Navigating towards Decoupled Aquaponic Systems: A System Dynamics Design Approach

TLDR

Aquaponics couples fish and plants by recirculating nutrient‑rich water, but achieving optimal conditions for both species simultaneously is difficult. This study proposes a decoupled aquaponic system (DAPS) and models its water, nutrient, fish, sludge, and plant dynamics. A dynamic model was built using literature data from aquaculture, hydroponics, and sludge treatment to simulate the system. The model shows that water quality depends on hydroponic evapotranspiration, that one‑way flows accumulate remineralized nutrients to benefit plants, and that cultivation area should be sized to phosphorus availability, a key limiting factor.

Abstract

The classical working principle of aquaponics is to provide nutrient-rich aquacultural water to a hydroponic plant culture unit, which in turn depurates the water that is returned to the aquaculture tanks. A known drawback is that a compromise away from optimal growing conditions for plants and fish must be achieved to produce both crops and fish in the same environmental conditions. The objective of this study was to develop a theoretical concept of a decoupled aquaponic system (DAPS), and predict water, nutrient (N and P), fish, sludge, and plant levels. This has been approached by developing a dynamic aquaponic system model, using inputs from data found in literature covering the fields of aquaculture, hydroponics, and sludge treatment. The outputs from the model showed the dependency of aquacultural water quality on the hydroponic evapotranspiration rate. This result can be explained by the fact that DAPS is based on one-way flows. These one-way flows results in accumulations of remineralized nutrients in the hydroponic component ensuring optimal conditions for the plants. The study also suggests to size the cultivation area based on P availability in the hydroponic component as P is an exhaustible resource and has been identified one of the main limiting factors for plant growth.