Combining microbially induced calcite precipitation (MICP) with zeolite: A new technique to reduce ammonia emission and enhance soil treatment ability of MICP technology

The byproduct ammonia limits the wide application of the urea-hydrolysis based microbially induced calcite precipitation (MICP) technique. Here, we proposed a new technique termed the “MICP-zeolite technique” to reduce ammonia emission, which combined ammonia removal by zeolite with the MICP process. To understand the new technique, 1) the ability of the used zeolite to adsorb bacteria and remove ammonia was tested; 2) the MICP and MICP-zeolite techniques were applied to soils via both a mixing way and an injecting way to evaluate their performance in ammonia emission, soil cementation, and permeability reduction; 3) many properties of the zeolite and treated/untreated sands were characterized including surface charge, microstructure, surface area, pore size distribution. The results present that the zeolite can adsorb Sporosarcina pasteurii strongly, due to its larger specific surface area, rougher and outwardly-protruding surface, and less negative charge. Contact time, pH, temperature, and zeolite dosage affected ammonia removal efficiency. The MICP-zeolite technique resulted in less ammonia emission, greater soil strength, and lower permeability, and the injecting way is more effective in soil cementation. In soils treated by the proposed technique, the clogged pores were more, the precipitated crystals were more and smaller, the number of micropores and macropores reduced more, and the zeta-potential of particles increased more. Collectively, the MICP-zeolite technique is superior to the MICP technique in treatment effect and environmental friendliness.