Current construction sector is facing the challenge of non–sustainability due to huge production of greenhouse gases and consumption of large amounts of materials and energy. On the other hand, Nature has been synthesising sustainable and durable materials in ambient conditions in carbon neutral way for millions of years, via microbially induced mineralization as seen in natural formations of rocks, caves, coral reefs, stromatolites etc. Learning from Nature and mimicking natural processes by harnessing microbially induced carbonate precipitation (MICP) for engineered structures and building materials holds the key solution to sustainability challenge.
MICP has recently emerged as promising soil improvement technique for several civil engineering applications. In situ applications are performed either by augmenting carbonate precipitating bacteria or stimulating such indigenous bacteria. Two major pathways through which bacteria have been successfully reported to produce durable calcium carbonates are through ureolysis and carbonic anhydrase production. In the current study biostimulation and bioaugmentation in soils for carbonate precipitation via these routes was investigated for a period of three months. Significant changes in indigenous bacterial populations following biostimulation were seen in both pathways at different time intervals. Bioaugmented bacterial isolates were seen to survive along with native bacterial populations initially but at later time intervals, native populations were seen dominating which highlights importance of stimulation over augmentation in large scale applications. In regards to carbonate precipitation potential, higher precipitation was seen through bioaugmentation using ureolytic pathway initially followed by biostimulation of ureolytic bacteria although production of ammonia in both routes need further attention. At later time intervals, stimulation of ureolytic populations was found to perform better in relation to ureolysis and carbonate production. Efficient carbonate precipitation through bioaugmentation and biostimulation via carbonic anhydrase producing bacteria was also seen, though this process was slightly slower compared to ureolytic. The results suggest that biostimulation via ureolysis and CA bears potential for biocementation but its efficacy may vary depending upon initial microbial abundance and nutrient conditions.