Long-term stability of reactor microbiome through bioaugmentation with Alcaligenes aquatilis AS1 promotes nitrogen removal of piggery wastewater.

Bioaugmentation is considered as an attractive method for nitrogen removal in water treatment, but its effectiveness in actual high-strength piggery wastewater has not been adequately verified and the mechanism of bioaugmentation in actual wastewater treatment system is not very clear especially from the perspectives of microbial communities and functional genes. This study investigated the mechanisms of a heterotrophic nitrifying-aerobic denitrifying strain Alcaligenes aquatilis AS1 in the bioaugmentation of continuous biological nitrogen removal of actual piggery wastewater at laboratory scale. The addition of strain AS1 significantly improved the nitrogen removal efficiency (more than 95% of NH-N and 75% of TN were removed) and raised the activated sludge resistance to shock loading. AS1 addition also significantly shifted the microbiota structure and interactions among microbial networks were enhanced to obtain the stable bacterial communities. Moreover, strain AS1 achieved effective proliferation and long-term colonization in activated sludge with a relative abundance of genus Alcaligenes more than 70% during the whole operation process and played a dominant role in biological nitrogen removal, while different genera were respectively enriched and involved in pollutants removal at different stages in the control group. In addition, the abundances of most functional genes involved in carbon (C) degradation, carbon fixation and nitrogen (N), phosphorus (P), sulfur (S) cycling in activated sludge were significantly increased in reactor AS1, indicating that strain AS1 not only relied on its unique C and N metabolic activities, but also recruited microorganisms with diverse functions to jointly remove pollutants in wastewater, which could be a common bioaugmentation mechanism in open reactors. This study proves the promising application prospect of strain AS1 in the treatment of high-strength piggery wastewater and shows great importance for guiding bioaugmentation application of functional strains in practical wastewater treatment systems.