Abstract
The invention of microorganism’s involvement in carbonate precipitation, has lead the exploration of this process in the field of construction engineering. Biocement is a product innovation from developing bioprocess technology called biocementation. Biocement refers to a CaCO3 deposit that formed due to microorganism activity in the system rich of calcium ion. The primary role of microorganism in carbonate precipitation is mainly due to their ability to create an alkaline environment (high pH and DIC increase) through their various physiological activities. Three main groups of microorganism that can induce the carbonate precipitation: (i) photosynthetic microorganism such as cyanobacteria and microalgae; (ii) sulphate reducing bacteria; and (iii) some species of microorganism involved in nitrogen cycle. Microalgae are photosynthetic microorganism and utilize urea using urease or urea amidolyase enzyme, based on that it is possible to use microalgae as media to produce biocement through biocementation. This paper overviews biocement in general, biocementation, type of microorganism and their pathways in inducing carbonate precipitation and the prospect of microalgae to be used in biocement production.
Highlights
Construction engineering consumes a large amount of materials from non-renewable resources, which most of the materials contribute CO2 emission to the air at their production or application stage
The precipitation of calcium carbonate (CaCO3) may be performed due to microorganism activity and it produces massive limestone or small crystal forms [3]. These deposit of calcium carbonate known as biocement or microbial induced carbonate precipitation (MICP) [3,4]
Biocement has many advantages compared to an ordinary cement, such as: the production process is slightly different with sandstone production, biocement need a much shorter time; it is suitable for in-situ process; raw material of biocement are produced at low temperature, more efficient compared to an ordinary cement which used temperature up to 1500 ̊C in production process; biocement can be used as ecoconstruction material since it consume less energy and less CO2 emission in the production process rather than other ordinary cement [3,5]
Summary
Construction engineering consumes a large amount of materials from non-renewable resources, which most of the materials contribute CO2 emission to the air at their production or application stage. Carbon dioxide consumed by photosynthetic microorganisms shift the equilibrium and resulting the increment of pH (equation 3) [7] When this reaction occurs in the present of calcium ion in the system, calcium carbonate is produced as described at chemical reaction in equation 4 [6]. The hydrolysis of urea by urease enzyme in heterotrophic microorganism will produce carbonate ion and ammonium This mechanism will result system with higher pH and rich of carbonate ion [12]. Biocementation is a process to produce binding material (biocement) based on microbial induced carbonate precipitation (MICP) mechanism. This process can be applied in many fields such as construction, petroleum, erosion control, and environment. Calcium carbonate precipitation occur in nature following several process such as: (i) abiotic chemical precipitation from saturated solution due to evaporation, temperature increase and/or pressure decrease; (ii) production of external and internal skeleton by eukaryotes; (iii) CO2 pressure derivation under effect of autotrophic processes (photosynthesis, methanogenesis); (iv) fungal mediation;
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