PhD Thesis Presentation - Pulsed Electric Field (PEF) Applications in Tap Water Disinfection and Electrochemical Nitrate Reduction

The prevalence of antibiotic-resistant bacteria and their resistance genes in chemically disinfected municipal waters reveals the need for supplementary water disinfection technologies that can effectively disinfect the presently changing water composition. Pulsed electric field (PEF) disinfection is an alternative water disinfection system that uses a non-thermal irreversible electroporation mechanism which does not promote adaptive capacities on the bacterial cells. Unfortunately, its energy requirement makes it hard for it to economically compete with other alternative technologies. Incorporation of nanostructures on the PEF electrodes has been one of the resolutions to significantly enhance electric field (EF) at minimal energy input. This study began by simulating EF with varying nanostructure geometries and electrode gap distances. The results guided the preparation of a flow-through set-up, fitted with nanostructure-enhanced electrodes. Two types of electrodes were prepared: (1) platinum-sputtered, copper-deposited titania nanotubes (PtCuxOTiO2 NTs), and (2) platinum-sputtered, polydopamine-coated copper oxide nanowires (PtPDACuxO NWs). Multiple-cycle cyclic voltammetry (CV) tests showed PtPDACuxO NWs to be more stable, hence used as cathode in the PEF disinfection tests. The designed PEF disinfection system operating at 100V, 100Hz, 1ms, achieved >3 log (99.9%) reduction after two passes of Escherichia coli (K12)-contaminated tap water (~104 CFU mL-1 ) at a flux of 2.3 m3 h-1 m-2 , with a residence time of just 0.26s pass-1 .

Chemical contaminants like nitrates (NO3 - ) have also become widespread in our waters, in particular groundwater that receives runoffs from agricultural areas using nitrogen-based fertilizers. Excess NO3 - brings damaging environmental and health impacts, thus minimized in ways such as electrochemically reducing NO3 - to an inert (N2) and/or more usable form (NH3). However, this process is limited by low reduction rate, poor selectivity, and energy intensiveness. These concerns were addressed through PEF electrochemical reduction treatment with PtPDACuxO NWs cathodes. When cathodes decorated with PtPDACuxO NWs were used, a relative increase of 91.41% for NH3 formation and 32.33% for reduction gases were obtained after two hours of pulsing operation: -1.30V cathodic potential, 0.10V anodic potential, 90% duty cycle, and 0.2Hz. The PtPDACuxO NWs electrode’s performance was also tested in treating NO3 - -contaminated synthetic hard freshwater. It was found to be more energy efficient, i.e., uses only ~150-200 kWh m-3 (order of decrease in NO3 - concentration)-1 — one order lower in magnitude relative to its counterparts.