Experimental Optimization of Microbial-Induced Carbonate Precipitation for Soil Improvement

Implementation of laboratory-tested biomediated soil improvement techniques in the field depends on upscaling the primary processes and controlling their rates. Microbial-induced carbonate precipitation (MICP) holds the potential for increasing the shear stiffness and reducing the hydraulic conductivity by harnessing a natural microbiological process that precipitates calcium carbonate. The study presented herein focuses on controlling MICP treatment of one-dimensional flow, half-meter-scale column experiments. Treatment was optimized by varying procedural parameters in five pairs of experiments including flow rates, flow direction, and formulations of biological and chemical amendments. Monitoring of column experiments included spatial and temporal measurements of the physical, chemical, and biological properties essential to the performance of MICP, including shear wave velocity, permeability, calcium carbonate content, aqueous calcium, aqueous ammonium, aqueous urea, and bacterial density. Relatively uniform improvement of a half-meter one-dimensional flow sand column experiment resulted in a change from a shear wave velocity of 140 m/s to an average of 600 m/s. Examination of data sets provides insight into which parameters have a first-order effect of MICP treatment uniformity and efficiency and how these parameters can be monitored and controlled.