Daniel Giammar Washington University in St. Louis
Chromium(VI) is a toxic contaminant that has been observed in private and public water supplies as well as in treated drinking water. Current drinking water standards are only applicable to total chromium, which can be present as chromium(VI) as well as the much less toxic form of chromium(III) that is even a nutrient at low concentrations. It is likely that new drinking water standards specific to chromium(VI) will be implemented, and iron electrocoagulation is a technology with the potential to achieve the low concentrations that may be required. In iron electrocoagulation a direct current is applied between two iron electrodes. One of the electrodes is oxidized to release iron(II) to solution, and this soluble iron(II) can directly reduce chromium(VI) or be oxidized to iron(III) to produce iron oxide solids on which chromium(VI) can be reduced and adsorbed. Iron electrocoagulation for chromium(VI) removal has multiple removal pathways that involve homogeneous and heterogeneous chemical reduction, adsorption, and co-precipitation. The primary objective of this research project is to advance the mechanistic understanding of chromium(VI) removal by iron electrocoagulation. The project will evaluate electrocoagulation performance over a broad range of water chemistry conditions in a laboratory-scale electrocoagulation reactor. Analytical methods will track changes in both total dissolved chromium and chromium(VI) to the very low levels that are being considered for regulations. The investigation will use advanced spectroscopic and stable isotope tools to identify the dominant reaction mechanisms occurring in the electrocoagulation reactor. X-ray absorption spectroscopy, which will be performed at national user facilities, will provide insights into the oxidation state and molecular-scale coordination of chromium associated with the solids generated in the reactor. Stable isotope fractionation of chromium can be diagnostic of specific reaction mechanisms. A mathematical model for electrocoagulation performance will integrate the mechanistic insights and data from the laboratory-scale experiments to enable predictions of performance over a broad range of conditions. The research will enable the optimal design of treatment strategies and accurate prediction of treatment performance for chromium(VI) removal.
This project will provide scientific information that will help improve the removal of hexavalent chromium, a contaminant of critical national interest, from drinking water. The research will determine the influence of water chemistry on the reactions involved in the process, which will enable the design of effective strategies for chromium(VI) removal for a broad range of drinking water sources. The research activities will determine reaction mechanisms of interest in environmental engineering as well as earth science and materials science. The project's overall application of spectroscopic characterization and stable isotope tools will advance the overall infrastructure for environmental engineering research. The educational and outreach components of the project will enhance graduate and undergraduate teaching and promote early student interest in science and engineering.
