This study investigates the bacterial diversity of activated sludge (AS) from 14 sewage treatment plants (STPs) in Asia and North America using PCR-based 454 pyrosequencing. A total of 259 K effective sequences of the 16S rRNA gene V4 region were obtained, revealing a high number of operational taxonomic units (OTUs) in each sample. Geographical differences were evident, with clear clustering based on OTU abundances, RDP taxa, and UniFrac distances. The study identified dominant genera such as Zoogloea and Dechloromonas, as well as less common genera like Prosthecobacter, Caldilinea, and Tricoccus. The results also highlighted unique populations in certain samples, possibly due to factors like salinity, temperature, and industrial wastewater. The study provides insights into the complex microbial communities in AS and suggests that high-throughput sequencing is a valuable tool for exploring these communities.This study investigates the bacterial diversity of activated sludge (AS) from 14 sewage treatment plants (STPs) in Asia and North America using PCR-based 454 pyrosequencing. A total of 259 K effective sequences of the 16S rRNA gene V4 region were obtained, revealing a high number of operational taxonomic units (OTUs) in each sample. Geographical differences were evident, with clear clustering based on OTU abundances, RDP taxa, and UniFrac distances. The study identified dominant genera such as Zoogloea and Dechloromonas, as well as less common genera like Prosthecobacter, Caldilinea, and Tricoccus. The results also highlighted unique populations in certain samples, possibly due to factors like salinity, temperature, and industrial wastewater. The study provides insights into the complex microbial communities in AS and suggests that high-throughput sequencing is a valuable tool for exploring these communities.