title: activated sludge sample 3
design: The samples were sent to Majorbio (Shanghai, China) for analysis on an Illumina Miseq platform. The paired-end reads were overlapped using Flash followed by quality filtering conducted on Trimmomatic using the Sliding Window approach. UPARSE (version http://drive 5. com/uparse/) was used at an identity threshold of 0.97 to cluster sequences into different operational taxonomic units (OTUs), and UCHIME was conducted to identify and remove chimeric sequences. Chao1, Shannon index, and other indexes were determined by MOTHUR in accordance with the standard procedures (Ma et al., 2017). Each 16S rRNA gene sequence from OTUs was assigned to taxonomy with RDP Classifier (http://rdp. cme.msu.edu/) and unite pipeline respectively with a confidence threshold of 70%. Microbial diversity analysis was performed on the Majorbio Cloud Platform (www.majorbio.com).