Rapid anammox startup in response to nitrogen loading variations: Reactor performance, microbial dynamics and mechanism exploration

The slow growth and reproduction of Anammox bacteria limited the large-scale popularization and application. To explore the quick start-up strategy for Anammox process, an exceptional nitrogen loading rate (NLR) of 0.229–0.548 kgN/(m3·d) was controlled by gradient-reducing hydraulic retention time (HRT) from 8 h to 5 h. NLR showed closed relation with nitrogen removal rate (NRR), where TN removal (ReTN) increased from 76.45 % to 81.88 % as NLR varying around 0.268–0.320 kg N/(m3·d) but declined to 64.66 % under NLR of 0.548 kg N/(m3·d). Kinetics models proved that the modified Logistic, Gompertz and Boltzmann models could well describe ReTN, with the maximum NRR (NRRmax) reaching to 0.428–0.576 kgN/(m3·d). Besides, lessened particle size (291.1 → 184.9 μm) was accompanied by sludge loss (3310 → 2320 mg/L) as NLR ascending, owing to the decreased tight-bound extracellular polymeric substances (T-EPS) fraction and protein/polysaccharide (PN/PS) ratio. Candidatus_Kuenenia known as the dominant Anammox bacteria climbed from 2.54 % to 16.50–17.93 %, symbolizing the successful achievement for Anammox startup. It suggested a possible start-up strategy via elevating NLR for mainstream Anammox, and the findings highlighted the potential implication for coupled partial denitrification (PD)-Anammox towards energy-efficient operation.