Careful design and management of RAS are the basis for a successful waste management with respect to both waste production and treatment. Operation of RAS under well controlled culture
conditions contributes significantly to an efficient feed utilization, hence, low waste production. Furthermore, proper incorporation of treatment procedures within the recirculating loop or in the effluent stream may further contribute to a significant reduction in waste production by these systems. In most indoor RAS, the bulk of waste produced by the fish is captured and removed in a concentrated effluent stream that may be treated onsite before final discharge. Such onsite treatment generally involves sludge thickening and flow stabilization but may also be designed to allow bacterial decomposition of solid waste. Outdoor RAS, mostly situated in warmer climates, are often operated with partial waste reduction within the recirculation loop. In the latter systems, phototrophic organisms such as plants and algae are
often involved in treatment of recirculation as well as of effluent water.