Microwave discharge electrodeless lamps (MDELs). Part IX. A novel MDEL photoreactor for the photolytic and chemical oxidation treatment of contaminated wastewaters

Abstract

This article reports on the fabrication and enhanced performance of a novel microwave discharge electrodeless lamp (MDEL) consisting of a three layered cylindrical structure that was effective in the remediation of wastewater containing the 2,4-D herbicide and the near total sterilization of bacteria-contaminated pond water (E. coli and other microorganisms) through photolysis with the emitted vacuum-UV (185 nm) and UVC (254 nm) light from the MDEL and through chemical oxidation with reactive oxygen species (ROS) produced by the photolysis of dioxygen and air oxygen through one of the photoreactors. The flow rates of the 1.0 L contaminated waters were 0.6 and 1.2 L min⁻¹. The integrated UV/ROS_O2 and UV/ROS_air methods used to carry out the degradation of 2,4-D and sterilization processes were more effective than either the UV method alone or the ROS_O2 and ROS_air methods for short time periods (5 or 8 min). At a lower flow rate, 79% of 2,4-D was degraded by the UV/ROS_O2 method and 55% by UV/ROS_air after 8 min. At a faster flow rate of 1.2 L min⁻¹, degradation of 2,4-D in 1.0 L volume of water was 84% and 77% complete by the UV/ROS_O2 and the UV/ROS_air method, respectively, after 8 min of irradiation. The number of kills of E. coli bacteria was nearly quantitative (98 and 99%) by the UV/ROS_O2 and UV/ROS_air methods after treating the contaminated water for 5 min. The decrease of total viable microorganisms in pond water was 90% and 80% after 5 min of microwave irradiation at a flow rate of 1.2 L min⁻¹ by the integrated methods UV/ROS_O2 and UV/ROS_air, respectively. The rate of flow of oxygen gas through the photoreactor impacted the extent of degradation and the related dynamics of the 2,4-D herbicide.