Design and function of a nitrogen and sediment removal system in a recirculating aquaculture system optimized for aquaponics

Aquaponic systems (APSs) are based upon the sustainable utilization of nitrogen and phosphorus from a recirculating aquaculture system (RAS) as the nutrient source for plant production. Since the proper management of nitrogen and suspended solids are important for nutrient utilization efficiency, their optimization was evaluated. The RAS integrated with filtration unit and nitrifying biofilter provided complete nitrification without solid accumulation. Under the optimal treatment condition for 16 d, the treated water was low in ammonia (0 mg-N/L) and high in nitrate (> 6 mg-N/L) concentrations, which was appropriate for use in the cultivation of lettuce (Lactuca sativa). The RAS was then incorporated with hydroponics at a 5:1 fish: plant weight ratio. Moreover, the simplified APS was compared with a typical APS system that incorporated filtration unit and nitrifying biofilter. The natural growth of nitrifying microorganisms in the simplified APS could perform complete nitrification after 20 d of operation giving low ammonia and nitrite concentrations. The nutrient removal efficiency of the simplified APS resembled the typical system. During the aquaponics, the hydroponic unit in the aquaculture system was sufficient to control the nutrient concentrations within the appropriate levels for fish cultivation, i.e. nitrate (< 20 mg-N/L) and phosphate (< 3 mg-P/L).