| There has been increased interest in exploring the use of polychromatic ultraviolet (UV) light from medium pressure (MP) and pulsed-UV (P-UV) lamps as a disinfectant for water supplies in recent years. Traditional methods of UV fluence measurement, which were developed for monochromatic light sources, lack fundamental accuracy in estimating the germicidal UV fluence from polychromatic light sources.; In this study, a new approach for effective germicidal UV fluence quantification from polychromatic UV systems, using chemical actinometry, was developed. Based on the knowledge of specific lamp parameters and the water absorbance, a mathematical model combining direct chemical actinometry measurement and mathematical analysis was developed. Incident UV fluence, average UV fluence within the water body and the germicidally effective UV fluence were predicted from the model and compared with a radiometry-based mathematical model and biodosimetry (B. subtilis microbial challenge) to evaluate the accuracy of the model. Experiments were conducted on both the bench-scale collimated beam and the UV reactor scale. Results showed chemical actinometry coupled with mathematical analysis improved the accuracy of effective germicidal fluence measurement when using the biodosimetry results as a benchmark. Uridine and potassium iodide/iodate actinometers were used in the experiments.; A spherical actinometer, consisting of a quartz vessel containing a chemical actinometer, was used to obtain the fluence rate at certain coordinates in the LP and MP reactors in air or water media. This approach was shown to be a convenient tool for experimental determination of the fluence rate distribution in a UV reactor. The reflection and shadowing effects from adjacent lamps were demonstrated and quantified experimentally by using the spherical actinometer.; Quantum yields of KI/KIO3 and uridine actinometers in the 200–300nm range were determined by three different monochromatic light-providing instruments. At pH 9, the quantum yield of the 0.6 M KI/0.1 M KIO3 at 254 nm was 0.71 mole einstein−1. Quantum yield appeared to be constant below wavelength of 254 nm and decreased with increasing wavelength. At light intensity about 1mW cm−2, neutral pH, and low uridine concentration (μM range), the quantum yield of uridine at 254 Mn was 0.015 mole einstein−1. The quantum yield of uridine was determined to be independent of wavelength. |
