ions. Since these two bacterial strains were both derived from marine sediments, and no significant harmful substances were produced during the experiments, their environmental character can be used for cation removal from natural waters. This study may provide new insights into limiting the formation of lime-scale in seawater desalination to retard the corrosion of equipment.