Evaluating UV-C LED disinfection performance and investigating potential dual-wavelength synergy

Abstract

A dual-wavelength UV-C LED unit, emitting at peaks of 260 nm, 280 nm, and the combination of 260|280 nm together was evaluated for its inactivation efficacy and energy efficiency at disinfecting Escherichia coli, MS2 coliphage, human adenovirus type 2 (HAdV2), and Bacillus pumilus spores, compared to conventional low-pressure and medium-pressure UV mercury vapor lamps. The dual-wavelength unit was also used to measure potential synergistic effects of multiple wavelengths on bacterial and viral inactivation and DNA and RNA damage. All five UV sources demonstrated similar inactivation of E. coli. For MS2, the 260 nm LED was most effective. For HAdV2 and B. pumilus, the MP UV lamp was most effective. When measuring electrical energy per order of reduction, the LP UV lamp was most efficient for inactivating E. coli and MS2; the LP UV and MP UV mercury lamps were equally efficient for HAdV2 and B. pumilus spores. Among the UV-C LEDs, there was no statistical difference in electrical efficiency for inactivating MS2, HAdV2, and B. pumilus spores. The 260 nm and 260|280 nm LEDs had a statistical energy advantage for E. coli inactivation. For UV-C LEDs to match the electrical efficiency per order of log reduction of conventional LP UV sources, they must reach efficiencies of 25-39% or be improved on by smart reactor design. No dual wavelength synergies were detected for bacterial and viral inactivation nor for DNA and RNA damage.

UV-LEDs Efficiently Inactivate DNA and RNA Coliphages

“…In earlier UV-LED studies more than 3 Log 10 -reductions of coliphages φX174 and T7 were achieved with doses of 6.4-20 mWs/cm 2 at wavelengths of 255-285 nm [18,24]. Coliphages Qβ and MS2 were more resistant and they required above 40 mWs/cm 2 to reach 1-3 Log 10 -reductions [13,16,18,21,23,24]. Bowker et al [18] compared the wavelengths of 255 and 275 nm with coliphages T7 and MS2 and found rather similar inactivation rates at both wavelengths.…”

“…Compared to a single wavelength, simultaneous treatment with multiple wavelengths of UV-C and UV-A have yielded higher reductions of fecal enterococci and total and fecal coliforms in wastewater and in pure cultures [40,41] and Vibrio parahaemolyticus in pure culture [42]. On the other hand, the UV-LEDs at wavelengths 260 nm and 280 nm irradiated separately or simultaneously yielded statistically similar reductions in E. coli, Bacillus pumilus spores, MS2, or adenovirus when the UV-doses were the same [13]. More studies are obviously needed on the effect of different wavelength combinations on viruses and other resistant microorganisms.…”

“…Bowker et al [18] compared the wavelengths of 255 and 275 nm with coliphages T7 and MS2 and found rather similar inactivation rates at both wavelengths. Qβ and MS2 were studied by [13,14,16] at wavelengths of 260, 275, and 280 nm and a wavelength of 260 was found to be more effective compared with the other wavelengths. Aoyagi et al [24] compared the wavelengths of 255 nm and 280 nm with different coliphages (φX174, Qβ, and MS2) and concluded that, even though the inactivation efficiency of 280 nm was lower than that of 255 nm, 280 nm LEDs are more suitable for practical applications due to their easier production at high-power output.…”

“…MS2 has also proved to be UV-resistant in other studies. Doses from 41 to 60 mWs/cm 2 were needed to reach 2-3 Log 10 -reductions of MS2 at wavelengths of 255-280 nm (excluding 270 nm) [13,18,24], while approximately 110 mWs/cm 2 was needed at 285 nm to reach 3 Log 10 -reduction [21]. However, a tunable laser at 270 nm has yielded 1.5 and at least 3 Log 10 -reductions of MS2 with doses of 20-30 mWs/cm 2 and 60 mWs/cm 2 , respectively [33,34].…”

“…MS2 and other UV-resistant coliphages tested by [13,16,18,21,24] were RNA viruses. In our study, however, either RNA or DNA coliphages could be UV-resistant or UV-sensitive.…”