Abstract
Pulsed UV (PUV) technology is accepted commercially for disinfection within the food packaging industry, but has yet to be deployed by the water/wastewater sector. This is partly due to a lack of robust, independently validated data for submerged or flow-through treatment applications. This study evaluated the efficacy of PUV for water disinfection under flow-through conditions. Bacterial pathogens of interest in the food and water/wastewater sector, namely Escherichia coli, Staphylococcus aureus and Listeria innocua (surrogate for L. monocytogenes) were used to investigate the potential for photoreactivation and/or dark repair post PUV flow-through disinfection. A continuous-flow low-pressure UV was also analysed under similar experimental conditions. Bacterial inactivation via flow-through PUV was dependant on energy output with E. coli exhibiting greatest sensitivity to PUV treatment (5.3 log 10 inactivation after treatment at 1539 mJ/cm 2 - output in UV range < 300 nm); L. innocua exhibited the highest PUV resistance (3.0 log 10 inactivation after treatment at 1539 mJ/cm 2 – output in UV range < 300 nm) under similar treatment conditions. Greater photoreactivation occurred at lower PUV outputs for both S. aureus and E. coli after flow-through PUV treatment. Thus exposure of treated bacteria to natural light, immediately post flow-through PUV treatment, should be avoided to minimise photoreactivation. The LPUV demonstrated inactivation of all bacteria below the limit of detection (1 CFU/mL) and inhibited the occurrence of photoreactivation. This study highlights the importance of considering bacterial repair potential and the need for further development of PUV technology for such applications.
Highlights
Ultraviolet (UV) disinfection is a well-established technology across a variety of different sectors including aquaculture, ballast water treat ment, municipal wastewater treatment, drinking water treatment, agriculture, dairy and the beverage industry [1,2,3]
Results in this study are in line with findings in the liter ature which illustrate vegetative cells are readily inactivated by Low pressure UV (LPUV) disinfection at relatively low UV energies
It is possible that low UV outputs puts less biocidal stress on the treated bacterial cells with potentially greater ability to repair as less physical, genomic and metabolic damage – lower doses may not cause irreversible damage. This constitutes the first study to demonstrate that bacterial (S. aureus and E. coli) photoreactivation is possible post flow-through Pulsed UV (PUV) disinfection and that the level of bacterial photoreactivation is depen dent upon the output energy applied during prior UV disinfection treatment
Summary
Ultraviolet (UV) disinfection is a well-established technology across a variety of different sectors including aquaculture, ballast water treat ment, municipal wastewater treatment, drinking water treatment, agriculture, dairy and the beverage industry [1,2,3]. UV light is generated within the lamps when a voltage is applied across a mercury gas mixture which results in the discharge of photons. The type of UV light produced is dependent upon the mercury vapour pressure; LPUV lamps produce monochromatic light at 253.7 nm under low vapour pressure while MPUV lamps produce a polychromatic light due to higher vapour pressures [6]. Pulsed UV (PUV) disinfection is a relatively new UV technology which differs to mercury vapour-based LPUV/MPUV light by utilising xenon gas to generate a high energy electron pulse, which typically lasts microsec onds. PUV systems generally comprise three parts; the power supply, the pulse configuration system and the flash lamp [7]. The high peak power stored in the capacitor is a trademark of this system, which has been shown in some cases to offer shorter treatment times [9,10].
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