Microbial diversity and functional analysis in wastewater and sludge of wastewater treatment plants

Background The efficiency of wastewater treatment plants (WWTPs) relies heavily on microbial communities. However, the microbial characteristics of different treatment units in the Qian’an WWTP (Hebei, China) remain unclear. This study investigates its microbial diversity and functions to provide a basis for process optimization. Methods Samples were collected in October 2024 from four representative units were selected: sludge (group A), sedimentation tank water (group C), aeration tank water (group E), and raw wastewater (group F). Bacterial and fungal communities were analyzed via Illumina NextSeq 2000 PE300 platform sequencing, with functional potentials predicted using PICRUSt2 and FUNGuild, respectively. Results Bacterial richness was highest in groups A, C, and E and lowest in group F, whereas fungal richness was highest in groups C and E and lowest in group F. The microbial community structures of groups C and E were highly similar in terms of richness and diversity patterns, but both differed markedly from groups A and F. At the phylum level, bacteria in group A were significantly enriched in Chloroflexi and Firmicutes, and fungi by Rozellomycota; bacteria in groups C, E and F were mainly Proteobacteria and Bacteroidetes. Fungal composition varied significantly, with Rozellomycota in A, Blastocladiomycota in C/E, and Ascomycota in F. Predicted Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed 25 differential metabolic pathways ( e.g ., amino acid and carbohydrate metabolism). Furthermore, 24 predicted functional genes related to nitrogen metabolism (nitrification, nitrogen fixation) were inferred, suggesting strong nitrogen cycling potential. Fungal functional groups differed significantly among groups: Ectomycorrhizal fungi dominated in group A, Insect Parasite-Undefined Saprotroph in groups C and E, and Animal Pathogen was predicted to account for up to 54.41 ± 4.75% in group F. Conclusions This study clarifies the microbial characteristics across treatment units and highlights the nitrogen cycling potential of the WWTP microbiome, providing a scientific basis for optimizing treatment processes.