Operando Studies of Iodine Species in an Advanced Oxidative Water Treatment Reactor

Abstract

We present an electrochemical advanced oxidation process (eAOP) reactor employing expanded graphite, potassium iodide (KI), and electrical current, which demonstrates an exceptionally high rate of inactivation of E. coli (10 6 or 6log 10 reduction in viable cells) at low current density (0.12 mA/cm 2 ), with low contact time (5 minutes) and low concentration of KI (10 ppm; 0.06 mM)). Operando X-ray fluorescence mapping is used to show the distribution of iodine species in the reactor, and operando X-ray absorption spectroscopy in the anodic chamber reveals iodine species with higher effective oxidation state than IO 4 -. Operando electrochemical measurements confirm the conditions in the anodic chambers are favourable for the creation of highly oxidized iodine products. The killing efficiency of this new eAOP reactor far exceeds that expected from either traditional iodine-based electrochemical water treatment or advanced oxidation systems alone, a phenomenon that may be associated with the production of highly oxidized iodine species reported here.

Review—Understanding and Controlling Charge Functions in Materials for Electrochemically Mediated Water Treatment

“…20,21,92,93 From structural to functional imaging.-Several advanced operando imaging tools have been developed to interrogate the structural evolution of charge-functional materials during electrochemical operations for water treatment such as heavy metal removal 40 and disinfection. 94 A recent study reported PVF-CNT for the electrochemical removal of chromium and arsenic oxyanions from water and utilized in situ TEM to directly visualize the nanoscale structure evolution of the PVF film during ions uptake and release processes in a liquid cell. 40 In the imaging set up, a tungsten electrode on the top chip served as counter electrode and a gold electrode on the bottom chip served as the working electrode (Fig.…”

“…Another study by Moustafa et al 94 demonstrated the use of operando X-ray fluorescence mapping (XRF) to image the distribution of iodine species in an EAOP reactor, which was for inactivation of Escherichia coli in water (Fig. 4d).…”

“…In this review article, we elucidate the design principles of charge-functional materials for electrochemical mediated water treatment by considering fundamental performance-governing processes, including charge transport, surface adsorption, bulk ion insertion and (photo)electrocatalysis. We also highlight the recent developments of in situ operando imaging tools, 40,94,95,[99][100][101]109 that probe these critical processes that occur during water treatment. The field of electrochemical mediated water remediation is still at its infancy (except for CDI), and the full potential of related technologies has yet to be released.…”

“…The applications of in situ operando characterization techniques to probe electrochemical water treatment processes are still relatively rare, with an only handful of examples demonstrated recently. 40,94,95 In situ TEM was utilized to directly visualize the nanoscale structure evolution of the PVF film during chromium and arsenic oxyanions uptake and release processes, providing direct evidence of the redox driven anion insertion into PVF film. 40 Operando X-ray fluorescence mapping was utilized to image the distribution of iodine species in the reactor during inactivation of Escherichia coli in water, demonstrating the anodic chambers are favorable for the creation of highly oxidized iodine products.…”

“…40 Operando X-ray fluorescence mapping was utilized to image the distribution of iodine species in the reactor during inactivation of Escherichia coli in water, demonstrating the anodic chambers are favorable for the creation of highly oxidized iodine products. 94 A novel competition-enabled imaging technique with super-resolution (COMPEITS) was developed to probe the photoelectrocatalytic oxidation of hydroquinone (HQ), a micropollutant in water, on BiVO 4 catalyst particles, revealing stronger HQ adsorption on the {010} facet than the {110} facet, and weaker at the corner. 95 In addition to these previously documented research efforts, we envision there exist exciting opportunities to employ the in situ operando imaging to reveal previously unknown fundamental mechanisms in charge-functional materials for water treatment.…”