New water disinfection system using UVA light-emitting diodes

Abstract

Aim: To evaluate the ability of high‐energy ultraviolet A (UVA) light‐emitting diode (LED) to inactivate bacteria in water and investigate the inactivating mechanism of UVA irradiation. Methods and Results: We developed a new disinfection device equipped with high‐energy UVA‐LED. Inactivation of bacteria was determined by colony‐forming assay. Vibrio parahaemolyticus, enteropathogenic Escherichia coli, Staphylococcus aureus and Escherichia coli DH5α were reduced by greater than 5‐log₁₀ stages within 75 min at 315 J cm⁻² of UVA. Salmonella enteritidis was reduced greater than 4‐log₁₀ stages within 160 min at 672 J cm⁻² of UVA. The formation of 8‐hydroxy‐2′‐deoxyguanosine in UVA‐LED irradiated bacteria was 2·6‐fold higher than that of UVC‐irradiated bacteria at the same inactivation level. Addition of mannitol, a scavenger of hydroxyl radicals (OH^˙), or catalase, an enzyme scavenging hydrogen peroxide (H₂O₂) to bacterial suspensions significantly suppressed disinfection effect of UVA‐LED. Conclusion: This disinfection system has enough ability to inactivate bacteria and OH^˙ and H₂O₂ participates in the disinfection mechanism of UVA irradiation. Significance and Impact of the Study: We newly developed UVA irradiation system and found that UVA alone was able to disinfect the water efficiently. This will become a useful disinfection system.