Linear modelling of the mass balance and energy demand for a recirculating aquaculture system

This work seeks to understand the predominant drivers affecting energy demand for a recirculating aquaculture system (RAS) by developing a numerical model in Matlab coupled with Aspen HYSYS and validating against measurement data for a case-study site. 15 weeks of RAS operation were simulated to replicate the grow-out of Atlantic salmon (Salmo salar) from 42.5 to 322 g body weight (BW). Data on water quality parameters and the energy demand of the RAS and its equipment were generated. The water treatment loop was automated from Matlab, along with simulation of the fish tanks. Parameters were continuously updated during the quasi-steady dynamic simulation of the RAS and data was stored. Concentrations of oxygen, carbon dioxide, total ammonia nitrogen, total suspended solids and nitrate nitrogen in the fish tanks were recorded for the full 15 week grow-out. The specific energy demand of the RAS was calculated at 9.59 kWh/kg for the full grow-out. In total, 664 MWh were needed for the complete RAS operation. Coupling Matlab and Aspen HYSYS is a viable method for modelling and simulating a RAS. The presented tool can also simulate abrupt changes in the system (such as a power outage) and resume normal operation once power is restored.