Aquaponics

Fish production from aquaculture and plant production from hydroculture have something in common: a tense relationship to nitrogen.

In aquaculture, nitrogen compounds dissolved in the water are formed as a by-product. Since these can be harmful to the fish, one tries to get rid of them there. However, simply discharging these nitrogen-rich effluents into the environment would on the one hand be a burden on nature and on the other be a waste of resources. Sophisticated filter- and degassing-systems are therefore used trying to free the water from nitrogen.

Plants in hydroponics (soilless hydroculture) require dissolved nitrogen compounds in the water to grow. These are provided, especially in commercial hydroponic facilities, in the form of artificial fertilizers. However, the production and transport of fertilizers is associated with a high consumption of resources and a negative impact on the environment.

Aquaponics is an approach that combines aquaculture with hydroponics under one roof using a shared water cycle.

What is produced in one place as an annoying by-product is to meet urgent needs elsewhere. An optimally controlled connection between fish farming and plant cultivation promises several attractive synergies:

• Shared water - aquaculture water is recycled for the irrigation of plants and can thus be used more efficiently.
• Shared nutrients - Aquaculture's "waste-water" is full of valuable nutrients needed for plant cultivation.
• Shared energy - Many aquaculture species are happy to have it warm. The same applies to many plant species in hydroponics. A common heating system can reduce heat losses and thus contribute to an increased energy efficiency.

What sounds simple at first glance turns out to be extremely complex.

Each species, aquatic or terrestrial, has different environmental and food requirements. To find combinations of organisms that harmonize well with each other is therefore a great challenge.

Nutrient composition matters

Although the aquaculture water is full of nutrients, these are not necessarily in the chemical form preferred by the plants. To prepare these in such a way that they are optimally usable in form and concentration for the plants is one of the great challenges of aquaponics.

Bacteria serve as useful helpers

A large portion of the nitrogen discharged from fish is in the form of ammonium. But ammonium is highly toxic to fish. Some bacteria, on the other hand, can use ammonium as a source of energy and produce nitrate as a metabolic end product, one of the most important nutrients for plants.

Aquaponics offers great potential for the sustainable production of food.

In order to make this potential available in praxis, however, there are still some hurdles to be taken.

An intelligent control and coordination of nutrient dynamics within aquaponic systems is essential and requires further research.