A novel UV-LED hydrogen peroxide electrochemical photoreactor for point-of-use organic contaminant degradation

Abstract

The degradation of organic contaminants is typically achieved by exposure of hydrogen peroxide (H₂O₂) containing influent to ultraviolet (UV) lamps as the source of radiation that can convert H₂O₂ to hydroxyl radicals (·OH), which oxidize organic pollutants. However, two factors prevent this process from being scaled down: the need to introduce H₂O₂, which requires special handling, and the use of bulky UV lamps, which have a high electric power consumption. In this work, an electrochemical cell was developed for the efficient in situ generation of H₂O₂ from water and atmospheric oxygen in a process called a two-electron oxygen reduction reaction (2e-ORR), so that the external addition of H₂O₂ is no longer needed. Moreover, the electrochemical cell was equipped with ultraviolet light-emitting diodes (UV-LEDs) to convert H₂O₂ to ·OH. The reactor exhibited a current efficiency of ∼90% for the H₂O₂ production at a flow rate of 50 mL min^-1. The degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) was studied at 277 nm based on different operational parameters, such as UV fluence rate, initial concentration, and initial pH. A high degradation of >70% was obtained at a UV output of 900 mW. Our approach, the first of its kind, has novel features applied, including: optimal radiation distribution in the reactor by applying a new UV source, UV-LEDs that offer much more control for the radiation profile in the reaction system compared to traditional UV lamps, controlled hydrodynamics by implementing special flow channels to provide a more uniform residence time and offer enhanced mixing, and integrating UV reactor and electrochemical cell in a single unit which could lead to superior performance and space efficiency of the device. These features make the device very suitable for point-of-use (POU) water treatment applications to eliminate both microbial and chemical contaminants.

Keywords: 2,4-D; 2e-ORR; Advanced oxidation process; Drinking water treatment; Organic contaminant degradation; UV-LED.