UV LED disinfection efficacy and the impacts on micropollutants during wastewater recycling processes

Ultraviolet Light Emitting Diodes (UV LEDs) are an emerging, innovative technology for final-stage water purification and disinfection, yet their application in wastewater recycling at pilot scale remains largely unexplored. The present study evaluated UV LED systems during pilot testing at a municipal wastewater treatment plant (WWTP), demonstrating effective disinfection of about 2-3 log inactivation. UV irradiation caused photolysis of four tested pharmaceuticals (naproxen, diclofenac, sulfamethoxazole, and ciprofloxacin) with 16-60% degradation observed. Conversely, acetaminophen (ACE) concentrations increased 2-3-fold following UV irradiation, a finding confirmed in follow-up laboratory experiments of UV-induced degradation of conjugated metabolites, known to be excreted in human urine. This highlights the need to improve conventional environmental risk assessments to account for the release of micropollutants from their conjugates, which may substantially increase risks to the aquatic environment. The study further demonstrates that water matrix composition - particularly the presence of organic matter - substantially influences UV-induced photochemical reactions. Overall, UV LEDs show strong potential as an efficient disinfection technology for treated wastewater reuse, though further research is needed to evaluate their performance against diverse microorganisms, micropollutants, and their metabolites in highly complex wastewater matrices.