Media Bed Aquaponic Unit - Step by Step Description

Summary

Aquaponics is the integration of recirculating aquaculture and hydroponics in one production system. The Media Bed or Ebb-Flow is the simplest of the three common methods of aquaponics being utilized at the present, mainly at the subsistence level. This technology provides a detailed explanation of the main components of this method and a step by step guide to construct a media bed unit.

Description

The media bed or ebb-flow aquaponic system consists of a grow bed with hydroponic media, such as expanded clay pebbles or gravel, and a fish tank area. The water is circulated from the fish tank to the grow bed where bacteria and plants remove the nutrients from the effluent. The cleaned water is thus returned to the fish tank and aerated. 

Components of the Media Bed Aquaponic Unit

In the media bed units, the medium is used to support the roots of the plants and also the same medium functions as a filter, both mechanical and biological. The main components of this unit are described in the following section.

1. Media Bed

Materials:

Media beds can be made from plastic, fibreglass or a wooden frame with water-tight rubber or polyethylene sheeting on the base and inside the walls. The most popular “do-it-yourself” (DIY) media beds are made from plastic containers, modified IBCs or even old bathtubs. It is possible to use all of the above as beds and other kinds of tanks so long as they meet these following requirements:

  • strong enough to hold water and growing media without breaking;
  • able to withstand difficult weather conditions;
  • made of food-grade material that is safe for the fish, plants and bacteria;
  • can be easily connected to other unit components through simple plumbing parts; and
  • can be placed in close proximity to the other unit components.

Shape:

The standard shape for media beds is a rectangle, with a width of about 1 m and a length of 1–3 m. Larger beds can be used or manufactured, but they require additional support (i.e. concrete blocks) in order to hold their weight. In addition, longer beds may have unequal distributions of solid wastes that tend to accumulate at the water inlet, raising the risk of anaerobic spots. The beds should not be so wide that the farmer/operator is unable to reach across, at least half-way.

Depth:

Media bed depth is important because it controls the amount of root space volume in the unit which determines the types of vegetables that can be grown. If growing large fruiting vegetables, such as tomatoes, okra or cabbage, the media bed should have a depth of 30 cm, without which the larger vegetables would not have sufficient root space, would experience root matting and nutrient deficiencies, and would probably topple.

2. Medium

The medium needs to have adequate surface area while remaining permeable for water and air, thus allowing the bacteria to grow, the water to flow and the plants roots to breathe. The medium must be inert, not dusty, and non-toxic, and it must have a neutral pH in order that do not affect the water quality. It is important to wash the medium thoroughly before placing it into the beds, particularly volcanic gravel which contains dust and tiny particles. These particles can clog the system and potentially harm the fishes’ gills. Finally, it is important to work with material that is comfortable for the farmer.

Several common media meeting these criteria are volcanic gravel (most used), light expanded clay aggregate, river-bed gravel, or pumice.

In addition, organic substrates such as coconut fibre, sawdust, peat moss or rice hull can be used. They are often inexpensive but risk becoming anoxic, deteriorating over time and clogging the system. However, organic substrate can be used for a time within aquaponics, and once it begins to deteriorate, the media can be removed from the system, composted, and used as a valuable soil addition for soil crops.

3. Filtration

The media beds serve as very efficient filters, both mechanical and biological. However, when media beds are improperly sized for the stocking density, it can become clogged with solids, leading to poor water circulation, anoxic areas and dangerous conditions. When this occurs, the medium needs to be washed, which is labour-intensive, disrupts the plant growing cycle and can briefly disturb the nitrifying bacteria. To avoid this situation be sure that the original design considered the stocking density, feeding regime, and used the feed rate ratio to calculate the required area of the media bed.

Alternatively, another solids capture device can be integrated into the unit design. This is also recommended where the stocking density exceeds 15 kg/m3 and/or if the feeding rate is above 50 g/day for each square metre of grow bed. There are several options for this additional mechanical filter. A rudimentary and cheap technique is to affix an old, orphan sock to the tap where water from the fish tank enters the media bed. This simple filter can be removed each day and rinsed. Another more elaborate method is to place a 3–5 litre bucket inside the media bed with several small holes (6–8 mm) drilled into the side surfaces. Sponges, nylon netting or even growing media (volcanic gravel, LECA) can be tied in a porous inert net bag and placed into this bucket. This filter will trap the solid waste, and the filter can then be removed periodically to be rinsed and replaced.

4. Three zones of media beds

The nature of a flood-and-drain media bed creates three separate zones that can be considered micro-ecosystems, which are differentiated by their water and oxygen content. Each zone hosts a diverse group of bacteria, fungi, micro-organisms, worms, insects and crustaceans. One of the most important is the nitrifying bacteria used for biofiltration, but there are many other species that all have a role in the breaking down of fish wastes.

5. Irrigation system

There are different techniques to deliver water to media beds, each can be relevant depending on the local availability of materials, the degree of technology desired or the experience of the operators. Water can be simply trickled from holed pipes uniformly distributed on the medium; this is a perfectly acceptable design.

A method called flood-and-drain, also known as ebb-and-flow, can be used where the system of plumbing causes the media beds to flood with water from the fish tank and then drain back in the sump tank. This is accomplished through autosiphons or timed pumping. This alternation between flooding and draining ensures that the plants have both fresh nutrients and adequate air flow in the root zone. This thereby replenishes the oxygen levels for plants and bacteria. It also ensures that enough moisture is in the bed at all times so the bacteria can thrive in their optimum conditions.

A flood-and-drain design using bell autosiphons is described in the following section.

Step by Step guide to construct a media bed unit

Materials: A detailed list of materials and tools needed for the construction of a media bed unit is attached at the bottom of this section (please see further reading, page 217)

1. Preparing the fish tank

Remove the two horizontal steel lengths attached to the top surface of the IBC tank holding the inner plastic container in place. The steel lengths are fixed with 4 star headed screws. Remove these four screws (Figure 1) using a star headed screwdriver (Figure 2) or star-headed key (Figure 3). Once the steel lengths are removed, pull out the inner plastic tank. If there is no star key, cut the screws with an angle grinder.

 

After pulling out the tank, draw a rough square shape on the top surface of the tank 5 cm from the 4 sides of the tank (Figure 4). Then, using the angle grinder (Figure 5), cut along the square shape and remove the cut piece from the top (Figure 6). Once removed, wash the inside of the container thoroughly with soap and warm water and leave to dry for 24 hours (Figure 7). The cut piece removed can be used as the fish tank cover.

2. Installing the fish tank pipe

On one side of the IBC tank, mark a point 12 cm from the top and 12 cm from the side of the tank (Figure 8), and drill a hole at that point using the 57 mm circular drill bit (Figure 9). Insert a 50 mm uniseal (Figure 10) inside this hole. Attention: the circular drill bit size should be 57 mm and not 50 mm (see Figure 8).

The fish tank exit pipe is made of 2 lengths of PVC pipe (50 mm) combined using a PVC elbow (50 mm) and PVC coupler/straight connector (50 mm) (Figure 11). The length of PVC (50 mm) along the bottom surface of the tank is cut with horizontal slits 23 mm wide by using the angle grinder (Figure 12) to allow solid waste to enter the pipe but to prevent fish from doing so. The open end of the PVC length along the bottom surface of the fish tank is sealed with a PVC endcap/stopper (50 mm). Slot a short length of PVC (50 mm) through the uniseal (50 mm) and attach to a PVC elbow (50 mm) on the inside end (Figure 11) and then attach the other (vertical) pipe length to the elbow that is now connected to the uniseal (50 mm). Finally, drill a 2–3 cm diameter hole into the PVC elbow (50 mm) attached to the uniseal (50 mm) (Figure 13). This small hole prevents any air seal forming inside the pipe, which would drain all the water out of the fish tank in the event of power cut or if the pump stopped working. This is also called an accidental siphon. This step is not optional.

3. Preparing the media beds and sump tank

To make the 3 media beds and 1 sump tank, the 2 other IBC tanks are needed: the first to make the sump tank and 1 media bed, and the second to make the two remaining media beds. Take the 2 IBC tanks and remove the 4 steel profiles and pull out the plastic containers as shown before in Figures 1–3.

4. Making two media beds from one IBC

First, stand the plastic inner container upright (Figure 14) and mark, using a metre stick and pencil, two bisecting lines 30 cm from both sides of the tank (as seen in Figure 15). Make sure to mark the exact lines (shown in the Figure 15). Take the angle grinder and carefully cut along both bisecting lines marked out to create two uniform containers with a depth of 30 cm (Figure 16). Then, take both containers and wash them thoroughly using natural soap and warm water and leave them out to dry in the sun for 24 hours.

5. Metal support for the media beds

Take the IBC metal support frame and cut out two support frames by following the same bisecting lines shown in Figure 14 using the angle grinder (Figure 17). When cutting the two 30 cm sides of the support frame, make sure to keep the two horizontal steel profiles intact as they will provide excellent support to the sides of the beds once they are full of water and medium (Figure 18).

Then, take both support frames and lay them out on the floor. Take the wood lengths (4 lengths of 104 cm, 1 length of 42 cm and 1 length of 48 cm) and place them on top of the support frame as shown in Figure 19. These wood lengths keep the media bed horizontal, which is vital for the functioning of the bell siphons. Next, take the washed media beds and place them on top of the support frame and wood lengths (Figure 20). Finally, slot in the remaining wood lengths in between the plastic media bed and support frame on both sides of each bed to provide further support (Figure 21).

6.  Making a sump tank and one media bed from an IBC

Take the remaining IBC, place it upright and mark out, using a metre stick and pencil, only one 30 cm bisecting line as seen in Figure 22. Then, take the angle grinder and cut the inner plastic container and metal support frame at once by following the bisecting line (see Figure 22). Remove the 30 cm container (third media bed) from the remaining 70 cm container (sump tank) (Figure 23). Wash out both containers thoroughly with natural soap and warm water and leave in the sun for 24 hours.

For the third media bed, follow the same steps regarding the wood lengths as detailed above for the first two. Finally, take the sump tank container and drill two holes (25 mm diameter) using the conical drill bit as shown in (Figure 25) (25 mm pipes will be inserted into both of these holes later, the pipes will drain water from each media bed).

7.  Preparing the bell siphons

The following materials are needed to make one siphon, so 3 of each are needed in total:

  • 35 cm media guard (110 mm PVC pipe)
  • 27 cm bell [PVC pipe (75 mm) with flaired end + endcap/stopper (75 mm) + rubber washer (75 mm)]
  • 16 cm standpipe (25 mm PVC pipe)
  • Barrel connector (25 mm)
  • PVC reducer (40–25 mm)
  • PVC female adaptor (25 mm × 1 inch)
  • PVC elbow (25 mm × 1 inch female)

First, create the bell. Take a 27 cm section of PVC (75 mm) and cut out 2 pieces as shown in Figure 26 using the angle grinder. Then, drill a hole (10 mm in diameter) using a drill bit about 1.5 cm from the two cut pieces as shown in Figure 26. Finally, seal one end of the bell using the PVC endcap/stopper (75 mm) and rubber washer (75 mm). Next, make the media guards from the 35 cm length of PVC pipe (110 mm) and cut 5 mm slots along their entire length using the angle grinder (Figure 27). Now, take each media bed and mark their centre points in-between the two wooden lengths below as shown in Figure 28. Drill a hole (25 mm in diameter) at each centre point (Figure 29) and insert the barrel connector (25 mm) with the rubber washer placed inside the media bed. Tighten both sides of the barrel connector using a wrench (Figure 30).

Screw the PVC adaptor (1 inch – 25 mm) onto the barrel connector (25 mm) inside the media bed and then slot the standpipe into the PVC adaptor (1 inch – 25 mm). After, attach the second PVC adaptor (25–40 mm) to the top of the standpipe (Figures 31–33). The purpose of this adapter is to allow a larger volume of water to initially flow down the standpipe when the water has reached the top. This helps the siphon mechanism to begin draining the water out into the sump tank.

Place the bell siphons and the media guards over the standpipes (Figures 34–36).

Finally, connect the PVC elbow (1 inch–25 mm) to the other end of the barrel connector underneath the media bed, which allows the water to flow out of the media bed (Figures 37–39).

8.  Assembling the media beds and sump tank

First, place the sump tank and brace it with six concrete blocks from each side (12 blocks in total) as shown in Figures 40 and 41. Make sure the blocks do not cover the holes already drilled into the sump tank (Figure 42).

Place the remaining blocks and the fish tank according to the distances described in Figure 43. The fish tank should be raised up about 15 cm from the ground. This can be done by using concrete blocks as shown in Figure 43. Place the three media beds (including the metal support frames and wood lengths) on top of the blocks (as shown in Figure 44). Make sure the grow beds are secured on top of the blocks and horizontal by verifying with a spirit level. If not, slightly adjust the layout of the blocks underneath.

9. Plumbing the unit: fish tank to the media beds (distribution manifold)

The plumbing parts needed for this section are as follows:

  • Barrel connector, B-type (1 inch) × 3
  • PVC tap (1 inch) × 3
  • PVC endcap/stopper (50 mm) × 3
  • PVC elbow (50 mm) × 2
  • PVC connector, T (50 mm) × 2
  • PVC coupler (50 mm) × 3
  • 150 cm of PVC pipe (50 mm) × 1
  • 85 cm of PVC pipe (50 mm) × 1

Go back to the “preparing the fish tank” (2.2) instructions. The last instruction shows a length of PVC (50 mm) slotted through the uniseal (50 mm) and exiting the fish tank. Take another PVC elbow (50 mm) and connect it to the pipe slotted through the uniseal (Figure 45). Then, using a PVC straight coupler (50 mm) and another PVC elbow (50 mm), connect the fish exit pipe to the distribution pipe (50 mm) at the same height as the top of the media bed (Figure 46).

On each media bed, a valve is used to control the water flow entering the bed. To include a valve, first take a PVC endcap/stopper (50 mm) and drill a hole (25 mm diameter). Insert a barrel connector (25 mm) into the hole and tighten both ends using a wrench. Then, wrap Teflon tape around the threads of the male end of the barrel connector and screw the tap valve (1 inch) onto the barrel connector (Figures 47–50).There is one valve for each media bed for a total of three valves.

From the PVC elbow (50 mm) attached to the fish exit pipe, follow the pipe layout shown in Figure 51 that allows water to flow into each media bed. Materials include: PVC pipe (50 mm), PVC elbow (50 mm) and PVC T-connector (50 mm). Next, attach the pipe caps fitted with the valves to the PVC T connectors and PVC elbow connectors from the distribution pipe as in Figure 51, using one for each media bed. Use a PVC straight coupler (50 mm) if necessary.

10. Plumbing the unit: media beds to the sump tank (drain pipe)

Figures 52 and 53 show the media beds marked as A, B and C. For media bed A, attach a drain pipe of 60 cm length of PVC pipe (25 mm) to the elbow connection underneath the media bed (Figure 54), which exits from the bottom of the bell siphon standpipe. Next, slot the 60 cm length of pipe into the closest drilled hole on the side of the sump tank allowing the water to flow directly into the sump. Attaching media beds B and C (Figure 53): Under media bed C attach a PVC elbow connector (25 mm to 1 inch) to the end of the barrel connector (Figure 54). Then, take a 2 metre length of polyethylene pipe (25 mm) and attach it to the drilled holes at the side of the sump tank (Figures 53 and 55). Do the same with media bed B using 1 metre of polyethylene pipe (25 mm) (Figure 55). Now, the water exiting media beds B and C will flow through separate polyethylene pipes (25 mm) into the sump tank.

Finally, it is advisable to fix the pipes underneath the beds to the metal frame using cable ties to relieve any pressure on the pipe fittings (Figure 54).

11.  Plumbing the unit: sump tank to the fish tank

Take the submersible pump and attach a polyethylene pipe (25 mm) using a PVC straight connector (1 inch – 25 mm), or any other connector that can attach the specific pump to the 25 mm pipe (Figure 56). Take a length of the polyethylene pipe (25 mm) that is long enough to reach the inside of the fish tank from the submersible pump (Figure 57). Attach one end to the submersible pump and the other into the top of the fish tank (see Figure 57–60). It is recommended to use the fewest connectors, especially elbows, between the pump and fish tank which will decrease pumping capacity. Place the electric box in a safe place higher than the water level and shaded from direct sunlight. Make sure it is still waterproof after plugging in the water and air pump plugs (Figure 61).

12. Adding the medium and running the unit

All parts of the system are now in place except for the growing medium (volcanic gravel) in the beds. Yet before the media is added, it is recommended to fill the fish tank and sump tank with water and run the pump to check for any leaks in the system. While checking for leaks, remove the standpipe and bell siphon so the water flows straight into the sump tank. If leaks appear, fix them immediately where they arise by tightening the plumbing connections, re-applying Teflon to the treaded connections and making sure all taps are in their ideal position (Figures 62–67). Once all the leaks are fixed and the water is flowing smoothly through all components of the unit, re-assemble the siphon bell and standpipes fill the beds with medium to a depth of 30 cm (Figures 68 and 69).

 

This technology comes along with other practices about Aquaponic unit:

1.   Designing an Aquaponic unit

2.   Media Bed Aquaponic Unit - Step by Step Description

3.   Nutrient Film Aquaponic Unit – Step by Step Description

4.   Deep Water Culture Aquaponic Unit – Step by Step Description

5.   Management of the Aquaponic Systems

 

Further reading

Small-scale aquaponic food production - Integrated fish and plant farming (FAO, 2014): http://www.fao.org/3/a-i4021e/

7 rules-of-thumb to follow in aquaponics: http://www.fao.org/zhc/detail-events/en/c/320156/

Created date

Wed, 03/06/2015 - 16:21

Source(s)

Fisheries and Aquaculture Department (FI) in FAO

Fisheries and aquaculture have the capacity – if supported and developed in a regulated and environmentally sensitive manner – to contribute significantly to improving the well-being of poor and disadvantaged communities in developing countries and to achievement of several of the Millennium Development Goals, especially those related to poverty reduction and food and nutrition security, environmental protection and biodiversity. As part of a long-term strategy, the FAO Fisheries and Aquaculture Department (FI) is envisioning a world in which responsible and sustainable use of fisheries and aquaculture resources makes an appreciable contribution to human well-being, food security and poverty alleviation. In this regard, FI works towards strengthening global governance and the managerial and technical capacities of members and to lead consensus-building towards improved conservation and utilization of aquatic resources. The activities of FI reflect the main FAO mandate of managing knowledge and information, assuring a global neutral forum for Members and providing technical assistance at national, regional and global levels.

In addition, the FAO Fisheries and Aquaculture Department undertakes capacity development activities for marine and inland fisheries as well as aquaculture. These include training at different levels, preparation of training and extension materials for general or targeted training, awareness raising through workshops, and collaboration with partner training institutions.  The FI is also involved in the development of appropriate technical guidelines and the promotion of participatory approaches in sustainable and responsible aquatic resources management, including gender aspects.

The Aquaculture Branch of FI (FIAA) is particularly responsible for providing technical assistance towards sustainable and responsible aquaculture development and management in support of improving food and nutrition security and alleviating poverty, globally.

The Products, Trade and Marketing Branch (FIAM) of the Fisheries and Aquaculture Department of FAO, assists FAO member countries on all aspects related to post-harvest. FIAM provides technical assistance in areas such as marketing, trade, handling and processing and preservation of fish products, food safety and nutrition. As such, FIAM supports activities along the value chain aiming at a sustainable supply of fish and fishery products in the market, while securing greater benefits for actors in the value chain. FIAM has broad experience in the field of promotion fish consumption, through the dissemination of knowledge on the nutritional value of fish and fishery products, including the promotion of good hygienic practices at any level of the supply chain (on board canoes/vessels, landing sites, aquaculture farms, factories and sales points).  Local fishermen and processors are assisted to adapt best practices in order to reduce food losses and waste, and to promote an optimal use of their fishery by-products, improving their returns, minimizing the environmental impacts and contributing to food security. Finally, as fish and fishery products are among the most traded food commodities worldwide, FIAM coordinates the implementation of Globefish, a programme collecting and disseminating information on markets and fish trade. Globefish produces a number of publications including fish price reports (European Fish Price Report), market studies (GLOBEFISH Research Programme) and trend analysis (GLOBEFISH Highlights).

 

Contacts: 
Contact person: 
Aquaculture Branch of the Fisheries and Aquaculture Policy and Resource Division
Contact email: 
Contact person: 
Alessandro Lovatelli (Aquaculture Branch)
Contact person: 
Aina Randrianantoandro (Products, Trade and Marketing Branch)
Country: 
Italy