New water disinfection system using UVA light‐emitting diodes

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‐log 10 stages within 75 min at 315 J cm −2 of UVA. Salmonella enteritidis was reduced greater than 4‐log 10 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 (H 2 O 2 ) to bacterial suspensions significantly suppressed disinfection effect of UVA‐LED. Conclusion:  This disinfection system has enough ability to inactivate bacteria and OH ˙ and H 2 O 2 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.