Rapid in-situ recovery of starved anammox consortia: Metabolic stimulation and microbial synergy driven by organics and oxygen.

Starvation stress severely reduces anammox activity, yet there remains a lack of simple, in-situ, and easily implementable strategies to effectively restore the metabolic activity of starved anammox sludge. This study developed a straightforward and sustainable route for anammox activity recovery by investigating the performance and metabolic responses of anammox consortia. The results show that simply supplementing organics at a C/N ratio of 0.3, together with residual dissolved oxygen, successfully restored the anammox activity of starved sludge, achieving a nitrogen removal efficiency of 83% and a specific anammox activity recovery rate of 88.99% after 30 days. Correlation analysis further reveals that higher intracellular H2O2 levels promoted anammox activity, rather than the relative abundance of Candidatus Kuenenia. Starvation stress decreased the relative abundance of Ca. Kuenenia from 36.96% to 27.20%, which further declined to 25.60% during the recovery period. The recovery of anammox activity is attributed to enhanced anammox bacterial metabolism, including extra electron shuttling, and microbial interactions, such as NO/nitrite feeding by Thauera sp. 017997795 and sp. M3007. These findings highlight the effectiveness of moderate carbon supplementation in restoring anammox performance, and more importantly, offer a practically valuable, easy-to-operate strategy for engineering applications where simple and rapid recovery from starvation is urgently needed.