Development of a point-of-use water treatment system for organic contaminant degradation (2021)
Organic pollution of water is one of the most persistent types of impurities. In municipal water treatment plants, the degradation of organic compounds is achieved by advanced oxidation processes (AOPs), where the exposure of hydrogen peroxide (H₂O₂) containing influent to ultraviolet (UV) lamps converts H₂O₂ to hydroxyl radicals (·OH), which oxidize organic pollutants. However, the need to introduce a chemical (H₂O₂) and the use of bulky UV lamps prevent this process from being scaled down.In this study, an electrochemical cell was developed for the in situ generation of H₂O₂ from water and atmospheric oxygen using a two-electron oxygen reduction reaction (2e-ORR), thus eliminating the need for the external addition of H₂O₂. Moreover, the electrochemical reactor was equipped with novel UV sources, ultraviolet light-emitting diodes (UV-LEDs) with a wavelength of 277 nm, and microplasma lamps with wavelengths of 172 nm, 222 nm, and a broad spectrum of 220–280 nm. The electrochemical cell exhibited a high current efficiency of nearly 90% toward H₂O₂ production. The degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) and methylene blue (MB) was monitored based on various operational parameters. The performance of the system for electro-Fenton (EF) and photoelectro-Fenton (PEF) processes was studied using the three microplasma lamps. In all cases, the system exhibited high removal of the organic compounds (e.g., >70% of 2,4-D with UV-LEDs at the water flow rate of 50 mL min⁻¹).A gas diffusion electrode (GDE) was developed based on expanded polytetrafluoroethylene (ePTFE) substrate to produce H₂O₂. The GDE characterization indicated its tolerance to a pressure difference of >70 psi. The performance of the GDE for the cathodic generation of H₂O₂ was evaluated based on catalyst loading, electrolyte flow rate, and current density. The results indicated a direct relationship between the current and H₂O₂ production. Higher catalyst loading led to increased H₂O₂ production, while the concentration of H₂O₂ decreased with an elevated flow rate.In sum, the electrochemical photoreactor developed in this study demonstrated key advantages such as small footprint, low power consumption, and high contaminant degradation rate, making it suitable for point-of-use (POU) water treatment to eliminate both microbial and chemical contaminants.