Studying the Relationship Between Indigenous Microbial Communities, Urease Activity, and Calcite Precipitation in Artificial Mixes of Clay and Sand

Microbial-induced calcium carbonate precipitation (MICP) is evolving as a new method of improving the mechanical properties of soil. This environmentally friendly technique is a bio-geo-chemical process where microbes play a key role in increasing soil strength through precipitating calcium carbonate. Past studies at Boise State University have indicated that MICP via bio-stimulation could be a viable alternative for expansive clayey soil treatments. However, these studies raised a new question about the relationship between soil composition, urease activity, and calcite precipitation. To answer this question, batch studies were conducted using autoclaved-sterilized sand mixed with different percentages of non-sterile natural clay and tested for urease activity. Moreover, to investigate the difference in urease activity between sand and clay bacterial communities, experiments were repeated on samples with different amounts of non-sterile sand and autoclaved-sterilized clay. MICP-treated clay/sand mixes were then evaluated for calcite precipitation. Our results showed that soil mixes with higher clay content have more urease activity and higher levels of calcite precipitation for both sand-autoclaved and clay-autoclaved soil mixes. Test results indicate that urease activity could potentially be used as an indicator of MICP performance in different soil compositions.