Waste water from sewage treatment as fertilizer

Waste water from sewage treatment as fertilizer

5:03 AM, 8th August 2012
Waste water from sewage treatment as fertilizer
Composed of reclaimed wastewater, high-quality fertilizers release nutrients.

MUNICH, GERMANY: Sewage sludge, sewage and manure are valuable sources of fertilizer can be won for the production of food. Researchers now have a chemical-free and environmental friendly process to develop, with the recovered salts directly converted into fertilizer. Phosphorus is important not only for plants but for all living things. But this is an essential element for the production of food is scarce. One indication is the constantly rising prices for phosphate fertilizers. 

High time then to look for alternatives. Not an easy task - because phosphorus cannot be replaced by another substance. A solution, researchers have found by the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB in Stuttgart. Use existing resources in this country - and found just in waste water from sewage treatment plants or digestate from biogas plants. The alleged dirty broth can be recycled outstanding. Therefore, scientists around Jennifer Bilbao, directs the IGB Group for nutrient management, have developed a new method. “Here, nutrients are made so that it directly as a fertilizer available,” said Jennifer Bilbao.

Core of the patented method, the test, the experts are currently in a mobile pilot plant is an electrochemical process that uses electrolysis to nitrogen and phosphorus as magnesium ammonium phosphate - are precipitated - also known as struvite. The struvite salt is excreted from the process water in the form of small crystals, so it can be used directly as a plant fertilizer. The highlight of the method: In contrast to conventional methods, the researchers have to admit no salts or alkalis. “It is completely chemical-free is a process,” added Bilbao.

In the man-sized electrolytic cell of the test facility through which the wastewater is passed, there is a sacrificial anode made of magnesium and a metallic cathode. During the electrolysis, the negatively charged pole, the cathode, the water split. It will be formed including hydroxide ions. At the positively charged pole, the anode takes place, oxidation: magnesium ions migrate through the water and react with the contained in the solution of ammonium phosphate and struvite.

Since magnesium ions are highly reactive substance in the process water in the system is required for this process is very little energy. Therefore less power for the electrochemical decomposition is needed than with conventional methods. In all previously studied wastewater was below the required power 70 watt hours per cubic metre - a very low value. Long-term experiments also showed that the phosphorus concentration in the reactor decreases the pilot plant by 99.7 per cent to less than 2 milligrams per liter. This fell below the limit of the researchers from IGB Wastewater Ordinance (Wastewater Ordinance) for sewage treatment to 100 000 inhabitants.

“Wastewater treatment plant operators would thus be able to connect with the lucrative production of fertilizers, sewage treatment,” said Bilbao. The product of struvite is attractive for agriculture because it is considered a high quality fertilizer that releases nutrients slowly. Growth experiments of Fraunhofer researchers confirmed the effectiveness of yield and nutrient uptake by plants were struvite with up to four times higher than commercial fertilizers.

© Fraunhofer-Gesellschaft News

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