Estimating effective germicidal dose from medium pressure UV lamps

Three methods of estimating effective germicidal ultraviolet (UV) dose in a collimated beam medium pressure UV system were analyzed: (1) A bioassay; (2) a mathematical model; and (3) a chemical actinometer. The bioassay was performed with MS2 phage. The mathematical model was used to estimate incident, average, and effective germicidal intensity. The chemical actinometer used was uridine, which contains a uracil nucleobase with an absorbance spectrum similar to that of MS2 phage. The average and effective germicidal intensity, terms often equated in low pressure UV systems, differed by 27% for the medium pressure UV system used in this research. The effective germicidal dose determined mathematically was within 10% of the dose estimated with the bioassay approach. For the uridine actinometry, when the differences in the relative absorbance spectras of the uridine actinometer and MS2 phage were accounted for, the actinometry and bioassay methods resulted in similar estimations of effective germicidal dose.