Nitrogen transformations in aquaponic systems: A review

Abstract

In recent years, aquaponic systems have gained significant popularity as soilless agriculture systems for organic fruits and vegetables production with concomitant remediation of aquaculture effluent. Aquaponics is a potential sustainable food production system that integrates aquaculture with hydroponics in which nitrogen-rich effluent from the fish production is utilized for plant growth. Because nitrogen is one of the most important inputs in an aquaponic system, it is critical to investigate the nitrogen transformations in the system for enhanced recovery of resources. Since studies on nitrogen transformations and nitrogen utilization efficiency (NUE) in aquaponic systems have been very limited, this review critically examines the important fates of nitrogen from input to outputs (e.g., ammonia nitrogen generation, nitrification, nitrate assimilation and nitrogen loss) to improve NUE in aquaponic systems. Various factors affecting the nitrogen transformations are also discussed. Furthermore, an example of nitrogen imbalance between nitrate uptake and nitrate generation rates in an aquaponic system was demonstrated. This review aims to advance our current understanding of nitrogen transformations and outlines future research needs in aquaponic systems, a sustainable model for efficient water and nutrient managements, and food production.

Growth and Nutrient Removal Efficiency of Sweet Wormwood (Artemisia annua) in a Recirculating Aquaculture System for Nile Tilapia (Oreochromis niloticus)

“…Dissolved oxygen (DO) levels were lower than 6.3-7.7 mg/L reported by [40] in an ebb and flood aquaponic system. The low DO levels could be attributed to the chemical transformation processes in the aquaponic system including fish respiration, production of high organic loads in the aquaponic system, activities of heterotrophs in addition to oxidation of nitrifying bacteria and oxygen absorption by plant roots [41,42]. Therefore, high DO levels should be maintained in these aquaponic systems for optimal plant growth.…”

“…Nutrient uptake by plants contributes significantly to the removal of nutrients from aquaponic systems [23]. However, the nutrient removal capacity of aquaponic plants is influenced by (1) the growth stage and nutrient needs of the plant and (2) the activity of ammonia-oxidizing bacteria in the aquaponic system [41,46]. Young plants have low nutrient requirements, but this increases during the vegetative growth [47].…”

“…The activity of the nitrifying bacteria can explain the ammonia, nitrate and nitrite trend in the aquaponic system. The nitrifiers play a significant role in the removal of nitrogen in media-based aquaponic systems [14,41]. The nitrifying bacteria are naturally slow growing and can take a long period to establish and multiply [49].…”

Hydroponic systems and water management in aquaponics: a review

“…The optimisation of these parameters in AP is important considering that if low hydraulic load rate leads to oxygen deficiency and enables denitrification and N2 volatilisation, high hydraulic load rate reduces the contact time between water and roots (Wongkiew et al, 2017). A question arises as to whether it is more important the water recirculation frequency in the fish tanks or the water flow speed through the roots bringing fresh molecules.…”

Risk analysis model in aquaponics

“…• Fish density and pathogen control The quality of cultivation also depends on the density of the biomass. It is kept below 50 kg / m3 for the wellbeing of cultivation and for optimizing production [15], [17].…”