Stoichiometric analysis and control strategy of partial nitrification for treating dewatering liquid from food-waste methane fermentation

Abstract

Methane fermentation is critical for food-waste management; however, effective treatment of its high-ammonium dewatering liquid remains a major challenge. Anammox, a promising candidate for liquid treatment, requires effective pretreatment, such as partial nitrification (PN), to reduce ammonium and generate sufficient nitrite to optimize efficiency. In this study, an airlift reactor was employed to process the dewatering liquid from food-waste methane fermentation. Stable operation for over 360 days demonstrated its feasibility under high-load conditions. By implementing precise aeration control strategy to stabilize the ammonium removal efficiency (ARE = 50.2–57.1%), a detailed summary of the optimal operational parameter ranges (consumed inorganic carbon [ΔIC] 1000–1160 mg C/L, effluent [Eff.] IC 282–378 mg C/L, pH 8.05–8.17, Eff. Alkalinity 1000–1350 mg CaCO₃/L, free ammonia 61.9–82.5 mg/L, and free nitrous acid 47.6–71.1 μg/L) were provided under the ideal NO₂⁻/NH₄⁺ ratio of 1.1–1.3. Additionally, variations in ammonium oxidizing bacteria activity with temperature and pH were analyzed by the Arrhenius, cardinal temperature model with inflection, and Haldane models, with R² values of 0.998, 0.975, and 0.999, respectively. Results suggest that the optimal conditions for partial nitrification were identified as a temperature range of 20–40°C and a pH range of 7.5–8.5. Microbial sequencing reveals Nitrosomonas markedly enriched during operation, with its abundance rising from 3.67% to 9.76% as the NLR increased. Notably, NOB was nearly undetectable throughout the entire process. Additionally, an advanced aeration-based control mechanism with a positive feedback loop were proposed, which allows the airlift PN reactor to effectively treat high-ammonia dewatering liquid, thereby providing a suitable influent for subsequent anammox and offering crucial theoretical insights for future controlling pilot-scale system operation.