A New In-Line GAC-Based Device for Concentrating Viruses in Treated Wastewater: Implications for Full-Scale UV C LED Treatment

UV C LEDs are an emerging technology offering wavelength-specific control for microbial inactivation in water and wastewater treatment. As these systems advance, complementary monitoring methods are needed to accurately evaluate the treatment performance and viral persistence in complex effluents. This study developed and evaluated an in-line granular activated carbon (GAC) sampling device designed to concentrate large volumes of wastewater from a full-scale UV C LED reactor. Compared to 1 L grab samples, GAC-concentrated samples recovered significantly higher nucleic acid concentrations (<i>p</i> < 0.001). Viral diversity was also more abundant in GAC-concentrated samples, with 85.7% abundance of <i>Adenoviridae</i> and multiple codetected viral families, whereas grabs had 95% <i>Adenoviridae</i> abundance with minimal diversity of other viral families. Likewise, grab samples were found to be more sensitive to matrix effects compared with the GAC-concentrated samples, with significant negative associations between nucleic acid yield and flow and UV transmittance. Collectively, these findings demonstrate that the in-line GAC approach can overcome the limitations of grab samples, providing a scalable, operationally compatible solution for real-time monitoring of viruses during wastewater treatment.