Chapter 7 Coupled Aquaponics Systems
7.9 Some Advantages and Disadvantages of Coupled Aquaponics
The following discussion reveals a number of key pros and challenges of coupled aquaponics as follows: Pro: Coupled aquaponic systems have many food production benefits, especially saving resources under different production scales and over a wide range of geographical regions. The main purpose of this production principle is the most efficient and sustainable use of scarce resources such as feed, water, phosphorous as a limited plant nutrient and energy. Whilst, aquaculture and hydroponics (as stand-alone), in comparison to aquaponics are more competitive, coupled aquaponics may have the edge in terms of sustainability and thus a justification of these systems especially when seen in the context of, for example, climate change, diminishing resources, scenarios that might change our vision of sustainable agriculture in future.
· Aquaponics Food Production Systems7.8 System Planning and Management Issues
Coupled aquaponics depends on the nutrients that are provided from the fish units, either a commercial intensive RAS or tanks stocked under extensive conditions in smaller operations. The fish density in the latter is often about 15—20 kg/msup3/sup (tilapia, carp), but extensive African catfish production can be higher up to 50 kg/msup3/sup. Such different stocking densities have a significant influence on nutrient fluxes and nutrient availability for the plants, the requirement of water quality control and adjustment as well as appropriate management practices.
· Aquaponics Food Production Systems7.7 Fish and Plant Choices
7.7.1 Fish Production In larger scale commercial aquaponics fish and plant production need to meet market demands. Fish production allows species variation, according to the respective system design and local markets. Fish choice also depends on their impact onto the system. Problematic coupled aquaponics fish production due to inadequate nutrient concentrations, negatively affecting fish health, can be avoided. If coupled aquaponic systems have balanced fish to plant ratios, toxic nutrients will be absorbed by the plants that are cleaning the water.
· Aquaponics Food Production Systems7.6 Saline/Brackish Water Aquaponics
A relatively new field of research is the evaluation of different salinities of the process water for plant growth. Since freshwater worldwide is in continuously increasing demand and at high prices, some attention has been given to the use of saline/brackish water resources for agriculture, aquaculture and also aquaponics. The use of brackish water is significant as many countries such as Israel have underground brackish water resources, and more than half the world’s underground water is saline.
· Aquaponics Food Production Systems7.5 Scaling Coupled Aquaponic Systems
Typical coupled aquaponic system range from small to medium scale and larger sized systems (Palm et al. 2018). Upscaling remains one of the future challenges because it requires careful testing of the possible fish and plant combinations. Optimal unit sizes can be repeated to form multiunit systems, independent of the scale of production. According to Palm et al. (2018), the range of aquaponic systems were categorized into (1) mini, (2) hobby, (3) domestic and backyard, (4) small/ semi-commercial and (5) large(r)-scale systems, as described below:
· Aquaponics Food Production Systems7.4 Aquaculture Unit
The fish-rearing tanks (size, numbers and design) are selected depending on the scale of production and fish species in use. Rakocy et al. (2006) used four large fishrearing tanks for the commercial production of O. niloticus in the UVI aquaponic system (USA). With the production of omnivorous or piscivorous fish species, such as C. gariepinus, several tanks should be used due to the sorting of the size classes and staggered production (Palm et al.
· Aquaponics Food Production Systems7.3 Coupled Aquaponics: General System Design
The coupled aquaponics principle combines three classes of organisms: (1) aquatic organisms, (2) bacteria and (3) plants that benefit from each other in a closed recirculated water body. The water serves as a medium of nutrient transport, mainly from dissolved fish waste, which is converted into nutrients for plant growth by bacteria. These bacteria (e.g. Nitrosomonas spec., Nitrobacter spec.) oxidize ammonium to nitrite and finally to nitrate. Therefore, it is necessary for the bacteria to receive substantial amounts of ammonium and nitrite to stabilize colony growth and the quantity of nitrate production.
· Aquaponics Food Production Systems7.2 Historical Development of Coupled Aquaponics
Most original research efforts on coupled aquaponic systems took place in the USA with an increasing presence in the EU partly initiated by COST Action FA1305, The EU Aquaponics Hub and in other European research centres. Nowadays, fully recirculating aquaponic system designs almost completely dominate the American aquaponics industry, with estimates that over 90% of the existing aquaponic systems in the USA are of a fully recirculating design (Lennard, pers. comm.
· Aquaponics Food Production Systems7.1 Introduction
Fig. 7.1 Diagram of the first system by Naegel (1977) growing Tilapia and common carp in combination with lettuce and tomatoes in a closed recirculation system The combination of fish and plant cultivation in coupled aquaponics dates back to the first design by Naegel (1977) in Germany, using a 2000 L hobby scale system (Fig. 7.1) located in a controlled environment greenhouse. This system was developed in order to verify the use of nutrients from fish waste water under fully controlled water recirculating conditions intended for plant production including a dual sludge system (aerobic/anaerobic wastewater treatment).
· Aquaponics Food Production Systems