UV LED TECHNOLOGY FOR COMPREHENSIVE SURFACE DISINFECTION: ADDRESSING BIOFILM INACTIVATION, SPORE FORMATION, AND DIVERSE MATERIAL CHALLENGES

Abstract

The use of ultraviolet (UV) irradiation for inactivation of microorganisms is well established in water treatment. Through the emergence of UV light emitting diodes (LEDs), the replacement of mercury-based systems is now more feasible than ever. LEDs boast benefits such as flexible deployment, mercury-free chips, and wavelength selectivity. These characteristics open the door for new inactivation applications, such as irradiation of surfaces, an area not yet well defined across the literature.

This thesis investigates the use of germicidal 280 nm UV LEDs for the inactivation of A. brasiliensis, C. albicans, P. aeruginosa, B. subtilis, S. aereus held in liquid suspension, in biofilm and across materials typical of residential and commercial spaces (glass, plexiglass, stainless steel, PVC, PTFE, Epoxy, and Silicone). Materials were subject to fouling chemically (phenolic disinfectant) and physically (wheel scuffs). This study is the first to provide experimental data supporting these effects, establishing a baseline for predicting the behaviour of other pathogens and materials under UV-C and provides advancements for innovative use of UV LEDs for surface inactivation. Results showed that direct irradiation of surface-bound microbes impacts inactivation effectiveness when compared to typical, in-solution irradiation.

In-solution testing revealed variation in UV susceptibility across the species tested, with C. albicans demonstrating the greatest sensitivity, while the bacterial species P. aeruginosa, B. subtilis and S. aereus achieved similar inactivation potential. The most UV-resistant bacterial species were B. subtilis (k = 0.318 mJ/cm2) and A. brasiliensis (k = 0.0147 mJ/cm2) for the fungi at 280 nm, representing the broad spectrum of UV sensitivities across microbes and reinforcing the value of diversifying experimentation.

This thesis demonstrates that surface characteristics, such as roughness and reflectivity, are key factors that should be considered when assessing the feasibility of applying UV LED surface disinfection of surface-bound microbes and biofilms. Physically fouled surfaces achieved a statistically lower LRV compared to pristine surface inoculation alone. This suggests that mechanical fouling (e.g. wheel scuffs) may slightly modify surface topology, partially mitigating the shielding effects observed in surface inoculation alone. However, consistency between log reduction values and modelled k-values across materials indicates that UV LED disinfection remains effective despite physical surface fouling and provides the first demonstration that UV LED disinfection is an effective and viable option for physically fouled surfaces.