Robust aeration coefficient control based on pH feedback towards stable NO-N/NH-N ratio in large pilot-scale partial nitritation reactor treating food waste digestate.

Two-stage partial nitritation/anammox (PNA) system is a promising technology for treating food waste digestate (FWD). Maintaining a stable NO-N/NH-N ratio in partial nitritation (PN) is essential for the successful implementation of two-stage PNA. Although the aeration coefficient (AC) is a key regulatory parameter, its stability is challenged by fluctuations in chemical oxygen demand (COD). In this study, a robust AC control strategy based on pH feedback was developed to achieve precise PN ratio. The pH was negatively correlated with the ratio, with the optimal value achieved at pH 7.91. This strategy effectively mitigated the impact of COD variations, maintaining a stable NO-N/NH-N of 1.27 ± 0.10. Furthermore, the relative abundance of Nitrosomonas increased from 1.0 % to 24.2 %, ensuring stable PN performance. These findings highlight that integrating AC control with pH feedback is an effective approach to maintaining the NO-N/NH-N ratio, facilitating the engineering-scale application of two-stage PNA for FWD treatment.