Anodic Oxidation of Organic Contaminants Using Fixed and Flow Electrodes

The presence of persistent organic pollutants in water/wastewater has caused a rising public concern and become a major issue for the sustainable development of society. Electrochemical advanced oxidation processes (EAOPs), which can ultimately mineralize recalcitrant organic compounds to CO2 and H2O, have attracted increasing interest in recent years. While many studies have been conducted on the oxidation effectiveness of a wide variety of organic compounds using various anodes, more efforts should be paid on understanding direct electron transfer (DET) and •OH generation mechanisms in anodic oxidation systems to facilitate the design of electrochemical oxidation systems and decrease the energy consumption. In this thesis, DET and •OH generation mechanisms are investigated using fixed and flow electrodes in different electrochemical oxidation systems. A review of recent progress in understanding the DET and •OH generation mechanisms of the most commonly used anodes is followed by studies on the impact of the presence and state of carbon-containing materials on fixed TinO2n-1 electrodes. There has been considerable recent interest in use of electrodes constructed from this conducting material with studies of DET processes in a traditional flow-by cell showing that the oxygen-containing functional groups play an important role in interfacial electron transfer. In addition to studies on TinO2n-1 fixed electrode systems, attention has also been given to development and use of a novel flow anode system in which a suspension of TinO2n-1 is used as a “flow anode” with the particles charged via contact with the anode current collector. Initial studies focussed on the oxidation of H2O to adsorbed OH* at only 1.5 V vs SHE with the ability to perform oxidation of organic target compounds at this low potential suggesting that flow anodic oxidation represents a viable electrochemical technology for water decontamination. Following studies of the indirect oxidation of organic compounds via generation of adsorbed OH*, we investigated DET processes in the flow anode system in a configuration in which carbon black was utilized as the flow anode material. The results indicate that the potential drop and mass transfer processes at the solid-liquid interfaces play critical roles in DET processes in such suspension systems. Finally, the long-term performance of a continuously operated flow anode system with particles retained in the system using an ultrafiltration membrane (UF). Results showed that the flow anode/UF system was capable of continuously oxidizing perfluorocarboxylic acid for 12 days with a high efficiency and a reasonable energy consumption compared to other technologies