A full-scale Co-located comparison of virus removal by membrane bioreactor and conventional activated sludge systems

Although removal of human enteric viruses is essential for safe water reuse, evidence-particularly for structurally intact viruses-remains limited. This study evaluated (i) the performance of full-scale conventional activated sludge (CAS) and membrane bioreactor (MBR) in removing intact viruses, and (ii) the suitability of a viral indicator for monitoring enteric virus reduction. Both systems were operated receiving raw wastewater from same area in Japan. Samples were collected from five points: influent, after primary sedimentation, CAS effluent, after chlorination, and MBR effluent. Viruses were concentrated by a two-step electronegative membrane and quantified by conventional-(RT-)qPCR and capsid-integrity-(RT-)qPCR employing sodium deoxycholate-cis-dichlorodiammineplatinum (SD-CDDP) for ten targets viruses. The use of both quantification approaches enabled differentiation between total viral genomes and potentially infectious viruses, thereby improving the assessment of treatment performance. PMMoV, CGMMV, and CrAssphage were consistently detected at high levels throughout all stages. MBR showed significantly higher removal of these viruses compared to CAS, while sedimentation and chlorination demonstrated lower reductions. Capsid-integrity-(RT-)qPCR consistently reported higher removal values than conventional-(RT-)qPCR, suggesting its effectiveness in detecting potentially infectious viruses. PMMoV consistently exhibited the highest detection frequency and concentration. Its persistence through both CAS and MBR, along with significant reductions and strong correlation with other enteric viruses, supports its suitability as a viral indicator for assessing virus concentration and removal efficiency in wastewater treatment. Overall, MBR demonstrated superior virus removal performance compared to CAS. These findings highlight the utility of capsid-integrity-(RT-)qPCR and PMMoV for monitoring virus reduction and ensuring microbial safety in wastewater reuse.