Microbial community characterization in advanced water reclamation for potable reuse

Abstract: This study investigated the microbial community structure and composition across two treatment steps used in advanced water reclamation for potable reuse applications, namely Coagulation/Flocculation/Clarification/Granular Media Filtration (CFCGMF) and Ozone-Biological Activated Carbon filtration (O₃/BAC). The study examined the richness, variations, and similarities of the microorganisms involved at each treatment step to better understand the role of ecology and the dynamics on unit process performance and the microbial community developed within it. The bacterial microbiomes at each treatment step were independently characterized using 16S metagenomic sequencing. Combining both treatment steps, a total of 3801 species were detected. From the total species detected, 38% and 98% were identified at CFCGMF and O₃/BAC, respectively. The most abundant phyla were Proteobacteria, Bacteroidetes, Actinobacteria, and Firmicutes in both treatment steps. The identified species were classified based on their preferences to free-living style (59%) vs attached-living style (22%) showing a relatively low richness in the BAC media, but higher diversities. At the taxonomic class level, Betaproteobacteria was the predominant in both system processes. Additionally, a list of eight genera were identified as potential bacterial pathogens present in both process effluents. They are Aeromonas, Clostridium, Enterobacter, Escherichia, Flavobacterium, Legionella, Mycobacterium, and Pseudomonas. CFCGMF effluent yielded less pathogenic bacteria than both the ozone and BAC filter effluent from the O₃/BAC process unit; their relative abundance accounted for about 2% and 8% for CFCGMF and O₃/BAC, respectively. Detailed studies to characterize the microbial communities are crucial in interpreting the mechanisms and synergies between processes performance and microorganisms by identifying the needs and best practices to ensure public health protection. Key points • Microbial communities of two treatment processes are characterized using 16S rRNA sequencing. • Organisms that can tolerate ozone and form biofilms define microbial community in subsequent biofilters. • In relatively low abundances, potential pathogenic bacteria are detected in the treated water.