Are adding carbon sources and activated sludge helpful to the full-scale packing-reinforced multistage biological...

The performance of wastewater treatment plants (WWTPs) is closely related to the structure and function of microbial communities which are frequently regulated by inoculating carbon source or new microbes. However, the status of microbial communities may be determined by the homeostasis of the bioreactors or properties of the influent especially in full-scale wastewater treatment plants. In this study, a full-scale packing-reinforced multistage biological contact oxidation process (PMBCOP) was used for investigating the durative impacts of carbon source addition and new sludge inoculation on the structure, stability and metabolic pathways of microbial communities. The results showed that inoculation of carbon sources or new sludge significantly increased the diversity (Chao1 and Shannon index) and reciprocal cooperations among microorganisms which further improved the stability of microbial communities and the COD (by 15%) and NH₃-N (by 3%) removal efficiencies. Proteobacteria and Bacteroidota were two dominant phyla in the system and were responsible for the main metabolic pathway, i.e. amino acid metabolism. Nevertheless, the modifications of key genera, stability, up-regulated metabolites and enriched metabolic pathways as well as the improved removal efficiencies were not able to persist. The resistant ability of microbial community declined after stopping adding carbon source and new sludge which resulted in the instability and low removal efficiencies of the PMBCOP and aroused the requirements on exploring deep homeostatic mechanism of microbial communities and new promoting strategies. This study provided new insights on the durative effects on the succession and metabolism of microbial communities combing with the performances of the full-scale wastewater treatment plant which is helpful for the management of full-scale WWTPs.