Microbiological precipitation of CaCO3

The process of microbial mineral plugging in porous media is common in natu re. We examined physical and biochemical properties of CaCO3 precipitation induced by Bacillus pasteurii, an alkalophilic soil microorganism. X-ray di ffraction analysis quantified the composition of the mineral deposited in s and and identified the CaCO3 crystal as calcite. Examination by scanning el ectron microscopy identified bacteria in the middle of calcite crystals, wh ich acted as nucleation sites. The rare of microbiological CaCO3 precipitat ion correlated with cell growth and was significantly faster than that of c hemical precipitation. Biochemical properties of urease (urea amidohydrolas e, E.C. 3.5.1.5) from B. pasteurii that was indirectly involved in CaCO3 pr ecipitation were examined to understand the kinetics of the microbiological process. Urease from B. pasteurii exhibited a relatively low affinity for urea at pH 7.0 with a K-m of 41.6 mM and V-max of 3.55 mM min(-1) mg(-1) pr otein and increased affinity at pH 7.7 with a K-m of 26.2 mM and V-max of 1 .72 mM min(-1) mg(-1) protein. Results of kinetic studies indicate that ure ase activity and its affinity to urea are significantly high at the pH wher e calcite precipitation is favorable. Our findings further suggest a potent ial use of the microbial calcite precipitation process in remediation of th e surface and subsurface of porous media. (C) 1999 Published by Elsevier Sc ience Ltd. All rights reserved.