Effects of exogenous nitrification sludge on the single-stage partial nitrification-anammox system of municipal sewage

In order to improve the nitrogen removal performance and stability of the single-stage partial nitrification-anammox (SPNA) system treating municipal sewage, the effects and mechanisms of adding exogenous nitrification sludge to mainstream SPNA system were evaluated under intermittent aeration condition. The results showed that the total nitrogen removal efficiency of the control SPNA system (SBR3) increased from 35.5% to 66.3%. The total nitrogen removal efficiencies of SPNA systems with nitrification sludge added in batches in a short cycle (SBR2, the dosing period was 5d, the dosing ratio was 2.5%) and in batches in a long cycle (SBR1, the dosing period was 5d, the dosing ratio was 2.5%) increased from 31.7% and 36.5% to 76.3% and 67.2%, respectively. And the addition of nitrification sludge was beneficial to the nitrogen removal performance of mainstream SPNA system and adding nitrification sludge in batches in a short cycle showed better performance. The maximum activities of anaerobic ammonium oxidation bacteria (AnAOB) in SBR1-SBR3 increased from 3.43mg-N/(L·h) to 7.66, 8.19% and 7.31mg-N/(L·h), respectively, and the activity ratios of ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) were 8.79, 9.83 and 8.78, respectively. Adding nitrification sludge under intermittent aeration condition could selectively inhibit NOB and enrich AOB, leading to a higher activity ratio of AOB and NOB and more stable partial nitrification, which provided stable substrates for AnAOB. In addition, adding the nitrification sludge in batches in a short cycle could reduce the impact of NOB of exogenous nitrification sludge on the system, which was more conducive to achieve high AOB/NOB activity ratio and improved the stability of system. Moreover, the relative abundance of Candidatus_Competibacter, thought to be the endogenous partial denitrification bacteria, increased obviously, providing AnAOB with more nitrite and was further beneficial to AnAOB enrichment. Therefore, this study provided new ideas for promoting the application of mainstream anammox process. © 2022 Chinese Society for Environmental Sciences. All rights reserved.