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

Abstract

Mercury lamps are typically the major light sources in water treatments. However, the use of mercury has raised some concerns with regard to the Minamata Convention on Mercury. As such, Hg-free microwave discharged electrodeless lamps (MDELs) that incorporate a rare gas and a halogen gas (R/H-MDEL) have been investigated with such Hg-free mixture filler gases as Kr/Cl 2 , Xe/Cl 2 , and Kr/Br 2 (R/H). Of these, only the Kr/Br 2 -MDEL lamp is self-ignited at an inner pressure of 15 Torr when irradiated with microwave radiation. Accordingly, a novel Kr/Br 2 three-layer MDEL (Kr/Br 2 -MDEL) photoreactor was fabricated to assess the optimal gas composition and gas pressure toward its performance vis-à-vis the treatment of model wastewaters contaminated with the tartrazine dye in aqueous media and with Escherichia coli (E. coli) bacteria. The extent of degradation of the tartrazine dye and sterilization of E. coli increased with irradiation time, with microwave radiation power (100, 200, and 300 W), and with increased sample flow rate 0.4 L min -1 to 0.8 L min -1 . The tartrazine-contaminated wastewater was treated at a flow rate of 0.4 L min -1 for 60 min of microwave irradiation by three different protocols that resulted in UV (62%) >> UV/ROS (24%) > ROS (0%); ROS denotes reactive oxygen species. After 5 min irradiation of the E.coli wastewater, also at 0.4 L min -1 , the order was UV (99.5%) ≈ UV/ROS (99.3%) >> ROS (14.5%). For comparison, the photosterilization of E. coli with an equivalent Hg/Ar-MDEL light source was also nearly complete (99.7%). Thus, the suitability of the environmentally friendlier Kr/Br 2 gas fill to replace Hg/Ar filler gas in MDELs for the photoelimination of organic pollutants and microbial disinfection in aqueous media has been demonstrated.

Development of a microwave-discharge light-emitting diode (MDLED): a novel UV source for the UV-driven microwave-assisted TiO2 photocatalytic treatment of contaminated wastewaters

“…Accordingly, current commercially available mercury-based UV lamps are now subjected to the enacted mercury regulations. As a result, our later study [13] developed MDEL lamps filled with Kr/Br 2 as the new filler gases that when exposed to microwaves emitted UVC light at 207 nm, 222-228 nm, and 291 nm.…”