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 b ioassay; (2) a mathematical model; and (3) a chemical actinometer. The bioassay was performed with MS2 phage. The mathematical model was use d to estimate incident, average, and effective germicidal intensity. T he chemical actinometer used was uridine, which contains a uracil nucl eobase with an absorbance spectrum similar to that of MS2 phage. The a verage 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 mathe matically was within 10% of the dose estimated with the bioassay appro ach. For the uridine actinometry, when the differences in the relative absorbance spectras of the uridine actinometer and MS2 phage were acc ounted for, the actinometry and bioassay methods resulted in similar e stimations of effective germicidal dose.