Integrated moving bed biofilm reactor with partial denitrification-anammox for promoted nitrogen removal: Layered biofilm structure formation and symbiotic functional microbes

Partial denitrification/anaerobic ammonia oxidation (anammox) (PD/A) is currently an advanced nitrogen removal process. This study developed a PD/A system in a moving bed biofilm reactor. Results showed that the nitrogen removal efficiency reached 76.60% with a COD/NO3-N of 2.0, and the contribution of anammox was 88.01%. Further analysis showed that the biocarriers could form layered pH and dissolved oxygen structures to promote the aggregation of different functional bacteria at various depths, thus stabilizing the coupled process. Microbial structure analysis showed that the abundance of Saccharimonadales, responsible for denitrification, increased from 0% to 36.27% between day 0 and day 120, while the abundance of Candidatus Jettenia, responsible for anammox, decreased from 10.41% to 2.20%. The synergistic effect of Saccharimonadales and Candidatus Jettenia enabled stable and efficient removal of nitrogen. This study proposed a novel configuration of the PD/A process and provided a theoretical basis for its promotion and application.