Calcifying Bacteria Mediated Cementation for Improvement of Building Materials

Abstract

Microbially induced calcium carbonate precipitation (MICCP) is a naturally occurring biological process in which microbes produce inorganic materials as part of their basic metabolic activities. The hydrolysis of urea by microbial urease has been found to generate carbonate ions without an associated production of protons. In the presence of calcium rich environment, calcium carbonate crystals are produced which form solid crystalline material. The evidence of ureolytic bacterial involvement in precipitation of carbonates is a new revolution in the field of industrial microbiology. The application of these bacteria for production of calcium carbonates has recently emerged as a method for protecting and consolidating decayed construction materials as carbonate crystals precipitated are highly coherent and durable. The objective of the present study was to explore calcifying bacterial diversity from alkaline soils, understand the actual function and role of bacteria in carbonate precipitation, investigate the survival of bacterial cells within the building materials and finally develop a technology for enhancing the durability of energy efficient, low cost building materials. Ubiquitous nature of bacteria makes them ideal candidates for isolating them from extreme environments. The bacteria were isolated from calcareous soils so that they have the ability to survive in alkaline environment of various building materials. In the present work, five ureolytic and calcifying bacteria were isolated and characterized for production of various polymorphs of calcium carbonates. Role of enzymes urease and carbonic anhydrase in calcium carbonate precipitation were investigated and most efficient calcifying bacteria Bacillus megaterium SS3 was employed to improve the durability of various energy efficient building materials and building materials produced from industrial by products. An attempt was also made to investigate the potential of fly ash as carrier for calcifying bacterial cells for industrial applications of these builder bacteria. Optimum conditions for carbonate precipitation were also explored. Several calcifying bacterial strains were isolated from different soils and it was found that along with urease, carbonic anhydrase enzyme also plays important role in calcium carbonate precipitation. Different bacterial isolates precipitated different carbonate polymorphs revealing strain specific precipitation by these builder bacteria. The supplementation of calcifying bacterial cells led to positive effect on strength, porosity, permeability and durability of various low energy building materials and building materials produced from industrial by - products. The coherent and impervious nature of biological carbonates has been established from the present work. The results of present study also proved the potential of fly ash as a carrier for calcifying bacterial isolates. The current study uncovered several aspects of the bacterially induced carbonate precipitation and elucidated that production of “carbonate crystals” by calcifying bacteria is environmentally safe and novel technology to improve the durability of low energy buildings and answer to long quest for efficient building materials.