Laboratory Studies on Enzyme and Microbially Induced Carbonate Precipitation for Mitigation of Fugitive Dust from Saline Soil

The potential for biocementation by Enzyme and Microbial-Induced Carbonate Precipitation (EICP/MICP) via urea hydrolysis to reduce fugitive dust from saline sediments of the Salton Sea by formation of a biocemented crust was evaluated in a laboratory study. Shrinkage of the Salton Sea, a large, man-made inland lake, as a result of a prolonged drought and reductions in agricultural runoff due to water conservation has resulted in large playas (exposed sediments of the shoreline). Fugitive dust (wind-blown soil) from the exposed playa are a source of environmental and human health concerns. EICP and MICP technologies offer potentially sustainable and cost-effective mitigation methods for fugitive dust by forming a dust-resistant biocemented crust on the soil through the precipitation of calcium carbonate (CaCO3) cement. To evaluate the potential of EICP and MICP for fugitive dust mitigation, a laboratory testing program including elemental and mineralogical composition analyses, penetration testing, and carbonate content measurements was carried out on untreated and treated sediments from two locations on the lakeshore. Elemental and mineralogical composition analyses of the sediments showed soluble salt content (predominantly halite) of 4%–5% (by mass) for sediments recovered from the west side of the lake and 30%–45% for sediments recovered from the southeast side of the lake. The effectiveness of EICP and MICP was assessed experimentally by performing strain-controlled penetration tests on soil-filled pans treated by percolation of EICP and MICP solutions and by measuring the CaCO3 content of treated samples. The penetration tests showed that a crust was formed that increased the surface strength in all specimens. However, in the specimens with higher salt content, the calcium carbonate content did not show any significant increase following treatment and the penetration resistance of the specimens treated with EICP and MICP was comparable to the specimen treated with salt (after allowing the water to evaporate). On the other hand, in the specimens containing lower salt content, a carbonate crust was formed, and the surface strength of the specimens increased following EICP and MICP treatments. The lack of carbonate precipitation of the specimens of the high salinity soil is attributed to the dissolution of salts into the treatment solution, which suppressed the urease activity. This study illustrates an important constraint that must be considered when treating saline soils using EICP or MICP.