Ureolytic bacteria for MICP application to iron-rich slag materials for waste stabilization and carbon sequestration

Microbial induced carbonate precipitation (MICP) is a novel soil and cement strengthening technique for civil and geotechnical engineering fields. Recently emerging is the use of MICP as a biological remediation strategy to immobilize contaminants, strengthen metalliferous waste, and sequester carbon dioxide from mining activities. MICP has a broad spectrum of benefits, but application of bacteria species to inhospitable mining wastes is challenging. Most studies applying MICP to metal and/or metalloid contaminated waste utilize a biostimulation approach. This is not always feasible based on the toxic nature of the waste. This study evaluated the ecotoxicity of 2 iron-rich slag materials prior to bacterial screening and enrichment. S1 showed bacterial toxicity but not plant toxicity, while S2 showed high bacterial and plant toxicity. Bacterial screening found a lack of significant DNA in both iron-rich slag materials. Bacterial enrichment was able to stimulate growth of Bacillus cereus (PZ013063.1) from S1, while S2 remained sterile after 1-cycle of enrichment. Stimulated Bacillus cereus was compared to exogeneous, ureolytic Sporosarcina pasteurii, in which the latter showed higher bacterial growth and tolerance to a wider range of environmental conditions. Furthermore, since Bacillus cereus exhibited phenotypic heterogeneity of the urease gene during isolation, bioaugmentation using Sporosarcina pasteurii for MICP application to iron-rich slag materials is recommended.