Bio-Induced Calcite, Iron, and Manganese Precipitation for Geotechnical Engineering Applications

Bio-augmentation research with applications to geotechnical engineering has recently focused on introducing foreign bacteria into soil to precipitate minerals or produce biofilms. Urease producing bacteria have shown promise for inducing calcite precipitation which cements soil particles together and increases soil stiffness and strength. As an alternative to introducing foreign bacteria into soil, indigenous bacteria already present in the soil may be used to induce mineral precipitation. We have collected soil samples from various sources, each containing urease positive indigenous bacteria. Our experiments have demonstrated that these indigenous bacteria can be used to induce calcite precipitation of sufficient quantity to modify engineering soil properties. In addition to work with indigenous bacteria that induce calcite precipitation, we have conducted experiments using the bacteria Leptothrix discophora which induces iron and/or manganese mineral precipitation. A series of column tests have been performed to identify conditions that lead to increased iron and manganese mineral precipitation. Since Leptothrix discophora is known to induce iron precipitation during construction dewatering, we anticipate iron/manganese mineral precipitation can also be induced at some sites using indigenous bacteria. Results from our experiments to date show that biomineralization is a promising technology for modifying engineering soil properties and mitigating geologic hazards.