Inactivation of biofilm-bound bacterial cells using irradiation across UVC wavelengths

Ben Ma; Saba Seyedi; Emma Wells; David McCarthy; Nicholas Crosbie; Karl G Linden

doi:10.1016/j.watres.2022.118379

Inactivation of biofilm-bound bacterial cells using irradiation across UVC wavelengths

Water Res. 2022 Jun 15:217:118379. doi: 10.1016/j.watres.2022.118379. Epub 2022 Mar 31.

Authors

Ben Ma¹, Saba Seyedi¹, Emma Wells¹, David McCarthy², Nicholas Crosbie³, Karl G Linden⁴

Affiliations

¹ Department of Civil, Environmental, and Architectural Engineering, University of Colorado Boulder, 4001 Discovery Dr., Boulder, CO, 80303, United States.
² Department of Civil Engineering, Monash University, Clayton, Vic, 3800, Australia.
³ Melbourne Water, Docklands Vic 3008, Australia.
⁴ Department of Civil, Environmental, and Architectural Engineering, University of Colorado Boulder, 4001 Discovery Dr., Boulder, CO, 80303, United States. Electronic address: karl.linden@colorado.edu.

PMID: 35429876
DOI: 10.1016/j.watres.2022.118379

Abstract

Opportunistic pathogens (OPs), such as Pseudomonas spp., Legionella spp., and mycobacteria, have been detected in biofilms in drinking water distribution systems and water storage tanks and pose potential risks to finished drinking water quality and safety. Emerging UV technologies, such as UV light emitting diodes (LEDs) and krypton chloride (KrCl*) excimers, could provide an alternative to chemical-based secondary disinfection (i.e., chlorine or chloramines) for controlling biofilm-bound OPs. UV systems offer long lifetimes, ability to select wavelength, small size with high power density, and limited-to-no disinfection by-product formation. In this study, inactivation of biofilm-bound Pseudomonas aeruginosa cells across different maturities was investigated using five UVC devices with different peak emission wavelengths, including a KrCl* excimer (222 nm), a low pressure mercury vapor lamp (254 nm), and three UV LEDs (260 nm, 270 nm, and 282 nm). The UV transmittance and absorbance through the biofilm structure was also documented for the first time using a unique approach. Our results show all UVC devices can inactivate biofilm-bound P. aeruginosa cells up to a point, among which the UV LED with peak emission at 270 nm provided the best disinfection performance. UV sensitivities of biofilm-bound cells decreased with biofilm maturity and while initial rates of inactivation were high, no more than 1.5-2.5 log reduction was possible. Re-suspended biofilm bacteria in aqueous solution were highly sensitive to UV, reaching greater than 6 log reduction. UV shielding by biofilm constituents was observed and was likely one of the reasons for UV resistance but did not fully explain the difference in UV sensitivity between biofilm-bound cells versus planktonic cells. This study improves upon fundamental knowledge and provides guidance for innovative designs using emerging UV technologies for biofilm and pathogen control in water distribution systems.

Keywords: Krypton chloride excimer; LED; Pseudomonas aeruginosa; UV disinfection; UV light emitting diodes; Water distribution system.

MeSH terms

Biofilms
Chlorine
Disinfection / methods
Drinking Water*
Ultraviolet Rays
Water Purification* / methods

Substances

Drinking Water
Chlorine