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.

Keywords: Bacillus pumilus spores; Combined wavelengths; Electrical energy per order; Human adenovirus type 2; Nucleic acid damage.

Fig. 1.

Emission spectra from (top) the 260 nm and 280 nm LEDs when illuminated separately, (middle) the unit with 260 nm and 280 nm LEDs illuminated together (260|280 nm) and (bottom) a medium-pressure (solid) and low-pressure (dashed) mercury vapor lamp

Fig. 2.

UV dose response of a) E. coli, b) MS2 coliphage, c) HAdV2 as measured by ICC-qPCR, d) HAdV2 as measured by cell culture, and e) B. pumilus spores to LP irradiation from UV LEDs emitting at 260 nm, 280 nm and 260|280 nm combined. Results are shown in comparison to MP UV and LP UV irradiation, when available. Error bars represent ± 1 standard deviation. The up-down in Fig. 2d illustrates that the assay detection limit was reached.

Fig. 3.

Electrical energy per order (E_EO) of reduction of E. coli and MS2 coliphage and electrical energy per 2-log reduction(E_EL,2) for HAdV2 and B. pumilus for the five UV sources. Error bars represent ± 1 standard deviation. Note the different y-axis values.

Fig. 4.

UV dose response of a 260|280 nm combined LED unit (solid line) compared with sum of its UV dose response from separate LED exposures on inactivating a) E. coli, b) MS2 coliphage, c) HAdV2 as measured by cell culture and ICC-qPCR (inset), and d) B. pumilus spores.

Fig. 5.

Log reduction in amplification of a) HAdV2 DNA and b) MS2 coliphage RNA to UV light from a UV LED unit emitting at 260 nm, 280 nm and 260|280 nm.