A microwave-driven deep-UV ZnI2 light source for degrading organic wastewater: comparison with mercury lamp

The traditional cathode low-pressure Hg lamp is the most mainstream UV light source in degrading organic wastewater but with significant limitations of short lifetime, environmental hazard and poor degradation efficiency. Here, we evaluate a self-designed microwave-driven ZnI 2 deep-UV lamp on degrading Rhodamine B (RhB), methylene blue (MB), and p-nitrophenol (PNP). An electrodeless Hg lamp was used as control. First we investigated the emission wavelength, spatial radiation distribution, the effect of power on radiation intensity, and relative permittivity of ZnI 2 lamp. Then the degradation rate, kinetics and energy yield on degrading RhB, MB and PNP as well as the cost were studied. ZnI 2 lamp showed shorter wavelengths, approaching UVC radiation intensity, approaching attenuation factor and higher microwave coupling capability to Hg lamp. After treatment with ZnI 2 lamp for 10, 6 and 15 min, 5 mg/L of RhB, MB and PNP can reach 100% removal rates. Moreover, higher degradation rate and kinetic constants of ZnI 2 lamp for 3 compounds than the Hg lamp in this paper and in the literature were achieved. With the assistance of microwave and properties of environmental-friendly and low cost, ZnI 2 lamp provides a new alternative to traditional Hg lamp and wastewater photochemical treatment method.