Precipitation of Carbonates Crystals by Bacteria Isolated from a Submerged fixed-film Bioreactor used for the Treatment of urban Wastewater

The precipitation of calcium carbonate by bacteria isolated from submerged fixed-film bioreactor used for the treatment of urban wastewater in both natural and artificial media was studied. However, carbonate precipitation was detected only when the bacteria grow in media added with calcium. Precipitation took place rapidly, and crystal formation began 3 d after inoculation and the percentage of carbonate-forming bacteria was slightly higher than 90%. Seventeen dominant colonies with carbonate precipitation capacity were the dominant heterotrophic platable bacteria growing aerobically in media added with calcium acetate and calcium chloride. According to their taxonomic affiliations (based on partial sequencing of the 16S-rRNA), the seventeen strains belonged to the following genera of Gram-positive and Gram-negative bacteria: Artrobacter, Bacillus, Enterococcus, Pseudomonas, Agromyces and Rhodococcus. All of these strains formed calcium carbonate crystals, precipitated always as calcite crystals which showed large amounts of bacterial fingerprints or bacteria calcification. In addition all the seventeen bacterial strains showed carbonic anhydrase activity. The results of this research suggest that in submerged fixed-film bioreactors used for the treatment of urban wastewater, the precipitation of carbonates through bacterial action could take place in situ in the presence of certain concentrations of calcium. Moreover, this biological activity could be useful in the CO2 and calcium capture in urban wastewater treatments.