Authors: Sumit Kumar Dubey
Cement production needs high energy (temperature up to 1500°C) and emit carbon dioxide (CO2) in the production process but bio-cement can be produced at ambient temperature by bioprocess as well as emit less carbon dioxide.
Biocement simply means the cement-like material which derived by biological cell (more precisely microbial cells). The production of biocement is based on the calcium carbonate (CaCO3) precipitation by microorganisms. Upon the literature survey, it has been found that photosynthetic microorganisms, sulfate-reducing bacteria (or archaea) and a group of microorganism involved in nitrogen cycle (may include fixation, ammonification, nitrification, and denitrification) can induce the CaCO 3 precipitation at high pH. Biocementation refers to the production of biocement by bioprocess technology.
Bio-cement production usually required microbial consortium which includes photosynthetic microorganisms (e.g. Cyanobacteria and Microalgae), sulfate-reducing bacteria (e.g. Deltaproteobacteria andFirmicutes) and the group of nitrogen recycling bacteria (e.g. Azotobacter and Rhizobium) for CaCO3 precipitation.
CaCO3 precipitation govern by following parameters:
1. Calcium concentration
2. Carbonate concentration
4. Presence of nucleation sites
The principle behind the production of bio-cement is a carbonate precipitation by a group microorganism at high pH (10.0 ± 1.0) and increased DIC (dissolved inorganic carbon). The mechanism of CaCO 3 precipitation is solely depended upon microbial metabolic activity. MCIP (Microbial Induced Carbonate Precipitation) process is initiated by photosynthetic microorganisms in the aquatic environments. Photosynthetic microorganisms consume CO2 in their metabolic process and pH of the medium is increased. Further, the calcium carbonate is produced in the presence of calcium ion in the medium. CaCO3 precipitation also induced by heterotrophic sulfate-reducing bacteria (SRB) organism. Urease enzyme activity has been used to induce the precipitation of calcium carbonate.
Reaction followed by Photosynthetic microorganisms for CaCO3 precipitation:
CO2 + H2O → (CH2O) + O2
2HCO3- ↔ CO2 + CO3 2- + H2O
CO32- + H2O ↔ HCO3 - + OH-
Ca2+ + HCO3- + OH- → CaCO 3 + 2H2O
The precipitation of CaCO3 (biocement) can be combined with other supporting material such as sand. Biocementation were also developed in the process of biological mortar production. Biological mortar consists of three main components such as limestone powder, nutrient and bacterial paste. Biocement was filled in concrete rift and investigated which showed the significant increment of strength and stiﬀness value compared with control.
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About Author / Additional Info:
Department of Biotechnology,
D.L.S. PG. College, Bilaspur 495001