Overlooked intensity-effect relationship beyond dose-effect relationship in bacteria disinfection by 254 nm ultraviolet light

Abstract

Ultraviolet (UV) disinfection is widely used in water purification due to its high efficiency and safety. This study investigated the effect of varies UV intensity on bacterial disinfection at 254 nm. At a constant UV dose of 10 mJ/cm², the inactivation rate of Escherichia coli increases significantly from 0.5-log at 0.5 mW/cm² to 7.2-log at 10 mW/cm² with increasing UV intensity. Fitting the disinfection data to the Chick-Watson model, expressed as Inactivation rate= (k'/ln10)×Iⁿ×t= (k'/ln10)×I^n-1×D, revealed that the exponent n, representing the weighting effect of UV intensity, was consistently greater than 1. This finding indicates that increasing UV intensity is more effective for bacterial inactivation than simply extending exposure time. Photoreactivation experiments demonstrated that higher UV intensities led to reduced regrowth, with almost complete suppression observed at 10 mW/cm². Fluorescent staining, scanning electron microscopy, and selective culture experiments demonstrated that high-intensity UV accelerated membrane damage, resulting in increased numbers of both lethally and sublethally damaged cells. Prokaryotic transcriptome analysis revealed significant downregulation of repair-related pathways and upregulation of pathways associated with programmed cell death. Electron paramagnetic resonance analysis confirmed that elevated singlet oxygen levels contributed to cellular damage, complementing the direct effects of UV irradiation. These findings indicate that increasing UV intensity enhances bacterial inactivation not only by intensifying physical damage but also by disrupting repair mechanisms and inducing oxidative stress, thereby improving disinfection efficiency, which enhances the effectiveness of UV-based bacterial disinfection processes.

Graphical abstract

Keywords

UV disinfection / Light intensity / Membrane damage / DNA damage / Singlet oxygen

Highlight

	● High-intensity UV promoted inactivation rates and inhibited photoreactivation.
	● UV intensity both affects the UV dose and the apparent inactivation rate constant.
	● High-intensity UV generated ROS to damage membrane and downregulate repair genes.
	● Increasing light intensity is more effective than prolonging disinfection time.

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