Abstract
The SAD (Simultaneous Anammox and Denitrification) process combines anammox with denitrification to achieve nitrogen removal and carbon reduction. In this study, the flocculent activated sludge in the secondary sedimentation tank of the traditional sewage treatment plant was used as the research object. Under the action of high NH4+, adding reflux, and adjusting HRT in the UASB reactor, the transformation from flocculent sludge to SAD granular sludge was quickly realized. The results showed that a relatively stable SAD granular sludge system could be formed after 250 days of operation, and the system with reflux was more resistant to changes in the external environment than the system without reflux. In the SAD system, TN Removal Rate (TNRE) ≈ 90 %, Carbon Removal Rate (CRR) ≈ 90 %. After 3D-EEM, FTIR, and analysis of protein secondary structure, it was found that the particle stability and aggregation of the SAD stage were significantly improved compared with the previous two stages. The bacterial community structure had obvious vertical heterogeneity, mainly AnAOB (Ca. Kuenenia≈30 %) and denitrifying bacteria (Comamonas≈20 %). When the temperature drops sharply, the performance of SAD can be effectively restored by adding reflux and reducing the carbon source.
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