Aquaponics

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Aquaponics is the combination of aquaculture (fish farming) and hydroponics (growing plants using water rather than soil). It is an incredibly productive means of growing food, allowing a person to sustain themselves on less than 100m2. Some people with large systems growing 5000 plants a week have reported that, once their system is set up, they earn €1000 a week spending 2 hours a day at work. Aquaponics is ecologically sound and sustainable. Scalable designs for systems are available online.

See also:


Contents

[edit] How aquaponics works

Aquaponics.gif

Edible fish are grown in a tank. Their poop enriches the water with nutrients.
This enriched water is pumped into gravel beds with edible plants rooted in them. As the water flows through the gravel beds, the plants' roots and the bacteria that grow on the gravel take nutrients from the water. This both nourishes the plants and cleans the water.
The water, now clean, flows back into the fish tank.

The system provides fish, vegetables and herbs for people. Some systems have grown fruit trees aquaponically, but this is still experimental.

[edit] Feeding the fish

  • Commercially available fish food is the most common way of feeding the fish in aquaponics. The disadvantage is that your system then requires constant input of resources.
  • Algae will grow endemically in nearly any body of still water. Fish will eat these, but in practice it is not possible to grow enough algae to sustain an aquaponic system. You can increase the fraction of the fish's requirements met by algae by providing a surface underwater for the algae to grow on. (Remember when you had a goldfish as a kid, and the little castle in his tank got covered with green stuff?) Use something with high surface area.
  • Duckweed, an extremely fast-growing high-protein pond weed, can be grown on the surface of the tank. There are species of duckweed adapted to nearly all climates.
  • Insects. Herbs that attract insects can be grown in rafts on the surface of the fishtank. Mulberry and tea trees are used in aquaculture to attract insects as fish food.
  • Worms from a compost heap can be fed to the fish. The worms can be fed with grass cuttings, food waste and other organic waste. Some of the compost from the wormery can be added to the water input to the gravel beds; this diversifies the nutrients the plants receive. Aquaponics combined with vermiculture is nearly a closed-loop system. Organic waste is converted into worms, worms into fish, fish into vegetables. The fish and the vegetables are converted into human life!
  • Black Soldier Fly larvae. An integrated Black Soldier Fly and aquaponics system can turn 12kg of food waste into 1kg of delicious fish, plus the vegetables in the grow-beds.

Duckweed grows very fast and Black Soldier Fly larvae convert very efficiently. A system with a small duckweed tank, a wormery and a Black Soldier Fly bioconversion unit should have no problem getting by without buying fish food. This cuts operating costs to near zero. The more varied the fish's diet, the better they are likely to taste.

[edit] System design

A rule of thumb is that the volume of the gravel beds should be twice that of the fish tank. Gravel beds would typically be about 30cm deep.

Fish can normally be stocked at 2-3kg of fish per cubic meter of water.

The species of fish used depends on the climate.

[edit] Water quality

[edit] Temperature

The required temperature depends on the species of fish you want to grow. If you choose fish that are adapted to your local climate, you will save money on heating costs. Digital methods to measure temperatre, pH, dissolved oxygen, and possibly other parameters should be investigated as a way to gather information for system optimization, indications of system problems, and eventually labor savings.

[edit] pH

pH needs to be tested every week or more. A pH of around 6.2-6.4 is best, though this varies somewhat depending on the species of fish.

If pH gets too low, it could be a sign that parts of the gravel bed have developed anaerobic bacteria, which produce acids. If this happens, remove any plants with very large root systems, as these create pockets where air cannot get to.

If the pH is too high, it is generally a sign that the plant biofilters are not keeping up with the fish's production of ammonia. Plant more plants.

[edit] Oxygenation

Aquaponic systems require an air pump underwater. Having the flow from the gravel beds falling from a height and splashing into the fish tank will help oxygenate it too.

It is very important to keep the aerator pump running at all times. If the oxygen supply to the fish is cut off for just 45 minutes, you will have dead fish. For this reason, it is wise to have a backup air pump that will kick in if your pump fails. There can never be too much oxygen in the water; excess oxygen will bubble to the surface and escape.

[edit] Nutrients

A lot of aquaponic systems require calcium, potassium and iron to be added about every two weeks. If you have a wormery and add a little of the worm-compost to the water flowing into the gravel beds, this should provide these missing nutrients.

[edit] Open-source systems

[edit] Work to be done

Aquaponics is still in its infancy and is developing every year. More research needs to be done into polycultured systems that can grow more than one type of fish. (Different fish require different water temperatures and pH, so some species are incompatible. However, tilapia and prawns - which are both delicious - have been farmed together in fish farms [1].) Another avenue of research would be to use lights or herbs to attract insects to the tank where the fish can eat them; another step towards making a more diverse, more closed-loop system.

[edit] Concept for compost-heated, compost-powered aquaponic system

Say you want to set up an aquaponics system. You decide to grow tilapia, because they have many advantages for aquaponics. But tilapia like a water temperature of 28-30°C (82-86°F) and you live in a climate where it gets cold in winter. Using good greenhouse design, you are able to stabilize the temperature year-round, but there's no way you'll get it up to 28-30° without a heat source. This will require an input of power, in addition to the power needed for the pump.

There could be a way to kill two birds with one stone: build a thermophilic compost heap against one side of the fish tank. The heat from the compost will warm the water up. Care must be taken to keep the temperature of the greenhouse stable, as the pile can get up to 50°C (122°F). Secondly, for the pump you keep a stirling engine at the compost heap. This is driven by the heat of the composting and is hydraulically connected to the water pump. Just an idea...

[edit] Resources

  • Aquaponics System - An aquaponics enthusiast's website providing ideas and advice for setting aquaponics gardens.
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