Microwave discharge electrodeless lamps (MDEL) Part IV. Novel self-ignition system incorporating metallic microwave condensing cones to activate MDELs in photochemical reactions

Abstract

A metallic condensing cone that concentrates microwave radiation (equivalent to an optical lens) has been developed and used as part of a system to activate a microwave discharge electrodeless lamp (MDEL) in the oxidative treatment of wastewaters by aiding the novel self-ignition of the lamp on irradiation at low microwave power levels. This approach to self-ignition can potentially lead to considerable energy savings in such treatments. System performance was examined for the ignition power of microwaves of such MDEL devices in water, whose usefulness was assessed by investigating the photolytic transformation of aqueous solutions of representatives of three classes of contaminants: chlorinated phenols, herbicides and endocrine disruptors, specifically 4-chlorophenol (4-CP), 2,4-dichlorophenoxyacetic acid (2,4-D) and 4,4'-isopropylidenediphenol (bisphenol-A; BPA), respectively, taken as model wastewaters in air-equilibrated, in oxygen-saturated and in TiO2-containing aqueous media. The results are discussed in terms of the dynamics of the photo-induced degradation processes.

Photoreactors for Wastewater Treatment: A Review

“…Gamma-rays 0.00001-0.001 - 60 Co gamma source [5][6][7][8] -sewage-sludge: solubilization, neutralization and improved filterability [4,9], -wastewater treatment: elimination of bacterial flora; BOD, COD, ammonia nitrogen, toxicity and TSS decrease [4,5,8,10,11]; biodegradability increase (BOD/COD) [6,12]; degradation of thebaine [13]; dechlorination of PCE [7] X-rays 0.001 -10 -Cu K , Synchrotron radiation [14], XeL [17], KrCl * L [16], TUV [22], ML [23], LMPL [24], W-MDEL [20] UV: germicidal [11,16,24]; UV/H2O2: germicidal [24], decolorization of river water [25], decomposition of: phenol [26], DMDT [27], real pesticide wastewater [28]; UV/O3: phenol degradation [23],…”

Microwaves in Photochemistry and Photocatalysis

“…Horikoshi and co-workers [32,119] also developed a metallic condensing cone that concentrates MW radiation (equivalent to an optical lens) into an MW-UV photoreactor and used it as a part of the system to activate a quartz Hg-EDL (185 and 254 nm) in the oxidative treatment of wastewater. This approach to self-ignition of an EDL immersed in solution led to considerable energy savings.…”

“…An EDL immersed in aqueous solution presents some problems with regard to the continuity of UV/Vis light and most importantly self-ignition of a lamp by MW radiation [120]. This arises because when the EDL is used in aqueous media having a high dielectric loss factor, most of the MWs are absorbed by the dielectric medium.…”

“…The second method involves the use of a tungsten trigger connected to the EDL [118] and the third technique includes a newly designed metallic condensing cone (equivalent to an optical lens) connected to a waveguide, which concentrates the MW radiation on to the sample [119]. The fourth method involves the use of a novel microwave discharge granulated electrodeless lamp (MDGEL, 5 × 10 mm) [120], and demonstrates some advantages of miniaturization, that is, greater surface area for irradiation, at low MW power levels. This system has been evaluated through the photoassisted defluorination of perfluoroalkanoic acids [120].…”

“…The fourth method involves the use of a novel microwave discharge granulated electrodeless lamp (MDGEL, 5 × 10 mm) [120], and demonstrates some advantages of miniaturization, that is, greater surface area for irradiation, at low MW power levels. This system has been evaluated through the photoassisted defluorination of perfluoroalkanoic acids [120].…”