Tilapia and tomato being farmed together by combining aquiculture and hydroponics. . (Photo Credit: David Besa/FIS)
Tilapia and tomatoes farmed together in a sustainable setting
Friday, July 05, 2013, 04:10 (GMT + 9)
The Institute of Freshwater Ecology and Inland Fisheries in Berlin is growing tomatoes and fish together, since it has been found that dirty water from the fish tanks can provide nutrients to the tomato plants. The goal is to grow vegetables and farm fish in zero emission conditions.
A few hundred tilapia are being raised in a dozen fish tanks in a greenhouse together with numerous tomato plants. The temperature is kept at 27 degrees Celsius.
The fish are kept humanely, says Werner Kloas, founder of the greenhouse: each tank contains just one school of fish, which is a similar density to that found in their natural habitat. And the tomatoes are planted in mineral wool instead of soil.
The researchers have demonstrated several times that the venture is successful, Deutsche Welle reports.
Fish excrete ammonia, which is toxic for tilapia, so the water must be treated -- and this dirty water is an ideal fertilizer for tomatoes once the fish waste has been filtered and the ammonia has been chemically removed.
It happens automatically: the dirty water runs through white plastic pipes and fish waste is filtered out, after which the water is purified in a biofilter.
A byproduct is nitrate -- an essential and valuable component of plant fertilizer. The treated water is then transferred via pipes to the boxes where the tomato plants are growing.
The plants then absorb nitrate from the water and any extra is eliminated through the leaves as water vapor. Several cooling traps installed under the ceiling ensure that the water vapor returns to the fish tanks.
"With such a closed loop system, we only need to use about 10-per cent of fresh water a day," says Kloas. "We can save so much water and therefore manage a sustainable system."
The researchers believe that this system would be a profitable and practical way for drought-stricken areas in Africa, for example, to produce food.
Yet although evaporated water is extracted from the greenhouse via cooling traps and re-fed into the water system, the energy required for such a system is huge. Werner Kloas believes that simple solar systems would be enough to generate energy year-round if such systems were installed in Asia, Africa and South America.
By Natalia Real