Low-pressure microwave plasma ultraviolet lamp for water purification and ozone applications

Low-pressure mercury lamps are commonly used for germicidal applications. The germicidal effect is due to the emission of light at 254 nm, which leads to the destruction of the most waterborne bacteria and viruses. The microwave plasma ultraviolet (UV) lamp (MPUVL) is a new technology for generating a high-intensity UV light and that can be also controlled to operate at 185 nm; irradiation is in air at this wavelength produces ozone. The microwave power is injected into a resonant cavity and the surface wave excitation takes place within the cavity through that part of the discharge tube (fused silica) protruding inside it. The MPUVL has many advantages over conventional lamps, which are limited to an output power in the region of 30 W m(-1), while MPUVL can deliver any amount of power per unit length and the tube can be of any shape, length or diameter. This paper describes the design of the MPUVL and compares its efficiency with that of conventional lamps through spectral analysis. Other results, which include the effects of temperature and different power inputs, are also discussed.