In aquaponics systems, liquid effluent from fish culture is not enough to meet the nutritional requirements of plants. In this study, an aquaponics system coupled with an aerobic digestion bioreactor (ADBR) for the digestion of the Nile tilapia (Oreochromis niloticus) sludge was designed in triplicate. The aerobic digestion of fish sludge was performed using biofertilizer containing phosphate-solubilizing bacteria (PSB) (Pseudomonas putida strain P13 and Pantoea agglomerans strain P5; 107 CFU/mL for each bacterium) at a levels of 0.1 % for 14 days in the ADBR. Nile tilapia (O. niloticus) fish and peppermint (Mentha × piperita L.) plant were cultivated in two aquaponics (AP) systems for six weeks without and with adding liquid organic fertilizer (LOF) produced from the aerobic digestion of fish sludge as control and AP-LOF treatment, respectively. The use of PSB for aerobic digestion of the fish sludge led to increasing the PO43-, K, Fe, Zn, Cu, and Mn concentrations compared to the control (p < 0.05). The electrical conductivity (EC) of the LOF increased significantly with adding PSB compared to the control (p < 0.05). The final body weight of Nile tilapia increased by 81.82 % and 104.17 % in the AP and AP-LOF treatments after six weeks, respectively. The food conversion ratio (FCR) improved in the AP-LOF treatment compared to the AP treatment (p < 0.05). The total ammonia nitrogen (TAN) and nitrate concentrations decreased in aquaponic water with adding the LOF compared to the AP treatment (p < 0.05). The biomass and morphological traits of peppermint, including fresh weight of plant, and aerial parts, shoot height, number of leaves, and nodes per plant increased in the AP-LOF treatment compared to the AP treatment (p < 0.05). The P, K, Na, Ca, and Fe contents of peppermint cultivated in the AP-LOF treatment were higher than in the AP treatment (p < 0.05). In conclusion, the use of PSB in the ADBR unit of aquaponics system improved the nutrient recovery from Nile tilapia sludge and adding liquid organic fertilizer to aquaponic water had a positive effect on the growth performance of Nile tilapia and peppermint plant.

Keywords