Effective enrichment of anaerobic ammonia oxidation sludge with feast-starvation strategy: activity, sedimentation, growth kinetics, and microbial community

[Display omitted] •The feast-starvation strategy is effective to enrich anammox sludge.•Limited nitrite supply alleviates the floating and loss of anammox sludge.•Boundary definitions were established for different modes of nitrite supply.•The growth rate of Candidatus_Kuenenia with specific feast-starvation up to 0.085 d-1. To address the issue of floating and loss of floc sludge caused by gas production in anaerobic ammonia oxidation (anammox) reactors, this study proposes a limited nitrite supply strategy to regulate gas production during the settling and enhance sludge retention. Results indicate that the effluent suspended solids in the anammox reactor can be reduced to as low as 0.11 g/L under specific feast-starvation conditions. Even under long-term intermittent nitrite-starvation stress, the maximum growth rate of Candidatus_Kuenenia can still reach 0.085d-1, with its abundance increasing from 0.47% to 8.83% within 69 days. Although the combined effects of starvation and sedimentation would lead to a temporary decrease in anammox activity, this reversible inhibition can be fully restored through substrate intervention. The limited nitrite supply strategy promotes the sedimentation of anammox sludge without significantly affecting its growth rate, and effective sludge retention is crucial for enriching anammox sludge during initial cultivation.