System Layout #5 – Raft Aquaponics

Most commercial aquaponics units are raft systems.

This is largely due to the long standing influence of the UVI Aquaponics Research Center, and the success of their model.

Raft systems are somewhat under represented at the backyard level – particularly in Australia – probably due to early promotion of the Speraneo-style flood and drain model.

The Raft System

Raft aquaponics is essentially the same as the CHOP system but, instead of media-based flood and drain grow beds, raft tanks or troughs are used to grow plants.

The other essential difference is that raft systems invariably feature mechanical filtration.  Even aquaponics fundamentalists, who might argue (albeit unconvincingly) that particulate waste can remain in a flood and drain system, acknowledge the need for mechanical filtration in raft systems.

For practical purposes, water flows from the fish tanks through filters and into grow tanks or troughs which contain Styrofoam rafts.  The rafts support the plants.

The water flows from the grow tanks into a sump tank.  A pump located in the sump tank moves the water back to the fish tank.

The water in the raft system recirculates continuously.

The Aquaponics Research Centre located at the University of Virgin Islands (which has been operating for over 25 years) is arguably the most widely recognised aquaponics system in the world and serves as the model for most raft systems.

The advantages of the raft system include:

  • Its stability – the relative volume of water in a raft system ensures that it is more stable (in terms of water quality and temperature) than flood and drain systems of a comparable size.
  • Easier to operate – little testing required and minimal daily maintenance.
  • The existence of a large body of research data.
  • Cheaper to build than flood and drain systems of comparable size – small sump tank.
  • Higher productivity than flood and drain systems of a comparable growing surface area.
  • Portability – small backyard systems can be emptied and moved relatively easily.

Raft tanks can be built from timber, plywood, cement blocks, pre-cast concrete sections, fibreglass or (for smaller systems) plastic.

The plants are inserted into holes cut into the Styrofoam rafts.  The hole spacing will vary according to the type of plant to be grown.

Raft systems are ideal for the production of Asian greens, salad leaf vegetables and soft herbs, however, they have also been used to grow many other vegetables – particularly tomatoes.

It’s likely that raft aquaponics will become more common at the backyard level as people become better educated about its benefits.

-o0o-

Comments

  1. says

    I’m in the process of building a raft system in my backyard, using concrete blocks and pond liner. I’m planning to have a stair-step series of tanks that drain downward into the sump tank, and I’m trying to figure out where to get a mechanical clarifier like the one you pictured. Do people usually build them from scratch, or are there companies that sell them for this type of thing?
    Always inspired by what you do,

    -Mike

    • says

      Mike…..mechanical filters can take many forms. You can buy clarifiers or you can make them. If you send me a schematic of the layout of your proposed system, I can provide some ideas for where and how mechanical filtration can occur.

      Thank you for your kind words.

    • says

      Mike…….there’s no reason why your cascading arrangement won’t work…..just make sure that you can reach everything that you need to for planting, harvesting, maintenance, etc.

      You can make mechanical filters out of many things but they need to be relative to the size of the other components in the system.

      Mineralisation tanks can function in a variety of ways since their purpose is to assist the conversion of suspended solids into mineral elements that the plants can use. This can happen aerobically or anaerobically.

  2. Scott says

    I like this system. Can you place the sump tank (with pump)on top of the fish tank? Is there a way of seeing the different elevations of the components? I don’t know hydrology but there must be a certain way to go here.

  3. richard says

    I am starting to build 12 fish tanks in series, each 6.25 m long, 2m wide and 1.2 m deep, connected with two 3 inch poly pipe in walls tying tanks outer wall to building.
    So the building wall up to 1.2m is the inner fish tank wall.
    The idea started to cool air down before entering building louvres
    Then aquaponics was suggested, and beds are CHB 12 inch deep, built on top of rain water tanks, so height of 1.1 fish tank drains into 1m high veg beds, into 2 cu mtr sump, and returns back 17m into the start of the fish tanks, which surround building on 3 sides, at fountain head of 1.5 mtrs..
    I have a davey whisper 1000M 0.86 KW above ground swimming pool pump that has run 24/7 and dry sometimes when priming.
    I will also buy a similar size 3 speed pump for 50,000 gallons on slow speed, as it runs at 10% of the cost and 85% efficiency at slow speed, and add growing beds until the water flows round at normal speed.
    It is all head knowledge so far, so i will start off small with free tilapia fingerlings from municipality, and with 3 air pumps hope to keep them alive during brownouts.
    I have to feed 30 bible students to begin with, and also up to 200 Compassion families the church looks after.
    It is a labour of love in my retirement.

    My main questions are, can i do without mechanical filtration between last fish tank and first growing bed? I was thinking of using fine mesh to keep the tilapia fry out of the growing beds, and cleaning/replacing it daily.
    My other question is what is most economical pump, and what size, to buy. I calculate 50,000 gallons of fish tank, 80 mtrs long, into 60 sq mtrs of growing beds, into sump tank, then pumped 17 mtrs along ground, and lifted 1.5 mtrs into fountain above 1st fish tank.
    I would like plumbing to be similar to my Davey whisper 1000M Monarch 0.86 KW pump which i will use as back up in the event of pump failure.

    kind regards, richard.

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