This study used 454 pyrosequencing to analyze the bacterial diversity of activated sludge (AS) samples from 14 sewage treatment plants (STPs) in Asia and North America. A total of 259,000 effective 16S rRNA gene sequences were obtained, revealing a high number of operational taxonomic units (OTUs), ranging from 1,183 to 3,567 per sample. The results showed significant geographical differences among the AS samples, as demonstrated by cluster analysis and principal coordinate analysis (PCoA). The study identified several dominant bacterial genera, including Zoogloea and Dechloromonas, as well as several less commonly reported genera. Additionally, some genera were found to be unique to specific samples. The study also revealed a large proportion of sequences that could not be assigned to known taxonomic groups, highlighting the complexity of AS microbial communities. The findings suggest that while there are core bacterial populations shared among different AS samples, there are also unique populations that vary by location and treatment process. The study also compared the results with previous studies, showing that the bacterial communities in AS samples are highly diverse and complex, with Proteobacteria being the most abundant phylum. The study highlights the importance of using high-throughput sequencing techniques to better understand the microbial diversity in AS and its role in wastewater treatment. The results also indicate that factors such as sewage composition, temperature, and industrial wastewater contribution can significantly influence the microbial community structure in AS. The study concludes that further research is needed to fully understand the factors shaping microbial communities in AS and their roles in wastewater treatment processes.This study used 454 pyrosequencing to analyze the bacterial diversity of activated sludge (AS) samples from 14 sewage treatment plants (STPs) in Asia and North America. A total of 259,000 effective 16S rRNA gene sequences were obtained, revealing a high number of operational taxonomic units (OTUs), ranging from 1,183 to 3,567 per sample. The results showed significant geographical differences among the AS samples, as demonstrated by cluster analysis and principal coordinate analysis (PCoA). The study identified several dominant bacterial genera, including Zoogloea and Dechloromonas, as well as several less commonly reported genera. Additionally, some genera were found to be unique to specific samples. The study also revealed a large proportion of sequences that could not be assigned to known taxonomic groups, highlighting the complexity of AS microbial communities. The findings suggest that while there are core bacterial populations shared among different AS samples, there are also unique populations that vary by location and treatment process. The study also compared the results with previous studies, showing that the bacterial communities in AS samples are highly diverse and complex, with Proteobacteria being the most abundant phylum. The study highlights the importance of using high-throughput sequencing techniques to better understand the microbial diversity in AS and its role in wastewater treatment. The results also indicate that factors such as sewage composition, temperature, and industrial wastewater contribution can significantly influence the microbial community structure in AS. The study concludes that further research is needed to fully understand the factors shaping microbial communities in AS and their roles in wastewater treatment processes.