Life Cycle Sustainability Assessment of Microbially Induced Calcium Carbonate Precipitation (MICP) Soil Improvement Techniques

Microbially induced calcium carbonate precipitation (MICP) is a biomediated ground improvement technology that uses ureolytic bacteria to precipitate calcium carbonate minerals to improve the strength and stiffness of soils. MICP can be mediated by either augmented non-native or stimulated indigenous microorganisms, resulting in biocemented soils and generated aqueous ammonium (NH4+) byproducts. Although the process has been extensively investigated, the fate and transport of generated NH4+ byproducts has posed an environmental challenge and to date, their associated environmental impacts have remained poorly understood. In an effort to better quantify process impacts, a large-scale experiment was conducted involving three 3.7 m long soil columns, wherein three different ureolytic biocementation treatment approaches were employed. A life cycle sustainability assessment (LCSA) was performed to compare the environmental impacts and costs of these different MICP treatment approaches as well as evaluate the potential environmental benefits of NH4+ byproduct removal using post-treatment rinsing. The objective of this paper is to present the results of the LCSA study. LCSA results suggest that when treatments are consistent with those performed in this study, stimulation can be more sustainable than augmentation, and the use of lower ureolytic rates can further reduce process environmental impacts by achieving greater spatial uniformity and extent of biocementation. The LCSA outcomes also illustrate tension between the environmental benefits afforded by NH4+ byproduct removal and the life cycle impacts and costs associated with this removal. For the specific testing conditions, the injection of 1.8 pore volumes of rinse solutions to remove generated NH4+ byproducts following biocementation was found to minimize environmental impacts; however, further refinement of such approaches will likely result from future field-scale applications.