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As we saw above, the design of successful aquaponic systems depends on the user group. High-yield, soil-less production requires a high input of technology (pumps, aerators, loggers) and knowledge, and is therefore mostly suited for commercial operations. However, it is entirely possible to design and operate low-tech aquaponic systems that require less skill to operate, and still yield respectable results. This implied trade-off (high-tech/low-tech) and the broad range of applications of aquaponics have consequences for further development pathways for the technology, system design, and socio-economic aspects. Aquaponic technology might develop in at least two directions: on the one hand towards low-tech solutions (probably mostly in developing countries and for non- professional applications) and, on the other hand, towards highly efficient hi-tech installations (predominantly in developed countries and with professional/commercial partners) (Junge et al. 2017).
While the technology itself does not pose limits to an area of the farm (because it can be modular), the size of urban farms is determined by (i) the characteristics of the available area, which is necessarily fragmented in a city (brownfield sites, underutilized or vacant buildings, and rooftops); and (ii) the constraints posed by the economics of crop production. As a rule of thumb, the area required to break even for commercial operations is around 1000 m2. Hobby and backyard installations can of course be much smaller. Aquaponic farms can grow/expand by increasing the number of operating systems (or modules), or by going vertical, although they cannot be scaled up too much without steeply increasing construction and energy costs. The size range of urban aquaponic farms will probably range between 150 m2 and 3000 m2, due to space, economic, and management limitations, but this could be enough to cover the basic requirements for an assortment of fresh vegetables for part of the urban population. Peri-urban aquaponic farms could be larger, and modified to include inland aquaculture systems or to re-use nutrient rich effluent or composted fish sludge in rural areas.
Aquaponic technology itself can be considered to be immature, since there are still problems to be solved. Simply linking a state-of-the-art aquaculture system with a state-of-the-art hydroponic system does not take into account other factors, such as problems with clogged drum filters, inefficient settlers, oxygen failures, poorly designed settlers, and clogged water pipes. Even though the influence of plant grow beds (NFT, drip irrigation, deep water culture) is already well known in hydroponic systems, the choice of those beds in aquaponic systems needs to be further studied since it will have consequences for productivity and operation. Further research is required in other areas as well. Since microorganisms are ubiquitous, they play an important part in all stages of aquaponic production. The influence of environmental conditions on their abundance, diversity, and roles could be investigated, for example by further use of Novel Generation of Sequencing methods (Schmautz et al. 2016a). One of the central questions is appropriate pest and disease control for aquaponics systems. Problems related to plant protection in aquaponics were discussed by Bittsanszky et al. (2016b). They concluded that since very few tools are available for plant protection in aquaponics, emphasis should be placed on precautionary measures to minimize the infiltration of pests and pathogens. On the other hand, the biological pest control methods currently available for organic agriculture have to be adapted to aquaponics (See Chapter 8).
If aquaponics is to be developed as a successful high-tech method of food production, one focus will need to be on reducing manpower requirements. While some automation is already well developed (for watering and feeding, online monitoring and alarms for many parameters, especially oxygen), it needs to be refined in order to allow for more precise and labour efficient operations, which will require the development of suitable sensors. One option to reduce manpower might be to use robots. Versatile systems, similar to FarmBot, should be developed for dedicated use in aquaponics.
While aquaponics has the potential to be sustainable, comprehensive life cycle analysis (LCA) studies of aquaponic operations and products are scarce (Forchino et al. 2017; Maucieri et al. 2018). However, it is clear that the ecological impact of aquaponics could be further improved by tapping into renewable sources of energy, developing daylight harvesting methods to avoid the use of electrical energy, using pre-treated or recycled water or rainwater, and improving the climate control of greenhouses. In an urban environment, aquaponics ought to be further integrated into buildings, allowing for gas, water and energy exchange between greenhouses and buildings. Improvements are also needed regarding organic material cycles. Fish feed is the main nutrient input and defines, to a large extent, the sustainability of the operation. Aquaponics (just like RAS) requires optimal nutrition for fish, and the fish feeds should consist of sustainable, locally sourced materials (organic, vegetarian, insects). The aquaponic loop should be further closed by digesting the fish sludge in order to re-use the nutrients in the aquaponic system, or by rearing redworms and/or insects on plant residues and using these for fish feed, with the residual fish sludge and plant waste being composted. The goal is to arrive at a zero-waste concept on the farm in order to reduce the carbon footprint. Studies on greenhouse gas emissions could make this picture complete. Finally, the possibility of using novel organisms in aquaponics (e.g. aquatic plants, marine fish, algae and seaweeds, crustaceans etc.) should be further explored in order to expand the ecological cycle. New aquaculture and plant products could also have implications for the economic viability of the technology, as the following section discusses.
Currently, aquaponics is a small but emerging business sector. Although food production is the basic goal of the operation, it is often combined with tourism and education in order to improve profitability. Because of its relatively novel technological cross-cutting approach, aquaponics has no clear legal status within the existing regulations in Europe (Joly et al. 2015). Whilst in the US aquaponic produce can be certified as organic, in Europe this is currently not possible because aquaponics involves soil-less plant production and RAS, both of which are not permitted by EU organic regulations.
Despite the potential of aquaponics as a food production technology, there are still open questions. As we have shown above, aquaponics is a prominent topic in the social media, but little is known about consumer knowledge and acceptance, which need be understood in different cultural and market settings. In general, we do not know enough about how the sustainability advantages of aquaponics should be communicated to consumers, compared to product quality such as taste, freshness, health, and price (Newman et al. 2014).
Until now, most research on aquaponics has focused on developing functional facilities. One way to improve profitability could be to improve efficiency. Efficient use of alternative energy sources, water, and the recycling of organic effluents will save on production costs, but they need to be evaluated against higher investment costs. To increase commercial production, novel business models must also be developed in relation to the emerging ideas of circular and local economies, yet managing interfaces increases complexity. Here, questions of framework conditions for operating costs, local logistics and determinants of vegetable and fish shopping behaviour will need to be addressed. Besides improvement in technological efficiency, there are also issues about operational management, and it could be interesting to explore new transport-sensitive varieties of crops in order to obtain a sufficiently high market price by avoiding competition with specialized horticulture. However, combining a new technology with new products also increases entrepreneurial uncertainty.
Aquaponics is especially useful for educators: even a small classroom system offers a wide range of possibilities for instruction at different educational levels, from primary school to university (see Chapter 15). Aquaponics can easily be integrated into all STEM (science, technology, engineering and mathematics) subjects, not only to demonstrate basic biological and ecological principles, but also chemistry, physics, and mathematics. A variety of competencies and skills can be gained by operating aquaponic systems, such as basic lab skills, team work, environmental ethics, to name but a few. The width of socio-economic aspects outlined here illustrates that aquaponics will only flourish with a broad collaboration between several additional key players beyond natural scientists and engineers. These could include, for example, (i) designers and architects to provide aesthetically pleasing designs; (ii) social scientists to help understand perceptions and acceptance of aquaponics among a wider audience; and (iii) health and nutritional scientists to explore how aquaponic products could be incorporated into diets as healthy and sustainably produced food. Feedback loops to system developers and plant and fish physiologists also need to be developed in order to improve systems with regard to consumer demand, sustainability, and the nutritional value of the products.
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