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/ROSO2 and UV/ROSair 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 ROSO2 and ROSair methods for short time periods (5 or 8 min). At a lower flow rate, 79% of 2,4-D was degraded by the UV/ROSO2 method and 55% by UV/ROSair 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/ROSO2 and the UV/ROSair method, respectively, after 8 min of irradiation. The number of kills of E. coli bacteria was nearly quantitative (98 and 99%) by the UV/ROSO2 and UV/ROSair 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/ROSO2 and UV/ROSair, 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.

Microwave Discharge Electrodeless Lamps (MDELs). Part XI. Photolytic, Chemical Oxidation, and Photocatalytic Treatment of Aqueous Urea Solution with a Novel MDEL Photoreactor

“…Photolysis is carried out using the released vacuum ultraviolet light 185 nm , and chemical oxidation is carried out with the ROS generated by the photodecomposition of dioxygen and air oxygen in one of the photoreactors. We reported that this new MDEL is effective for the disinfection E. coli of water and the decomposition of 2,4-dichlorophenoxyacetic acid 2,4-D in water 16 . We have also reported that photocatalytic TiO 2 oxidation reaction significantly improved when the photocatalyst is simultaneously irradiated by microwaves and UV light 17 because electron transfer inside the TiO 2 photocatalyst is optically optimized by microwaves 18 .…”

Development of a Hg-free UV light source incorporating a Kr/Br2 gas, and its application for wastewater treatments

“…Protocols typically used in such treatments involved mercury-type electrode lamps that were subsequently replaced by electrodeless discharge lamps (EDLs) as the light sources, which when placed inside a microwave field effectively produced UV-Vis radiation; they are referred to as MDELs. Such microwave discharge electrodeless light sources use simultaneously both UV and microwave radiations to degrade effectively organic compounds and destroy microorganisms often found in contaminated waters [6].…”

“…Our research efforts reported previously have focused on novel MDELs that use advanced oxidation processes (AOPs) toward water treatment and air purification [6,8,9]. In some cases, these MDELs contained traces of mercury that posed some concerns to the environment with regard to Hg-toxicity exposure in the form of organic and inorganic mercury.…”

A new structure of microwave‐driven UV lamp

“…Research on the removal of the antibiotic ciprofloxacin from water by microwave UV lamps was also conducted 17 . Besides, Horikoshi et al developed a novel microwave electrodeless UV lamp for the photolysis and chemical oxidation of contaminated wastewater 18 . However, the intensity of light varies with the distance to microwave source, and the intensity of ultraviolet radiation increases as shortening the distance.…”