Microbially Induced Calcite Precipitation via Microbial Organic Acid Oxidation

Abstract

Microbially Induced Calcite Precipitation (MICP) or biocementation can improve the engineeringproperties of granular soils through the precipitation of calcium carbonate minerals on particle contacts and surfaces. The process has received significant research attention for a variety of different geotechnical applications including the mitigation of earthquake-induced soil liquefaction and surficial soil stabilization. Although most commonly this process is accomplished using microbial urea hydrolysis, other microbial metabolic pathways can be used to enable biocementation with the potential to eliminate the generation of ammonium by-products. Microbial organic acid oxidation (MOAO) presents one alternative pathway by which increases in solution carbonate species can be generated to enable calcium carbonate mineral formation. While past studies have considered the potential of this particular microbial pathway to enable biocementation for surficial applications, to-date few studies have investigated the feasibility of this pathway towards addressing deeper subsurface geotechnical applications wherein oxygen is iv more limited. In this study, small-scale batch and centimeter-scale column experiments were employed to explore the ability of microbial organic acid oxidation to enable biocementation soil improvement under conditions more representative of subsurface locations. Experiments investigated the potential of both microbial acetate and citrate oxidation to mediate biocementation as well as the effect of differences in treatment techniques including the methods used to supply dissolved oxygen, differences in solution compositions including the effect of supplied growth factors and bicarbonate salt additions, and differences treatment injection sequences. Results suggest that indigenous microorganisms can be enriched in natural sands to oxidize organic acids in the presence of calcium and bicarbonate salts under specific treatment conditions, thereby enabling the precipitation of calcium carbonate and other mineral by-products, with consequential increases in shear wave velocity. However, oxygen availability and solution bicarbonate additions may be a critical factor governing process success, with the contribution of abiotic precipitation mechanisms meriting further investigation.