[Start-up and Recovery Performance of ANAMMOX Reactors Under Long-term Starvation]

The application of ANAMMOX technology is constrained by sluggish growth and difficulty in enriching ANAMMOX bacteria. Long-term starvation of functioning bacteria due to limited substrate supply makes the steady operation of ANAMMOX reactors more difficult. Re-examining the start-up and recovery performance of the ANAMMOX reactor and identifying its resistance mechanism are important from the standpoint of long-term starvation. By inoculating nitrifying and denitrifying sludge under various operating circumstances, the ANAMMOX reactors were successfully started. Under various start-up procedures, the tolerance mechanism and recovery performance were examined. The outcomes demonstrated that the denitrifying sludge-inoculated reactor operated steadily with a high substrate concentration and low flow rate. After 85 days of operation, the removal efficiencies of NH₄⁺-N, NO₂^--N, and total nitrogen reached 98.7%, 99.3%, and 89.3%, respectively. After 144 days of starvation and 30 days of recovery, the better nitrogen removal performance was achieved at a low substrate concentration and high flow rate, and the removal efficiencies were 99.8% （NH₄⁺-N）, 99.8% （NO₂^--N）, and 93.6% （total nitrogen）. During the starvation, extracellular polymeric substances wrapped the ANAMMOX bacteria and kept them intact to resist long-term starvation stress. The expression of nirS, hzsA, and hdh genes ensured the synthesis of nitrite/nitric oxide oxidoreductase, hydrazine synthase, and hydrazine dehydrogenase to maintain ANAMMOX activity. There was no significant difference in the relative abundance of ANAMMOX bacteria before and after starvation recovery. Candidatus Kuenenia had better anti-hunger ability, and the relative abundance increased by more than 86% after 30 days of recovery, confirming its tolerance to long-term starvation.