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This chapter discusses the theory and design of aquaponic systems. There are many design aspects to take into consideration, as virtually all environmental and biological factors will have an impact on the aquaponic ecosystem. The aim of this chapter is to present these aspects in the most accessible way and to provide a thorough explanation of each component within an aquaponic unit.
Section 4.1 discusses the factors to consider when selecting a site for an aquaponic unit, including access to sunlight, wind and rain exposure, average temperature and others. Section 4.2 discusses the general aquaponic components essential for any method of aquaponics, including the fish tank, water and air pumps, the biofilter, the plant growing method and associated plumbing materials. The hydroponic component is then discussed in further detail, focusing on the three most common methods used in aquaponics: the media bed method (Figures 4.1-4.5); the nutrient film technique (NFT) method (Figures 4.6-4.9); and the deep water culture (DWC) method (Figures 4.10-4.13).
|Method||Abbreviation||Other names||Name of planting area||Section|
|Deep water culture||DWC||floating raft||canal, trough||4.3|
|Nutrient film technique||NFT||pipe, gutter||4.4|
|Media bed||n/a||particulate||bed, tray||4.5|
A specific section then presents a particular type of DWC with low stocking density. A final summary table of each method is provided in order to compare and contrast these three methods.
This chapter is intended only to explain the essential unit components and different methods of aquaponics. For more information regarding the sizing and design ratios for different unit components, please see Chapter 8, which provides the more detailed information, figures and design plans needed to actually design and construct small- scale aquaponic units. In addition, Appendix 8 gives a full step-by-step guide to building a small-scale version of the three methods explained in this chapter using materials widely available.
The main factors when deciding where to place a unit are: stability of ground; access to sunlight and shading; exposure to wind and rain; availability of utilities; and availability of a greenhouse or shading structure.
There are three main types of aquaponics: the media bed method, also known as particulate bed; the nutrient film technique (NFT) method; and the deep water culture (DWC) method, also known as the raft method or floating system.
The essential components for all aquaponic units are: the fish tank, the mechanical and biological filtration, the plant growing units (media beds, NFT pipes or DWC canals), and the water/air pumps.
The media beds must: (i) be made of strong inert material; (ii) have a depth of about 30 cm; (iii) be filled with media containing a high surface area; (iv) provide adequate mechanical and biological filtration; (v) provide separate zones for different organisms to grow; and (vi) be sufficiently wetted through flood-and- drain or other irrigation techniques to ensure good filtration.
For NFT and DWC units, mechanical and biofiltration components are necessary in order to respectively remove the suspended solids and oxidize the dissolved wastes (ammonia to nitrate).
For NFT units, the flow rate for each grow pipe should be 1-2 litres/minute to ensure good plant growth.
For DWC units each canal should have a retention time of 2-4 hours.
High DO concentration is essential to secure good fish, plant and bacteria growth. In the fish tank DO is supplied by means of air stones. Media bed units have an interface between the wet zone and dry zone that provides a high availability of atmospheric oxygen. In NFT units, additional aeration is provided into the biofilter, while in DWC air stones are positioned in both biofilter and plant canals.
Source: Food and Agriculture Organization of the United Nations, 2014, Christopher Somerville, Moti Cohen, Edoardo Pantanella, Austin Stankus and Alessandro Lovatelli, Small-scale aquaponic food production, http://www.fao.org/3/a-i4021e.pdf. Reproduced with permission.