Aquaponics Combines Fish and Plants

September 15, 2016

in Food

Hydroponics is a way of growing plants without dirt. The plants are supplied their needed nutrients through a flow of either water alone or water and some form of growing medium, such as rocks or vermiculite. Aquaponics builds upon this idea and adds fish into a closed loop growing environment. Food for the fish is added to the water. The fish eat the food and excrete waste into the water. The plants absorb the fish waste products from the water as their nutrients and in the process, purify the water that the fish need. The water is pumped around in a circle from fish to plants and back again.

There is a large range of design and configuration concepts available for aquaponics. Simple at home systems can start with an aquarium for fish and floating plants. A design called “barrel-ponics” uses 55 gal rain barrels cut in half, with one half used for fish and the other half containing growth media and plants. A similar but larger design uses Intermediate Bulk Containers (aka IBC totes) also cut to make a large fish tank and a smaller growing bed. Large designs can go up to swimming pool sized fish tanks. Commercial designs have no size limit. All of these systems need water pumps and plumbing, some require airation and some use extra filtering techniques (such as swirl tanks to collect sediments).

Plant growing beds hydroponic systems take many shapes but most are some form of rectangular beds that can hold a growth medium and can be flooded with the water bringing the nutrients. They can also take vertical forms, where drip feeds supply the plant roots, often inside PVC pipes. The form is not important, but the function of being flooded or in some way supplying the nutrient water is important. The growth bed also needs to supply drainage and circulation.

The simplest plumbing is just to pump the water from the fish tank to the growing bed and allow it to drain back into the fish tank. But “flood and drain” systems often use a simple Bell Siphon to control the water flow. The siphon allows the water level to rise in the growing bed until it reaches a point where the siphoning action is started, then the siphon drains the water to the bottom of the grow bed, where the siphoning action is broken and the bed begins to refill from a pumped supply. This cycle repeats periodically according to height of the siphon and the volume of the water flow and growing bed. Variations can add sump tanks to buffer the water volume changes across the system.

Fish excrete ammonia in their waste.
Bacteria in water convert ammonia into nitrites.
Other bacteria in water convert nitrites into nitrates.
Plants absorb nitrates to grow.
Plants supply fish with food.

Advantages of aquaponics:

  • Higher production yields from less space and less time
  • Reduction in water usage
  • No need for chemical fertilizers
  • Closed loop with no environmental impact
  • Good control over growing environment
  • Year round production is possible
  • Low maintenance once setup and started
  • Reduction in plant diseases

Disadvantages of aquaponics:

  • Higher initial cost and setup effort
  • More knowledge required at startup
  • Power required for water pump
  • Weight may be an issue, depending on configuration
  • A greenhouse and monitoring sensors can add overhead
  • Configuration tweaking can be tricky
  • Some points of failure are critical (pump)

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