Upscaling of Reactive Transport Equations in Porous Media; Biologically Mediated Iron Reduction, and the Effect of Humic Materials on the Scaling Process

Princeton University, Princeton NJ

Investigators

Abstract

0337687 Jaffe Iron reduction affects many important porous media processes (i.e., sorption of compounds such as phosphates or arsenate, or the reduction of uranium, which occurs simultaneously with iron reduction) therefore predictive capabilities of iron reduction dynamics are needed and are the focus of this project. Iron reduction can be enhanced by the presence of humic substances that can act as an electron schedule, allowing the reaction to happen even when the iron reducer is not in direct contact with the iron surface. By focusing on iron reduction in the presence and absence of dissolved humic substances, this research will gain an insight on how humic substances affect the overall iron reduction kinetics. It will also provide a unique experimental system where (i) the reaction is dependent on the biomass of the iron reducing bacteria directly in contact with the iron surface (no humics), and (ii) all biomass of the iron reducing bacteria is involved in the reaction, subject to the transport limitations of the electron schedule process (with humics), and for which new scaling equations should apply. We will conduct a series of column experiments in quartz sand with varying iron distributions, and acetate as the carbon source. The columns will be seeded with an iron reducer and will be run in duplicate, with AQDS (a humic substance analog) and without AQDS. Bulk reaction rates will be obtained for all column experiments, and compared to the rates obtained via the scaling procedure. Results of this research can be transferred, for example, to model simulations of the biogeochemical dynamics in wetlands, groundwater trace metal/radionuclide remediation, arsenate and phosphate stability. This research will involve a part-time postdoctoral fellow, as well as graduate and undergraduate students, and will result in the development of an experimental module focused on biogeochemical reactions in soils for high school biology and chemistry teachers.