Aquaponik zur Selbstversorgung in der Kreislaufstadt: Begriffsbestimmungen, Bedarfsdeckung, Umweltauswirkungen, Systemanalysen und Standortpotenziale unter Berücksichtigung des Umlands - Fallstudie Berlin

• Aquaponics for self-sufficiency in the circular city: definitions, demand coverage, environmental impacts, system analyses and site potentials taking the peri urban area into account - case study Berlin

Baganz, Gösta F. M.; Lohrberg, Frank (Thesis advisor); Kloas, Werner (Thesis advisor)

Aachen : RWTH Aachen University (2022, 2023)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2022, Kumulative Dissertation

Abstract

Almost all future growth in the world's population will take place in urban areas, so that by 2050 about 68% of the world's population and 88.4% of the population in high-income countries will live in cities (UN, 2019). At the same time, global food production, including pre- and post-production, is responsible for approximately 21 - 37 % of net anthropogenic greenhouse gas emissions, accelerating global surface temperature rise (IPCC, 2021). Therefore, our current food systems need to be made more sustainable and at least partially embedded in urban space. The concepts of the circular city offer a suitable framework for this. One resource-efficient technology that can play a role in this is aquaponics, the production of fish and plants, which saves water, nutrients and energy through the synergistic coupling of a recirculating aquaculture system with hydroponics. The aim of this dissertation is to make a theoretical contribution to the transformation of the food system in this context by evaluating the potential of aquaponics for urban regions and thus to contribute to the promotion of sustainable urban development, thereby gaining knowledge on the research fields of aquaponics, circular cities and urban and regional planning. Moving the production of freshwater fish, lettuce and tomatoes through aquaponics to a city like Berlin could significantly reduce the environmental impact. Yet self-sufficiency does not necessarily mean sustainability. For one thing, the physical, economic and organisational parameters change with the size of a plant, and so does the environmental impact per unit of production. For another, energy sources from the circular economy must be included in order to make the shift in production sustainable. For this work, existing conflicting definitions of aquaponics were discussed and a revised taxon of "aquaponics" was presented based on a sound and justified definition. Additional new terms are proposed: trans-aquaponics and aquaponics farming (as a generic term for aquaponics and trans-aquaponics) as well as coupling type and coupling degree. Terms are also proposed for the circular economy and circular city in order to better conceptualise these research areas, including the generic term entity for the nodes of the circular network. Here, spatial identifiers were specified and considerations were made about the system boundary of the circular city. In order to be able to represent the elements of a circular economy network topology in a uniform way, an information model for nature-based solutions and connecting resource flows was developed. Ecological, socio-economic, cultural and political factors that determine aquaponics farming in a city region were presented from a systems analysis perspective. In this work, it was determined that the 3.77 million inhabitants in Berlin will require 21 kilotonnes (kt) of freshwater fish and fish products, 108 kt of fresh tomatoes (also for tomato products) and 27 kt of lettuce on the demand side in 2020. To meet this demand, on the supply side, about 370 intra-urban (0.6 ha) or 16 peri-urban (14 ha) aquaponics facilities are required, each with a total area of 224 hectares. A sufficiently large number of buildings have been identified that are suitable in terms of size, function and geometry to accommodate intra-urban aquaponics facilities. A reduction in negative environmental impacts was found in all LCA impact categories investigated for vegetable production (supply side) in optimised rooftop aquaponics. In terms of water consumption, aquaponics production would save about two million m³ of water compared to the status quo. On the demand side, a change in dietary habits towards an increased share of freshwater fish is discussed. It has been shown that larger-scale aquaponics application can reduce the ecological footprint of cities like Berlin and increase their resilience in terms of food security. Significant causal chains were identified for a relocation of production to Berlin with regard to the food - water - energy nexus. The strain on the natural water balance would decrease in Almería (Spain), but increase in Berlin. There is a lot of competition for use both on the ground and on the roofs in Berlin and thus a high pressure on the limited available space, which would increase through the implementation of aquaponics. The spatial impact of the facilities is mediated by their structures: building-integrated facilities in the intra-urban space and large, free-standing halls in the peri-urban space. Weighty reasons have been compiled that speak for aquaponics in an urban context, including: • The use of energy resources of the circular city. • The zero net land use of building-integrated aquaponics. • Low impact on transport. On the other hand, there are arguments against it, such as low economies of scale, which lead to reduced revenues, and intensive utilisation pressure, which is associated with higher costs. After weighing up the advantages and disadvantages, it seems sensible to consider further locations in the city's hinterland. The aim is to use peri-urban areas without giving up the benefits of aquaponics in intra-urban areas. Options are: • Sustainable energy supply, which could be achieved in the cold season through decentralised solutions and grid-based long-term energy storage. • Use of brownfield sites or existing land potential in commercial and industrial areas, excluding valuable soils or habitats. • The inclusion of logistics centres on the outskirts of the city can reduce intra-urban transport advantages. The results of this study show that Berlin can be self-sufficient in terms of aquaponic products. Taking realistic boundary conditions into account, a scenario was developed that envisages not only intra- but also peri-urban locations. The concepts of the productive city can offer opportunities for the implementation of urban aquaponics. The recommendations to policy makers are: • In the context of urban agriculture, aquaponics and trans-aquaponics should be a topic of Berlin's strategies and planning, with the aim of using circular economy resources in the city and making food production visible to citizens. • In the city-region, only aquaponics with integration of sustainable energy sources should be promoted. • Intra-urban space is prioritised. • Brownfield sites should be prioritised over unused commercial/industrial sites in the surrounding areas. • Freshwater fish should be preferred over meat in animal protein production. This should be taken into account in subsidies and propagated in public nutrition campaigns. • Simplification of the complex legal framework is needed. These political recommendations should be reflected in the planned Berlin Sustainability Strategy 2030. The range of methods developed in this work can also be applied to other urban regions, taking into account the concrete framework conditions.