The aquaponic principle—It is all about coupling

Abstract

The aquaponic principle is the coupling of animal aquaculture (e.g. fish) with plant production (e.g. vegetables) for saving resources. At present, various definitions of aquaponics exist, some bearing the risk of misinterpretation by dismissing the original meaning or being contradictory. In addition, there is no standard terminology for the aspects of coupling between the aquaponic subsystems. In this study, we addressed both issues. (1) We developed new or revised definitions that are summarised by: Aquaponic farming comprises aquaponics (which couples tank‐based animal aquaculture with hydroponics) and trans‐aquaponics, which extends aquaponics to tankless aquaculture as well as non‐hydroponics plant cultivation methods. Within our conceptual system, the term aquaponics corresponds to the definitions of FAO and EU. (2) A system analysis approach was utilised to explore different aquaponic setups aiming to better describe the way aquaponic subsystems are connected. We introduced the new terms ‘coupling type’ and ‘coupling degree’, where the former qualitatively characterises the water‐mediated connections of aquaponic subsystems. A system with on‐demand nutrient water supply for the independent operating plant cultivation is an ‘on‐demand coupled system’ and we propose to deprecate the counterintuitive term ‘decoupled system’ for this coupling type. The coupling degree comprises a set of parameters to quantitatively determine the coupling's efficiency of internal streams, for example, water and nutrients. This new framework forms a basis for improved communication, provides a uniform metric for comparing aquaponic facilities, and offers criteria for facility optimisation. In future system descriptions, it will simplify evaluation of the coupling's contribution to sustainability of aquaponics.

Causal Relations of Upscaled Urban Aquaponics and the Food-Water-Energy Nexus—A Berlin Case Study

“…Aquaponics is the coupling of recirculating aquaculture systems (RAS) and hydroponics (HP) and a key feature is the dual use of water, which was first used to raise the fish and then to fertigate the plants [21,39]. A recent life cycle assessment (LCA) compared AP crop production with an available market mix in the Berlin metropolitan area consisting of imported and locally produced lettuce and tomatoes (Mix-DE) [41] referred to in this study as comparative-LCA.…”

“…The packed and market available products originated from various countries and the respective transports to Berlin and storage were included. For the comparative-LCA, a simulation of an on-demand coupled AP [39] with a greenhouse size of 5000 m 2 , variable RAS size, and year-round production was used. The comparative-LCA scenario DAPS-R+ is characterised by rooftop aquaponics (here referred to as rooftop-AP) and active waste heat recovery [59] from the building below; an example of an existing rooftop AP is the Abattoir farm at the Anderlecht district of Brussels [60,61].…”

“…One design goal for the upscaled AP scenario was to enforce the aquaponic principle [39] for the total demand identified in the Berlin case study conducted here. In order to achieve this goal, fish production was balanced with vegetable production across all professional AP facilities so that there was no excess production or unnecessary effluent on either side.…”

“…AP is itself an NBS and the wastewater generated in the RAS, instead of being treated, can be provided as nutrient water for, e.g., a vertical green system (VGS) [79]. Systems based on the aquaponic principle that extend crop production from hydroponic to soil-based methods are referred to as trans-aquaponics [39]. Such a trans-aquaponic solution emerges when the two NBS units, in this case aquaculture and VGS, are coupled to tackle circularity challenges in cities [40].…”

“…There is a need for upscaling NBS and, inter alia, the promotion of sustainable agriculture and food systems is suggested by the UN [38]. Aquaponic farming, which comprises AP and trans-aquaponics [39], is considered an NBS unit [40] and should be addressed as well in tackling the issue of whether and under what conditions it makes sense to scale up urban aquaponics. In order to understand its system dynamics, it is necessary to investigate the dependencies and causal relationships of variables by systems analysis.…”