Flow-through aquaculture systems greatly demand water resources because of the large volumes of high-quality source water required to rear fish and the discharge of wastewater into the aquatic environment. In particular, the discharge of untreated aquaculture wastewater can lead to physicochemical and biological degradation of the receiving waters. Despite advances in feed quality and feeding practices, the treatment of wastewater from flow-through aquaculture facilities has lagged considerably.
In this study, a novel low-water exchange aquaculture system was developed to reduce the excessive water exchange rate and solve persistent water quality problems in the traditional flow-through aquaculture systems. The improved aquaculture system was designed to reduce the water exchange rate from 24 cycles per day to 8–9 cycles by including a CO2 vacuum degassing tower equipped with a degassing media. In addition, this system recovered approximately 70 % to 80 % of the heat discharged from the aquaculture tank from the inflow water through a heat exchanger. The insufficient heat source (20 % to 30 %) was supplied using a heat pump to control the optimal water temperature of the aquaculture tank. Thus, productivity could be maximized. This system consists of a solids (50 μm) treatment unit, Ag-NPs impregnated filtration + CO2 vacuum degassing tower, heat exchange device, heat pump, and influent filtration and disinfection system (ultraviolet device).
The aquaculture system developed in this study was established using mass balance relations. The aquaculture system can be operated with only 30–45 % of the flow rates used in traditional flow-through systems. The system saves energy and maintains total ammonia nitrogen (TAN) and CO2 concentrations in each aquaculture tank below 2 mg/L and 7 mg/L, respectively. This system is expected to reduce the mortality rate of farmed fish by improving the efficiency of water treatment devices. The next step would be to evaluate the maximum load of TAN and CO2 generated when cultivating Paralichthys olivaceus in the traditional and modified flow-through aquaculture systems and perform experimental and numerical analysis to investigate whether such a system could be incorporated effectively in the aquaculture industry.