Oxygen Transfer and Ammonia Nitrification Modeling for Aeration Optimization in Integrated Biofilm–Membrane Recirculating Aquaculture Systems

Abstract

Recirculating Aquaculture System (RAS) is an aquaculture technology capable of maintaining water quality through recirculation and biological treatment processes. One of the main challenges in this system is ammonia control, which can affect fish health and water quality stability. This study evaluated three experimental airflow conditions (100, 150, and 190 L/min) and simulated additional airflow scenarios from 80 to 220 L/min using a Monod-based nitrification model. The research methodology involved the development of a Monod kinetics-based mathematical model considering the effects of NH3, dissolved oxygen (DO), alkalinity, temperature, and pH on the activity of ammonia oxidizing bacteria (AOB). The results showed that increasing airflow enhanced DO concentration, resulting in more effective nitrification and lower NH3 effluent concentration. Model validation showed the strongest agreement at an airflow of 190 L/min, with R2 of 0.923 and RMSE of 0.049 mg/L, indicating that the calibrated model captured the observed NH3 effluent trend under this operating condition. Although higher airflow improved oxygen availability, the highest percentage NH3 removal was observed at 150 L/min, while 190 L/min produced the lowest effluent NH3 and the best model fit under a lower influent load.