Invited Lecture – Field scale implementation and commercialization of bio-based ground improvement technologies
More than two decades of research on bio-based ground improvement has highlighted several potential engineering applications. Bio-based ground improvement involves the use of micro-organisms to catalyze biochemical reactions that improve the geomechanical properties of soils. The three main products of these biochemical conversions are biominerals, biogas and biomass. The most intensively studied biochemical reaction is microbially induced calcium carbonate precipitation (MICP) by urea hydrolysis. In this process ureolytic bacteria are either injected or stimulated in the ground by injecting a nutrient solution which selectively enriches indigenous ureolytic micro-organisms. Consequently, the ureolytic bacteria are supplied with a solution containing urea and calcium chloride. Hydrolysis of urea results in the precipitation of calcium carbonate, increase the strength, stiffness and dilatancy or reduce compressibility and permeability of coarse granular soils. The by-product ammonium chloride needs to be removed. The potential of MICP has been evaluated for various applications, including mitigation of wind and water erosion, liquefaction mitigation, slope stability, co-precipitation of contaminants, permeable reactive barriers and carbon dioxide sequestration by well clogging. Alternative processes have received less attention, but may be just as promising. One of these processes is microbially induced desaturation and precipitation (MIDP) by nitrate-reducing bacteria. In this process indigenous nitrate-reducing bacteria are stimulated by injecting a solution containing calcium, nitrate and acetate (or another form of dissolved organic carbon). Main products of this biochemical conversion are nitrogen gas and calcium carbonate. SImilar to urea hydrolysis, oxidation of organic carbon by nitrate-reducing bacteria can increase the strength and stiffness of granular soils. The formation and entrapment of nitrogen gas desaturates the soil and increases the compressibility of used to suppress pore pressure build up during cyclic loading and can mitigate earthquake-induced liquefaction. The third product, biomass or biopolymers can also increase the erosion resistance of soils and studies have been performed on restoration of biocrust by stimulating carbon sequestering micro-organisms. This contribution highlights the achievements so far towards field scale implementation of bio-based ground improvement technologies and addresses the challenges towards commercialization, and opportunities for new research.