Water flow is the mechanism by which oxygen is transported into a fish culture vessel and the waste products being generated within are removed. The design of a recirculating aquaculture system (RAS) should ensure that the important parameters affecting water quality and fish productivity, e.g., oxygen, ammonia, carbon dioxide, and suspended solids are properly balanced. This requires calculating the value of each of these parameters independently to determine the thresholds for each. Then, having done the necessary calculations, the system must be operated at the lowest flow rate possible while still maintaining a particular parameter at its design value, e.g., ammonia. The simple word equation is:
Transport in of "x" + production of "x" = transport out of "x" (3.1)
The production or P term can be the production of oxygen, ammonia, suspended solids, or CO2. Design examples will be given.
A mass balance is depicted in Figure 1 for the general case where part of the flow is recirculated and part of the flow is flow-through.