Integration of down-flow hanging sponge reactor to <italic>oreochromis niloticus</italic> − <italic>Brassica oleracea</italic> aquaponics system.

AbstractAquaponics is a promising solution for addressing food security concerns. Nonetheless, an effective water-purification system is necessary to achieve high and stable yields of fish and vegetables. This study aimed to evaluate the nitrification and oxygen transfer performance of a laboratory-scale down-flow hanging sponge (DHS) reactor with <italic>a Brassica oleracea</italic> aquaponics system to treat water in an <italic>Oreochromis niloticus</italic> closed-aquaculture system. The DHS reactor showed a higher oxygen transfer coefficient (<italic>KLa)</italic> than the conventional aerator and provided an adequate dissolved oxygen (DO) concentration of approximately 5.5 mg/L essential for <italic>O. niloticus</italic> growth throughout the experimental period. The evaluated DHS-based aquaponic system maintained high water quality in an aquaculture tank, with a survival rate of 97%. The <italic>O. niloticus</italic>grew at a low feed conversion ratio of 1.5–2.1 and a low feeding rate of 0.5% at high stocking densities of 17.5–22.2 kg-fish-weight/m3. 16S rRNA gene sequencing indicated that the DHS sponge carrier effectively retained nitrifying bacteria such as <italic>Nitrosomonas</italic> and <italic>Nitrospira</italic>. This study demonstrated that the DHS reactor provided a high DO concentration and that a simultaneous DHS reactor with a hydroponic tank provided a low-cost aquaponic system that could be applied for food production in the aquaculture industry. [ABSTRACT FROM AUTHOR]