(130f) Understanding the Role of System Decoupling and Illumination on Nutrient Dynamics, Microbial Community, and Yield in Aquaponics

Aquaponics is a unique combination of aquaculture and hydroponics, where fish waste is used to grow food. The most widely used type of aquaponics is coupled aquaponics, a batch reactor that involves continuous water recirculation between the fish tank and the grow bed. There is a newer type of aquaponics called decoupled aquaponics, which involves separating the system into a one-way flow from the fish tank to the grow bed. This allows for efficient management of individual plant needs without compromising the health of the fish. Another important factor influencing aquaponics performance is light. Illuminating the fish tank can stimulate algal growth in the biofloc (the microbial community living in the fish tank), providing supplemental feed for filter-feeding fish and enhancing the nitrification rate, a crucial aspect of maintaining aquaponic stability.

This study investigated how system decoupling and fish tank illumination affect nutrient dynamics, microbial communities, and product yield. A full-factorial experiment assessed four aquaponics system types (dark-coupled, light-coupled, dark-decoupled, and light-decoupled) over nine months across spring and fall trials. The results indicated that both fish tank illumination (p = 0.020) and coupling of the fish tank and grow bed (p < 0.001) significantly increased Tilapia yield. Specifically, light systems and coupled systems demonstrated 84 g and 91 g higher fish yields, respectively, compared to the dark and decoupled systems. The combination impact of light and coupling was evident in the light-coupled system, resulting in ~550 g average fish weight which was about 150 g more than the next highest treatment (dark-coupled). We also observed fish feeding on algal biofilms in the light systems, contributing an additional protein-rich food source for Tilapia, which led to enhanced growth and a better feed conversion ratio.

Moreover, the light-coupled system showed superior tomato yield (4503 g/system) during the first trial. However, in the second trial, the continuous recirculation of water in coupled systems resulted in an overaccumulation of biosolids and a decrease in oxygen levels in the grow bed. This ultimately led to a decreased yield in the coupled systems. On the other hand, the light-decoupled system achieved the highest biomass of 8750 g/system in the second trial, demonstrating the impact of operating aquaponics in batch or semi-continuous modes on biosolids growth and nutrient transmission - crucial factors that affect the system's behavior. The findings suggest that operating the system in coupled mode during the initial four months, followed by a transition to a decoupled function could be an efficient solution for productive and sustainable aquaponic operations.