Rapid construction of granular activated carbon (GAC)-enhanced anaerobic ammonia oxidation system and study on the mechanism of systematic nitrogen removal

To address the problem of slow start-up of anaerobic ammonia oxidation (anammox) system, this study rapidly constructed an anammox system by granular activated carbon (GAC) reinforcement. The results indicated that under the optimal conditions, the GAC reactor successfully started up in 58 days. Compared with the control group, the lag phase, propagation phase and total start-up period were shortened by 17 days, 23 days and 20 days respectively. When the influent ammonia nitrogen concentration was increased to 100 mg/L and 200 mg/L, the removal rates of ammonia nitrogen and nitrite nitrogen in the GAC reactor were both above 90 %, and it took only 101 days to reach a nitrogen removal rate (NRR) of 0.70 kg-N/(m3 & sdot;d), which was 41 days faster than the control group. Further studies showed that the addition of GAC significantly increased the content of extracellular polymers (EPS), while greatly reducing the activity of Dehydrogenase (DHA). Additionally, anaerobic ammonia-oxidizing bacterium Candidatus Brocadia was successfully enriched, with a relative abundance of 30.30 %, confirming the process advantages of GAC modification. The present study investigated the critical operational parameters and metabolic interaction mechanisms for the rapid start-up of the anammox system, thereby establishing a robust theoretical framework for its engineering application.