SPECTRAL SENSITIVITY OF TEST MICROORGANISMS FOR VALIDATION OF UV REACTORS IN WATER DISINFECTION

The microbicidal UV fluence under polychromatic radiation from UV lamps is typically measured using the DNA absorbance spectrum as weighting factor for the relative wavelength effectiveness. However, this DNA based weighting does not necessarily match the spectral sensitivity of the microorganism being tested. Bacillus subtilis spores and MS2 coliphage were exposed to quasi-monochromatic UV irradiation across the microbicidal spectrum at wavelengths of 214, 230, 240, 254, 265, 280 and 293 nm. MS2 was three times more sensitive to wavelengths near 214 nm compared to the 254 nm output of low pressure lamps, while B. subtilis spores were most sensitive to wavelengths around 265 nm. Use of these action spectra, compared to the DNA based weighting, resulted in differences in the calculated polychromatic UV fluence. Consequently, the action spectrum, which is specific for each microorganism, has implications on the uncertainty of UV fluence determination during validation of reactors with polychromatic UV lamps. Data in this paper were first published in Environ. Sci. Technol. (2005), 39, 7845-7852.