A new method for controlling leaching through permeable channels

In the environment, natural cementation of geological formations occurs constantly over the geological time due to physical, chemical and biological reactions. Although much attention is devoted to these processes, awareness of microbial involvement in mineral consolidation is quite limited. Mineral precipitation is induced as a result of microbial metabolic activities and can persist as a part of the environment. Most deposits are identified as inorganic compounds such as CaC03, phosphorites, or sulfide, with a few organic compounds. These microbiologically induced substances are pollution-free, natural, and ubiquitous in all environments. The process of microbiologically induced mineral precipitation can be employed as a method of selective cementation of highly permeable structures in rock formations to reduce the porosity. The same process can also be used in containing contaminants. This option is studied in this paper. A series of experiments was conducted to investigate the possibility of using microbial plugging of highly permeable channels under various conditions. Results indicate that complete plugging (resulting in nil flow rate) can occur within days of nutrient injection in a sand packed column containing bacteria. The process is highly effective in the presence of fractures which appears to create new nucleation sites for capturing bacteria clusters, leading to improved selective plugging. Finally, a series of batch experiments was conducted to find an optimum pH for bacterial growth as well as mineral precipitation.