Isolation and screening of indigenous nitrifying bacteria to enhance nutrient recovery in an aquaponics system

Abstract

The recycling processes of aquaponic waste into fertilizers are highly dependent on the type and activity of nitrifying bacteria in the system. This study aims to find indigenous nitrifiers to enhance nutrient recovery in an aquaponics system. Twelve indigenous nitrifiers consisting of ammonia and nitrite-degrading bacteria were isolated from a local earthen pond of Nile tilapia (Oreochromis niloticus), and two isolates (AQ4 and AQ12) were selected due to their highest capacity to degrade either ammonia or nitrate respectively. Based on the 16S rRNA gene sequences, these isolates were identified as Marinobacter nauticus (AQ4) with 98.64% similarity, and Bacillus sp. (AQ12) with 99.89% similarity. When these bacterial isolates were applied in aquaponics systems with bacterial enhancement (aquaponicsBE), the nutrient recovery was significantly higher compared to the control (aquaponicsctrl), indicated by a 500 g higher total harvested biomass. With a significance value of p < 0.05, aquaponicsBE gives 17% higher crude fat and protein retention in vegetables while in fish 14% higher crude fat was found. Energy retention in vegetables was 23% higher than in the control. Furthermore, fish grew better in the aquaponicsBE system, with 0.6%BW/day higher specific growth rate, and 0.05 better feed conversion ratio compared to that of fish reared in the control.