Metagenomic  diversity of activated sludge
First, genomic DNA was extracted and purified. The DNA was then fragmented using a Covaris M220 system, followed by end-repair, A-tailing, and adapter ligation. The adapter-ligated fragments were amplified by PCR. Sequencing was performed on an Illumina Novaseq 6000 platform. Raw sequencing reads were qualityfiltered with fastq to remove reads with quality scores <20, lengths <50 bp after trimming, or containing ambiguous bases (N). Contigs 300 bp were retained for final assembly. Genes sharing 90% identity and 90% coverage were clustered with CDHIT to construct a nonredundant gene set. This gene set was aligned against the NR and KEGG databases for taxonomic and functional annotation.