Influence of Salt Stress Conditions on Calcite Formation by Calcifying Bacteria Isolated from Saline Environment

Abstract

Surface treatments play an important role in the protection of construction materials from the ingress of water and other deleterious substances. Due to the negative side effects of some of the conventional techniques, microbiologically induced calcium carbonate precipitation (MICCP) has been proposed as novel and environmental friendly strategy for the protection of buildings. Most of deterioration of buildings near sea coast takes place because of change in temperature, moisture, physical factors and chemical factors. The basic principles for MICCP are (1) the microbial urease that hydrolyzes urea to produce ammonia and carbonic acid (2) carbonic anhydrase that catalyzes the conversion of carbonic acid to bicarbonate ions which would be available for calcium carbonate precipitation (3) the ammonia released in surroundings subsequently increases pH, leading to accumulation of insoluble calcium carbonate. The technique can be used to improve the compressive strength and durability of cracked concrete of buildings near sea coast. The effect of different salt concentrations on calcite formation by calcifying halobacteria was studied and efficient calcification was observed in saline environments up to salt concentration 5% but above that calcium carbonate precipitation decreased. Scanning electron microscopy (SEM) analysis evidenced the direct involvement of microorganisms in CaCO3 precipitation.