The challenge of ammonia free soil bio-cementation and recent breakthroughs: A review of phospate minerals for soil biocementation

In biogeotechnical research, microbial induced calcium carbonate precipitation (MICP) technique has emerged as an effective means of enhancing soil engineering. Through the microbial activity, MICP application has produced several benefits such as enhancing the bearing capacity of soil, stabilizing slopes, liquefaction mitigation, and preventing erosion in geotechnical engineering. To date, ureolysis based metabolic process of urease producing bacteria is the most widely used approach due to rapid and controlled precipitation of calcium carbonate as a cementing agent in soil improvement. Despite significant developments with ureolytic-based MICP, ammonia production (NH4+ (aq) & NH3 (g)) due to enzymatic hydrolysis of urea is still a major issue posing threat to underground water and environment. In this comprehensive review, phosphate biomineralization as an alternative and efficient breakthrough in ammonia free bio-cementation is presented. Phosphate biomineralization approach will give direction towards the up scaling of soil improvement.