Modeling of Electrochemical Oxidation of Contaminants in Porous Flow-Through Electrodes

This work developed a reactive-transport model to simulate electrochemical oxidation for water treatment applications. Newton’s method using finite difference was used to approximate the permeate concentrations, local overpotentials, and current densities of the equations. The electrochemical oxidation of perfluoroalkyl substances (PFAS) in porous flow-through electrodes was simulated, specifically perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS). A sensitivity analysis was performed to understand the effects of material and operating parameters on the removal of PFOA and PFOS along with the energy consumption. The parameters that related to electrode area (i.e., specific surface area, electrode thickness) had considerable sensitivity to performance metrics such as permeate concentration and energy consumption. Therefore, the sensitivity analysis could be used to determine the trade-offs between the material and operating parameters and the performance metrics. The reactive-transport model, experimental data, and density functional theory (DFT) simulations were used as a guide to understand and simulate the electrochemical oxidation pathways of wastewater contaminated with insensitive high explosives (IHEs), which included 2,4-dinitroanisole (DNAN), 3-nitro-1,2,4-triazol-5-one (NTO), and nitroguanidine (NQ). This was achieved by proposing mechanisms that described the degradation of PFAS and IHEs, implementing the mechanisms into the model, and using calibration of the model to experimental data to gain a better understanding of the probable oxidation pathways. The model included the generation of hydroxyl radicals (OH^•) and formation of reactive chlorine species (RCSs) because they played a role in the oxidation pathways of DNAN, NQ, and NTO. It was found that DNAN and NTO underwent direct electron transfer and reacted with OH^•. The oxidation of NQ led to polymerization reactions that caused blocking of the electrode surface but were reduced in the presence of NaCl due to reactions with RCSs. Obtaining a better understanding of the oxidation pathways of the IHEs will improve the model’s ability to act as a useful tool in remediating IHE-contaminated wastewater at Department of Defense sites.