Effective management of pre-existing biofilms using UV-LED through inactivation, disintegration and peeling

Abstract

Managing undesirable biofilms is constantly a hard problem in water treatment and distribution systems. Although ultraviolet-light emitting diode (UV-LED) irradiation, an emerging disinfection method with the chemical-free and emission-adjustable merits, has been widely reported effective to inactivate planktonic bacteria, there are few studies about UV-LED on biofilms. This study thereby attempts to merge this gap by exploring the performance and mechanism of UV-LEDs on the prefabricated Escherichia coli (E. coli) biofilms with varying irradiation conditions. Consequently, the wavelength of 275 nm exhibited better inactivation effect on the biofilm-bound bacteria than 268, 312 and 370 nm, achieving 3.2 log inactivation at fluence of 346.5 mJ/cm² and irradiance of 660 μW/cm². Further, irradiance and irradiation time were proposed for the first time a pair of conjugate variables correlating to log inactivation, as a modification of Bunsen-Roscoe reciprocity law. Moreover, the effect of UV irradiation on extracellular polymeric substances (EPS) in terms of the structure and chemical properties was investigated, which supports that the oxidative degradation of the polysaccharides and proteins in EPS matrix should be the primary reason for destroying the biofilm framework. Subsequently, an additional hydraulic shear was implemented on the irradiated biofilms, suggesting an effective way for enhanced biofilm removal.

Environmental Implication

Unwanted but ubiquitous biofilms in water and wastewater systems are highly hazardous events, leading to problems like microbial contamination, biocorrosion and particularly pathogens habitation. Ultraviolet (UV) irradiation is a non-chemical alternative of the conventional disinfection technique chlorination. While so far, most UV disinfection studies focused on planktonic bacteria but not biofilms. Besides, the conventional UV light source mercury lamp has evolved to UV-light emitting diode (UV-LED). This study will bridge the gap of the new technology (UV-LED irradiation) and the old problem (biofilm control), and then provide new insights and useful reference for effective management of biofilms in water environment.