Assessing the effectiveness of monochromatic (254 nm) versus polychromatic (200--600 nm) UV lamps in the inactivation of bacteria and viruses in water

The use of Ultraviolet Light as a disinfection method has become a viable alternative to chlorine for the treatment of water and wastewater. Currently, two types of UV lamps are used in the disinfection of water and wastewater; the monochromatic Low Pressure Low Intensity and the polychromatic Medium Pressure High Intensity UV lamps. To determine the germicidal effectiveness of the UV lamps in inactivating microorganisms, the LPLI and MPHI UV lamps were used in a collimated beam unit because the CBU is the only reliable method to measure UV dose. Phase I assessed the disinfection effectiveness of the MPHI and LPLI UV lamp on 5 different secondary wastewater treatment process effluent (attached growth and suspended growth) by determining the inactivation of fecal coliform, enterococci and Clostridium perfringens . Phase II compared the germicidal effectiveness of the MPHI and LPLI UV lamps on the inactivation of selected viruses (i.e., poliovirus, MS2, PRD-1, Phi-6, T4, Phi-X174) in water. Phase III determined whether the germicidal effectiveness of the MPHI UV lamp on viruses varied proportionately to the wavelength emitted at 254 nm when the input power to the lamp was decreased.;Results for Phase I showed that the effluent quality of the attached growth processes provided protection to the microorganism (i.e., formation of extracellular polymers) from UV radiation as compared to the suspended growth processes. Total Suspended Solids levels also had an impact on the particulate-associated portion of the dose response curve of all organisms tested. Lastly, the germicidal effectiveness of the MPHI was 3-4 times greater than the LPLI UV lamp, suggesting that wavelengths in addition to that produced at 254 nm are responsible for indicator bacteria inactivation.;Result of Phase II indicated that the germicidal effectiveness of the MPHI and the LPLI UV lamps on viruses are different and cannot be predicted based solely on the structural or genetic composition of the viruses.;Lastly, in Phase III, results indicated that the germicidal effectiveness of the MPHI UV lamp varied proportionately to the intensity measured at 254 nm when the power input to the MPHI UV lamp was lowered for all viruses tested, with the exception of PRD-1 and Phi-6.