Biological nutrient removal by recirculating aquaponic system: Optimization of the dimension ratio between the hydroponic & rearing tank components

• Marble goby, a high value fish, was cultured in a recirculating aquaponic system.
• Component ratio (hydroponic tank volume: rearing volume) was varied.
• High component ratio increases nutrient removal, fish and vegetable yield.
• 3 m3/m3 of component ratio shows high production of marble goby and water spinach.
• Recirculating aquaponic system shows potential for biological nutrient removal.

Marble goby (Oxyeleotris marmorata Bleeker) was cultured in a recirculating aquaponic system (RAS) containing a hydroponic tank grown with water spinach (Ipomoea aquatica). The influence of component ratio (hydroponic tank volume to rearing tank volume) on the fish growth, vegetable yield, and nutrient removal was investigated. Increased fish growth (2.4 g/day), vegetable yield (22 kg/harvest), and nutrient removal (83% ammonia-N removal, 87% nitrite-N removal, 70% nitrate-N removal, 60% removal of total phosphorus, 88% removal of total suspended solid, 63% removal of 5-day biochemical oxygen demand) were observed at high component ratio (3 m3/m3). Component ratio was found to have a significant influence on nutrient removal and production of marble goby and water spinach in RAS. A component ratio of ≥3 m3 of hydroponic tank volume to 1 m3 of fish rearing tank volume showed advantages in improving the production of the fish and vegetable and removing the nutrient wastes, TSS, and BOD5 generated from the culture of the fish. The results indicate that RAS show exceptional promise as a means to the reduction of biological nutrients accumulated in aquaculture wastewater and in turn providing a good water quality environment for fish culture.