Steady-state and dynamic model for recirculating aquaculture systems with pH included

In this work, simplified steady-state and dynamic models of a Recirculating Aquaculture System (RAS) of Atlantic salmon (Salmo salar) are described. The RAS process under study includes a fish tank, a biofilter, a CO₂ stripper, and an oxygen cone. Compared to existing models, the main contribution is that it explicitly models the pH, by using reaction invariants such as total inorganic carbon (TIC), total ammonia nitrogen (TAN), and alkalinity. As the possibility of placing the pH/alkalinity adjustment (base or buffer addition) into the fish tank or into the biofilter was considered, four steady-state scenarios were studied, where one of the adjustments is utilized in each scenario. A dynamic simulation of the process with oxygen and pH controllers was performed and compared with commercial RAS production data, and what adjustments had to be done to get an agreement between the model and the plant data.