Module 1 Introduction

Physical System

Welcome to the course! As you progress through the modules, you will learn that aquaponics functions as a complex, integrated system. As you may have experienced before, studying topics with many interwoven relationships can be an overwhelming task. With this in mind, this course is structured in a fashion that breaks down the various components of an aquaponics system for individual examination. We will begin with the physical system, then water, then microbiology, then fish, followed by plants. Once you have had some time to learn about the individual system components, the course will then begin to integrate your understanding and look at the entire aquaponics ecosystem. An aquaponics system may be analogized by a system of carefully arranged dominoes, where every change you make has some effect on another component or aspect of the system. Once you develop knowledge about each element, you will be better prepared to examine the system as a whole. The course concludes with a holistic examination of aquaponics production.

The focus of Module 1 is the physical system. In this module, you will complete readings and exercises that will allow you to identify the various aquaponics growing techniques, understand their benefits and constraints, and identify the basic components and functions that make up aquaponic systems. You will also read about the operation and maintenance of functional aquaponic ecosystems. Your first module will conclude with a quiz to test your knowledge and comprehension, but do not worry, you will have a few practice questions along the way to see if you are on track.

Learning Outcomes

Upon completion of this module, you should be able to

1. Identify and recognize aquaponic grow methods
2. Identify and describe the function of the components that make up aquaponics systems
3. Identify and describe the pros and cons of different aquaponic growing techniques
4. Describe why to use one system over another
5. Identify the best grow methods for different conditions
6. Recognize the basic components required for a fully functioning aquaponics system

What is Aquaponics?

Operating as an integrated system, aquaponics combines the raising of fish (aquaculture) with the soil-less growing of plants (hydroponics). Aquaponics functions in a cycle in which, put simply, the fish provide nutrients for the plants and plants filter the water for the fish. The fish waste provides an organic food source for the growing plants and the plants provide a natural filter for the water the fish live in. The third component, but equally important and often forgotten participants, are the microbes (nitrifying bacteria and others). In some systems, there can be added components, such as in ebb and flow media-based systems, organisms such as red worms can be added to help decompose the organic wastes in the growing media. In essence, aquaponics utilizes the most effective components of aquaculture and hydroponics and reduces the drawbacks of each when they are done independently.

So why aquaponics? Aquaponics provides the ability to grow local, grow where there is no aerable land, grow where there is little water, and grow where there is little space. Aquaponics provides some clear advantages over soil-based production. For one, aquaponics uses little to no fertilizer—the water medium allows for more uniform concentrations, little biological transformation and ease of nutrient control. Second, aquaponics uses little water—an overall 90% reduction of water use verses conventional soil plant production. Essentially, percolation and runoff are non factors, so evaporation and transpiration account for all water loss from the system, which uses the same water over and over. Third, aquaponics supports monoculture—there is no need for crop cycling, enhancing organic matter or any of the other soil related factors to maintain productivity when you grow in aquaponics. Fourth, aquaponics requires less labour—there is no plowing, tilling, mulching, or weeding needed in aquaponics and harvesting is also simpler than in soil. Besides all of these benefits, aquaponics provides greater yields than hydroponics or soil. Why not aquaponics? Well, aquaponics is complex, and in order to be successful you need to learn the many interactive processes and become familiar with it as a system. Only once this familiarity happens will aquaponics become a simple and daily management routine.

An Overview of the Aquaponic System

As you have read, aquaponics essentially marries aquaculture and hydroponics. The integrated aquaponics system operates much like any general recirculation system; however, a critical component is the removal of solids. As stated by Rakocy, Masser, and Losordo (2006), there are five essential components of an aquaponics system:

• A fish rearing tank
• A settleable and suspended solids removal component (the clarifier)
• A biofilter
• A plant grow bed (hydroponic subsystem)
• A sump

Even though the system recirculates, let’s start our examination of its components at the fish rearing tank. The water quality in the fish rearing tank is closely monitored and maintained. In large part, what is fed and how much is fed to fish is important to maintain the desired water quality. From the fish tank, water and organic matter (e.g., solid fish waste) travel into a solids removal tank (a clarifier) that separates from the water the settleable and suspended solids through gravity or filtration. Next, the water passes through to the biofilter. The biofilter breaks down the ammonia (through nitrification). The water then moves into the plant grow bed (hydroponic sub system). This is where the plants reside and where they access the nutrient-rich water. Remember, there is no soil in an aquaponics system and the plant roots have direct access to the water. After nourishing the plants, the water collects in a reservoir (the sump) where it is pumped back to the fish rearing tank.

There are a variety of aquaponic system types and each type is a modification of this basic structure. However, the function(s) of each component of this basic structure remains consistent in each type of system. Later in this module, you will explore six system types: 1) deep flow technique (DFT), also known as deep water culture; 2) nutrient film technique (NFT); 3) ebb and flow, with or without media; 4) aeroponics; 5) drip; and 6) vertical.

Depending on the system type, the location of some components may vary. To illustrate, here is an example:

If elevated hydroponic troughs are used, the sump can be located after the biofilter and water would be pumped up to the troughs and returned by gravity to the fish-rearing tank… The biofilter and hydroponic components can be combined by using plant support media such as gravel or sand that also functions as a biofilter. Raft hydroponics, which consists of floating sheets of polystyrene and net pots for plant support, can also provide sufficient biofiltration if the plant production area is large enough. (Rakocy et al., 2006, p. 2)

Are you feeling confused? As you begin to study each system type, you will gain more clarity. As you move through this content, you will identify and describe the function of the components of each system, as well as the pros and cons of different aquaponic growing techniques. This material will allow you to describe why you would use one system over another.

Before we look at different system types, let’s explore solids and their role in aquaponics in more depth.

Removing Solids

The aquaponic system is highly influenced by the presence of suspended solids. Cumulatively, these are referred to as Total Suspended Solids (TSS) and will be further discussed in the module on water quality. Any time you are raising a live specimen, you will have to deal with fecal waste and uneaten food. The more of this matter that can be removed or retained from reaching the plant bed the better success you will have in aquaponics. Other suspended solids, such as organisms (e.g., bacteria, fungi, and algae), can also accumulate in the system and may cause disruption if present in large enough quantities. According to Rokacy et al. (2006), the role of suspended solids must be carefully considered.

Suspended solids entering the hydroponic component may accumulate on plant roots and create anaerobic zones that prevent nutrient uptake by active transport, a process that requires oxygen. However, some accumulation of solids may be beneficial. As solids are decomposed by microorganisms, inorganic nutrients essential to plant growth are released to the water, a process known as mineralization. Mineralization supplies several essential nutrients. Without sufficient solids for mineralization, more nutrient supplementation is required, which increases the operating expense and management complexity of the system. However, it may be possible to minimize or eliminate the need for nutrient supplementation if fish stocking and feeding rates are increased relative to plants. Another benefit of solids is that the microorganisms that decompose them are antagonistic to plant root pathogens and help maintain healthy root growth. (p. 4)

Note: In this course, as you examine visuals of each of the different aquaponics systems, you will see solids removal occurring in the clarifier.

This photograph of a DFT system shows the fish rearing tank in the back, the 
clarifier in the front left, and the biofilter to the right of the clarifier. 

Let’s look at an example of simple solids removal. Ebb and flow systems—which you will learn more about soon—may use media to secure the plants. The media act as the trap for suspended solids in aquaponic systems that utilize it in plant beds. The waste settles at the bottom of the media rather than around the plants. Remember, the presence of some solids is beneficial as it promotes mineralization. Sand and gravel in a system may increase the risk of clogs; as such, these media may need to be replaced from time to time, which is not an easy task. Using sand is becoming less popular, because sand has small interstitial spaces that easily clog. Small beads, extruded clay, or pea gravel allow for more effective flooding and drainage in an ebb and flow system. Note: a biofilter, if added to an aquaponics system, only functions to break down ammonia to nitrate (through nitrification); in other words, the biofilter does not break down solids, it is a chemical filter not a mechanical one.

There are a variety of devices that can be used to remove solids from intensive fish recirculation systems. They vary significantly in efficiency, solids retention time, effluent characteristics (both solid waste and treated water), and water consumption rate (Rakocy et al., 2006, p. 4). Devices include the following:

• Sedimentation devices/clarifiers (primarily remove settleable solids)
  • Settling basins
  • Tube or plate separators
  • A combination particle trap and sludge separator
  • Centrifugal separators
• Filtration devices (primarily remove settleable and suspended solids)
  • Microscreen filters
  • Bead filters

Which device for solid removal is appropriate for a given aquaponics system is dependent on “the organic loading rate (daily feed input and feces production) and secondarily on the plant growing area” (Rakocy et al., 2006, p. 5). So, if you have high organic loading—in other words, you are feeding a lot of fish who produce a lot of waste—relative to your plant growing area, you will need a high efficiency solids removal device. In this instance a microscreen drum filter may be best. “Microscreen drum filters capture fine organic particles, which are retained by the screen for only a few minutes before backwashing removes them from the system. In this system, the dissolved nutrients excreted directly by the fish or produced by mineralization of very fine particles and disolved in organic matter may be sufficient for the size of the plant growing area” (Rakocy et al., 2006, p. 5). In contrast, if you have low organic loading—in other words, you are feeding a small amount of fish who produce little waste—you may not even need to consider adding a solid removal device. In this case, more mineralization is necessary to meet the plants’ nutrient needs. You must consider this cautionary note however:

Unstablized solids (solids that have not undergone microbial decomposition) should not be allowed to accumulate on the tank bottom and form anaerobic zones. A reciprocating pea gravel filter (subject to flood and drain cycles), in which incoming water is spread evenly over the entire bed surface, may be the most appropriate device in this situation because solids are evenly distributed in the gravel and exposed to high oxygen levels (21 percent in air as compared to 0.0005 to 0.0007 percent in fish culture water) on the drain cycle. This enhances the microbial activity and increases the mineralization rate. (Rakocy et al., 2006, p. 5)

Note: Foam fractionators are sometimes used in systems to remove fine and dissolved solids. However, most aquaponic systems do not contain levels of fine and dissolved organic matter at a high enough level to require this addition.

On the following pages you will explore five specific aquaponic system types. As you read about each of these types, note how each system removes solids, as solids mishandling is one of the biggest causes of aquaponics failures.

Deep Flow Technique (DFT)

Deep Flow Technique (DFT) may also be referred to in literature as deep water culture or the raft method. In this system, the plants grow in net pots suspended in holes in a raft (usually made of polystyrene) and their roots grow directly into a bed of water. This water, of course, comes from the fish holding tank, but not before it passes through solids separation (in the clarifier) and the biofilter. Rafts can accommodate a variety of different plants as the holes can be spaced accordingly based on what you plan to grow. The root systems in a DFT system can be extensive. The plant growing tank in a DFT system is larger than most other system types in order to accommodate the raft(s). Plants can grow quickly in a DFT system. Rafts can be harvested of plants and replaced with seedlings to initiate a new growing cycle. With multiple rafts, you can have plants at various growing stages, which helps maintain the equilibrium of the system. DFT is a promising method for commercial operation.

The DFT system at Lethbridge College Aquaculture Centre for Excellence

Rakocy et al., (2006) discussion of an example DFT system, the UVI aquaponic system in St. Croix, Virgin Isl. in action:

A floating or raft hydroponic subsystem is ideal for the cultivation of leafy green and other types of vegetables. At the University of the Virgin Islands, the DFT system uses three sets of two raft hydroponic tanks that are 100 feet long by 4 feet wide by 16 inches deep and contain 12 inches of water. The channels are lined with low-density polyethylene liners (20 mil thick) and covered by expanded polystyrene sheets (rafts) that are 8 feet long by 4 feet wide by 1.5 inches thick. Net pots are placed in holes in the raft and just touch the water surface. Two-inch net pots are generally used for leafy green plants, while 3-inch net pots are used for larger plants such as tomatoes or okra. Holes of the same size are cut into the polystyrene sheet. A lip at the top of the net pot secures it and keeps it from falling through the hole into the water. Seedlings are nursed in a greenhouse and then placed into net pots. Their roots grow into the culture water while their canopy grows above the raft surface. The system provides maximum exposure of roots to the culture water and avoids clogging. The sheets shield the water from direct sunlight and maintain lower than ambient water temperature, which is a beneficial feature in tropical systems. A disruption in pumping does not affect the plant’s water supply as in gravel, sand and NFT systems. The sheets are easily moved along the channel to a harvesting point where they can be lifted out of the water and placed on supports at an elevation that is comfortable for workers. (p. 8)

Nutrient Film Technique (NFT)

NFT in Lethbridge College greenhouse.

(http://aquaponics-catfish.blogspot.ca/ (Links to an external site.))
An example of an NFT system.

The Nutrient Film Technique (NFT) system is commonly used in hydroponics, but it can also be used in aquaponics. In contrast to deep flow technique, in an NFT system, the plants grow in narrow channels with a continuous, thin stream of water. As such, there is a constant supply of new nutrients and greater oxygen from the fresh water flow. This system works best for plants with smaller roots as extensive root growth can cause clogging issues in an NFT system. Organic waste from the fish can also cause clogging in this type of system if it is not handled appropriately. An NFT system requires constant monitoring and maintenance. The slope of the plant troughs is critical to ensure proper water flow. Let’s look at a specific example of NFT as described by Rokacy et al., (2006):

NFT consists of many narrow, plastic troughs (4 to 6 inches wide) in which plant roots are exposed to a thin film of water that flows down the troughs, delivering water, nutrients and oxygen to the roots of the plants. The troughs are lightweight, inexpensive and versatile. Troughs can be mounted over rearing tanks to efficiently use vertical greenhouse space. However, this practice is discouraged if it interferes with fish and plant operations such as harvesting. High plant density can be maintained by adjusting the distance between troughs to provide optimum plant spacing during the growing cycle. In aquaponic systems that use NFT, solids must be removed so they do not accumulate and kill roots. With NFT, a disruption in water flow can lead quickly to wilting and death. Water is delivered at one end of the troughs by a PVC manifold with discharge holes above each trough; it is collected at the opposite, down-slope end in an open channel or large PVC pipe. The use of microtubes, which are used in commercial hydroponics, is not recommended because they will clog. The holes should be as large as practical to reduce cleaning frequency. (p. 8)

Ebb and Flow With or Without Media

The ebb and flow system may also be called a flood and drain system. This type of system may contain media (e.g., pea gravel, perlite) to support the plants or it may not; however, a system that does not have media is not common.

(Urban Vertical Farming Project (Links to an external site.))
Plants supported in media

In a basic ebb and flow system, the nutrient-rich water rises from a reservoir beneath the bed with the aid of a pump to flood the plants (with or without media). As in all other aquaponics systems the reservoir water is made nutrient-rich by the fish. The pump pushes the water up, usually on a timer through an inlet/outlet valve. The water rises to a predetermined height, flooding the roots with nutrient-rich water. Once the desired height is reached, the pump shuts off and water flows back down to the reservoir through the inlet/outlet valve. An overflow valve is situated just above the media (or desired water line in the plant bed).

Media

There are a variety of media available for use in the hydroponic subsystem. Let’s look at three common media.

• Gravel
• Expanded Clay
• Perlite

Gravel is commonly used as media in small hydroponic subsystems. “To ensure adequate aeration of plant roots, gravel beds have been operated in a reciprocating (ebb and flow) mode, where the beds are alternately flooded and drained, or in a non-flooded state, where culture water is applied continuously to the base of the individual plants through small diameter plastic tubing” (Rakocy et al., 2006, p. 7). Depending on the composition of the gravel, it may provide some nutrients to the plants; for example, “calcium is slowly released as the gravel reacts with acid produced during nitrification” (Rokacy et al., 2006, p. 7).

Gravel has some negative aspects, however. Due to its weight, strong support structures are necessary in your system. Suspended solids may also clog within the roots in the gravel, even after harvest. Reduced water circulation, increased microbial growth, and decomposition of organic matter can all lead to the formation of anaerobic zones, which smell bad and kill plant roots. Any plastic tubing used to irrigate gravel can also become clogged. The weight of gravel makes it difficult to move and maintain. It can also be challenging to plant in gravel. Gravel beds, because of their weight and clogging potential function best when kept small. Pea gravel may be a good alternative in an ebb and flow system with media. According to Rokacy et al. (2006):

One popular gravel-based aquaponic system uses pea gravel in small beds that are irrigated through a distribution system of PVC pipes over the gravel surface Numerous small holes in the pipes distribute culture water on the flood cycle. The beds are allowed to drain completely between flood cycles. Solids are not removed from the culture water and organic matter accumulates, but the beds are tilled between planting cycles so that some organic matter can be dislodged and discharged. (p. 7)

Aeroponic System

In an aeroponics system, the plants’ roots are not suspended in water, but rather, they hang in the air and are regularly misted with the nutrient-rich water from the fish rearing tank. The roots and the plant canopy are separated by the plant support structure. Aeroponics may also be called fogponics. The major advantage of aeroponics is that you can grow plants both horizontally or vertically (A-frame), which can save space and increase productive capacity if space is limited. Another big advantage is the ample supply of oxygen that the roots can get since they are exposed to the air. The nutrient rich water that is sprayed onto the plant roots is recollected into the circulation as it drips back down into the reservoir below. Regarding the drawbacks of this type of grow system, the water must be extra clean. No suspended solids can be present since spray heads will become clogged easily. Also, if the system goes down for some reason (e.g., power outage, leaks, pump goes down, etc.) the plants do not have much time before they begin to dry out and suffer.

Drip System

We will not spend a great deal of time examining the drip system; however, you should be aware that this is an effective option for commercial operations. The following images show a recirculation drip irrigation system that operates in Brooks, Alberta. As you can see in the images, the nutrient-rich water is dripped over the plants from a drip line. Just like in aeroponics, the water feeding the plants must be fine filtered of any suspended solids to avoid clogging the lines.

Tomatoes growing in a drip aquaponics system.

Cucumbers growing in a drip aquaponics system in the Crop Diversification Centre South (Alberta Agriculture).

Vertical System

Vertical systems are usually used in combination with different growing techniques; for example, areoponics, NFT, DFT, drip. The difference is that they are arranged vertically.

The following images show various vertical systems. Please keep in mind that in showing you these different systems, the course designers are not promoting any particular type of system; rather, the intent is for you to become aware that there are many different ideas out there. Each vertical system will have its pros and cons.

(https://zipgrow.ca/pages/zipfarm (Links to an external site.))
Bright AgroTech Zip Towers

(UniTan Aquafarms (Links to an external site.))
Vertical NFT system

(http://futuregrowing.com/info.html (Links to an external site.))
A vertical tower system which can be either a drip, NFT, or aeroponics type aquaponics systems or a combination. 

(http://www.pyramidgarden.com/photos (Links to an external site.))
Pyramid shape aeroponics system 

The Benefits and Limitations of Various Aquaponics Growing Techniques

Required Reading The following article provides information on the limitations and constraints of various aquaponic systems. Mann, T. (2015). What doesn’t work (Links to an external site.) This article compares three system types—DFT, NFT, media-based—providing you with additional information on each. Project Feed 1010, Institute for Systems Biology. (2014). Comparing the different methods of aquaponics growing (Links to an external site.)

System Type	Benefits	Limitations
Deep flow techniques	lots of room for root growth in the plant bed risk to plants reduced in case of pump failure can utilize a large bed to float and move plants for harvest	accumulation of solids in plant bed must be periodically cleaned size of the plant deeper & heavy water must be aerated/oxygenated
Nutrient flow techniques	constant introduction of new nutrients good oxygen supply to the roots can grow vertically	clogging potential high plant risk in case of pump failure works best with small root systems needs good temperature control
Ebb and Flow with media	media bed acts as the biofilter can grow a greater variety of plants good oxygen supply to the roots flexible plant spacing	media clogging potential size of plant bed deep & heavy high plant risk in case of siphon and/or pump failure
Ebb and flow without media	good oxygen supply to roots flexible plant spacing	size of plant bed deep algae growth in plant bed plants potted
Aeroponics	can grow vertically uses little water good oxygen supply to roots	clogging spray heads extra fine solids removal required high plant risk in case of pump and/or head failure
Drip	bed media acts a biofilter good oxygenation of roots good for deep rooting plants (e.g., cucumber, tomatoes) small grow bed	extra fine solids removal required drip line plugging
Vertical	increase production in space	labour and safety aspects increase when working at heights costs of artificial lighting (power, lights)

Construction Materials

As you have seen, an aquaponic system may be built from a variety of materials. Budget is usually a critical deciding factor for selecting materials. Sadly, this often leads people to inexpensive and questionable materials, which reduces the chances of their system being successful. Vinyl-lined, steel-walled swimming pools for example, are a poor choice. “Plasticizers used in vinyl manufacture are toxic to fish, so these liners must be washed thoroughly or aged with water for several weeks before fish can be added safely to a tank of clean water. After a few growing periods, vinyl liners shrink upon drying, become brittle and crack, while the steel walls gradually rust” (Rokacy et al., 2006, p. 9). Neoprene rubber liners are also not recommended as they are not impervious to chemicals and some fish (e.g., tilapia) can eat holes in them as they eat microorganisms. “If herbicides and soil sterilants are applied under or near rubber liners, these chemicals can diffuse into culture water, accumulate in fish tissue and kill hydroponic vegetables” (Rakocy et al., 2006, p. 9). If you are re-purposing a barrel or tank for aquaponics use, make sure you know what the tank was used for so that you aren’t leaching toxins from the tanks plastics into your system, another recipe for disaster, not to mention a health risk. Trace heavy metals may enter water from galvanized pipes (Zn), brass, bronze, or copper pipe (Cu) or aluminum and iron pipe (Al and Fe). Other trace toxins can leach from certain plastics (i.e., resins like lead arsenic from ABS piping).

Fiberglass tanks work the best for rearing tanks, sumps, and filter tanks as they are sturdy, durable, non-toxic, movable and easy to plumb. For fish rearing tanks and in gravel hydroponic subsystems, polyethylene is also popular as relatively inexpensive. Polyethylene is also an excellent construction material for troughs in NFT systems. This material is preferable to PVC piping as it is designed to prevent puddling and root stagnation (both of which can lead to root death). For floating hydroponic subsystems, expensive plastic options are available commercially. “A good alternative is the 20-mil polyethylene liners that are placed inside concrete block or poured-concrete side walls. They are easy to install, relatively inexpensive and durable, with an expected life of 12 to 15 years. A soil floor covered with fine sand will prevent sharp objects from puncturing the liners. Lined hydroponic tanks can be constructed to very large sizes—hundreds of feet long and up to 30 feet wide” (Rakocy et al., 2006, p. 9).