Operational control mechanism and pilot-scale demonstration of integrated fixed-film activated sludge partial nitritation/anammox system

Integrated fixed-film activated sludge (IFAS) and one-stage partial nitritation-anammox (PN/A) are considered the optimal combination for wastewater nitrogen removal. However, pilot-scale studies on IFAS-PN/A processes remain scarce, which may be attributed to the lack of practically feasible control strategies. This study evaluated the potential of implementing different control strategies in a one-stage IFAS-PN/A pilot plant. The results showed that combining intermittent aeration with low dissolved oxygen (DO) was insufficient to meet ammonia-oxidation demands under mainstream conditions, while implementing an integrated control strategy that combined mixed volatile suspended solids (MLSS), pH, and DO regulation, favorable nitrogen removal efficiency of 73.1-92.8% was achieved for treating wastewater with nitrogen concentrations ranging from 100 to 5000 mg N/L. Correlation analysis and structural equation modeling revealed that controlling MLSS and the aeration coefficient is effective for ensuring adequate ammonium oxidation, whereas pH and ammonia oxidation rate (AOR)/ nitrogen loading rate (NLR), which better capture inter-parameter dynamics, serve as suitable indicators for process regulation and decision-making. Therefore, a multi-parameter control scheme integrating MLSS, aeration coefficient, pH, and AOR/NLR on top of intermittent aeration and DO control was demonstrated to achieve effective NOB suppression and enhanced performance across a wide concentration range.