Modeling U(VI) biomineralization in single- and dual-porosity porous media

Uranium extraction, processing, and storage have resulted in a legacy of uranium-contaminated groundwater aquifers worldwide. An emerging remediation technology for such sites is the in situ immobilization of uranium via biostimulation of dissimilatory metal-reducing bacteria (DMRB). While this approach has been successfully demonstrated in experimental studies, advances in understanding and optimization of the technique are needed. The motivation of this work was to understand better how dual-porosity (DP) porous media may affect immobilization efficiency via interactions with the dominant geochemical and microbial processes. A biogeochemical reactive transport model was developed for uranium immobilization by DMRB in both single- and dual-porosity porous media. The impact that microbial residence location has on the success of biostimulated U(VI) immobilization in DP porous media was explored under various porosity and mass transfer conditions. Simulations suggest that DP media are likely to show delayed U(VI) immobilization relative to single- porosity systems. U(VI) immobilization is predicted to be less when microbial activity is restricted to diffusion-dominant regions but not when restricted to advective-dominant regions. The results further highlight the importance of characterizing the bioresidency status of field sites if biogeochemical models are to predict accurately remediation schemes in physically heterogeneous media.