Precipitation of carbonates by bacteria isolated from wastewater samples collected in a conventional wastewater treatment plant

This research studied the precipitation of calcium carbonate by populations of bacteria from domestic wastewater cultivated in both natural and artificial solid culture media. The only carbonate-forming bacteria detected appeared in an artificial medium added with calcium acetate. Precipitation occurred three days after inoculation, and the percentage was slightly higher than 65 %. Our results showed that nine major carbonate-forming colony types were the dominant heterotrophic platable bacteria growing aerobically in artificial media added with calcium acetate. According to their taxonomic affiliations (based on partial sequencing of the 16S-rRNA), the nine strains belonged to the following nine genera of Gram-negative and Gram-positive bacteria: Caulobacter, Blastomonas, Roseobacter, Staphylococcus, Bacillus, Gemmatimonas, Saccharopolyspora, Microthrix, and Sphingomonas. All of these strains formed calcium carbonate, precipitated as calcite and vaterite in different proportions and shapes (spheres, hemispheres, dumbbells, and pseudopolyhedral forms). The results of this study suggest that in real domestic wastewater, the precipitation of carbonates through bacterial action could not take place in situ because the concentrations of calcium did not create the optimal circumstances for biomineralization. However, in the artificial media, it was possible to induce this process by adding calcium ions.