Revealing the response of community structure and metabolic pathway to varying organic matter stress in a dissolved oxygen-differentiated airlift internal circulation partial nitritation-anammox system

In practice, the influent organic matter is often pre-treated to reduce the impact on partial nitritation-anammox (PNA) process. However, the influent organics may also drive the denitrification process and improve total nitrogen removal efficiency of the PNA process. Thus, we designed and operated a novel dissolved oxygen-differentiated airlift internal circulation PNA (PNA-DOAIC) system in this study at various influent C/N ratios of 0-4.0. Nitrogen removal perfor-mance, microbial activity and community, and metabolic pathways in response to varying organic matter stress were investigated via the continuous experiment combined with batch test. The results showed that the optimum in-fluent C/N ratio was 2.0 in this system, and the efficient and stable operation was still maintained at the C/N ratios of 0-3. At this time, the TN removal efficiency and removal rate could reach 95.1 % and 0.93 kg-N/m3/d, respectively, while COD efficiency remained at 95.4 %. Efficient removal performance was achieved via the PNA coupled with de-nitrification. However, the anammox bacteria (AnAOB) activity and abundance declined persistently as the influent C/ N ratio was further raised, and heterotrophic bacteria gradually replaced AnAOB as dominate genus. Meanwhile, met-abolic functions involving the material exchange and organic degradation were significantly enhanced. Nitrogen removal pathways changed from PNA to the nitrification-denitrification process. This study provides deep insights into effects of organic matter on the PNA process and can expand the application scope of this novel PNA-DOAIC bioreactor.

Automated summary

In this study, a novel dissolved oxygen-differentiated airlift internal circulation PNA (PNA-DOAIC) system was designed and operated to investigate the effects of organic matter on the PNA process. The results showed that an influent C/N ratio of 2.0 was optimal for efficient and stable operation. The PNA coupled with denitrification achieved high nitrogen removal efficiency, but as the influent C/N ratio increased, the activity and abundance of anammox bacteria declined, and heterotrophic bacteria became dominant. The nitrogen removal pathways shifted from PNA to the nitrification-denitrification process. This study provides important insights into the effects of organic matter on the PNA process and expands the application scope of PNA-DOAIC bioreactors.