Microbial and Viral Dynamics and Diversity in an Activated-Sludge Wastewater Treatment Plant

Wastewater Treatment Plants (WWTPs) are vital for reducing microbial contamination and protecting public health. A comprehensive understanding of microbial dynamics within these systems is crucial for optimizing treatment processes and effectively managing generated sludge. Abundances and dynamics of bacterial and viral fecal indicators throughout the treatment in an activated-sludge WWTP were assessed from mid-spring to late summer, combining viable counts and quantitative PCR. Wastewater and sludge microbiomes were characterized through 16S rRNA amplicon-sequencing, whereas the diversity of Human Adenoviruses (HAdVs) and Human Enteroviruses (EVs) was assessed using NGS. The abundance of viable and total enterococci decreased from influent to post-treatment samples, showing a seasonal pattern. A broad diversity of HAdVs serotypes (from species A, B, and F) was identified in the influent, whereas three serotypes dominated among EVs. Distinct core bacterial communities were identified in influent and belt-filtered dewatering sludges (BFDS) samples. Only eight genera (24 ASVs) were shared, accounting for a small fraction of total abundances (up to 6.6% and 14.0%, respectively). Arcobacter (1.6%-34.1%), Acinetobacter (4.7%-7.5%), and Trichococcus (12.9%-0.62%) dominated the influent core microbiome, showing a clear seasonal pattern. In contrast, Nitrospira (4.5%-10.7%) predominated in the BFDS core along with several uncharacterized taxa from MiDAS classifications. The influent microbiome was the most affected by seasonal changes, showing a decrease in diversity during summer. Overall, this study provides new insights into bacterial and viral indicator dynamics throughout the activated-sludge WWTP and into bacterial and viral diversity and composition inhabiting these critical ecosystems, highlighting the relevance of a multidisciplinary approach. • In contrast to sludge microbiomes, those from the influent were seasonally affected. • Viable and total enterococci showed seasonal patterns, decreasing along the WWTP. • A large diversity of HAdV and few relevant EVs were detected in the influent.