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The ‘hardware’ of an aquaponic system consists of (i) the fish tank, (ii) the water and air pumps, (iii) the solids removal units (drum filters, settlers), (iv) the biofilter, (v) the plant grow beds, and (vi) the plumbing materials. These elements are populated by a community, where the primary producers (plants) are separated from consumers (mostly fishes), and ubiquitous microorganisms build a ‘bridge’ between the two main groups.
Figure 2: Main components of an aquaponic system (redrawn after Rakocy et al. 2006)
Aquaculture is the captive rearing and production of fish and other aquatic animal and plant species under controlled conditions (Somerville et al. 2014). Aquaculture is becoming an increasingly important source of global protein production, while decreasing the pressure on the overfished oceans. However, aquaculture techniques such as open-water systems, pond cultures, and flow- through systems, all release nutrient-rich wastewater into the environment, causing eutrophication and hypoxia in the water bodies. In recirculating aquaculture systems (RAS) this waste water is treated and re-used within the system. However, these systems consume much energy and generate a lot of fish sludge which has to be treated separately. Thus, aquaponics can also be viewed as a form of RAS, or an extension of RAS.
Figure 3: The main types of aquaculture systems. For details see Chapter 2
The development of hydroponics can be traced back to the work by Dr William Gericke at the University of California in 1929 (Gericke 1937). Hydroponics has been expanding in the last decades, primarily because it allows increased yields by reducing pests and soil-borne diseases, and by manipulating growing conditions to meet optimal plant requirements, while increasing water- and fertilizer-use efficiency. It also allows for the development of agriculture on poor-quality land (Somerville et al. 2014). However, so-called conventional hydroponic cultivation also has its drawbacks. It utilizes costly, and often unsustainably sourced, mineral fertilizers to produce crops, and it consumes energy. Hydroponic systems require a considerable amount of macronutrients (C, H, O, N, P, K, Ca, S, Mg) and micronutrients (Fe, Cl, Mn, B, Zn, Cu, Mo, Ni), which are essential for the growth of plants. The nutrients are added to hydroponic solutions in ionic form, while C, H and O are available from air and water. The concentrations of nutrients need to be monitored. Aquaponic systems, on the other hand, use water that is rich in fish waste as the source of nutrients for plant growth. However, the nutrient composition of the water is not always perfectly matched to the plants' requirements. Some nutrients are often deficient, so they need to be added to adjust their concentration, for example iron, phosphate, and potassium (Bittsanszky et al. 2016a). Chapters 5 and 6 explain more about nutrients.
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