Sewage plants in the future provide valuable phosphates for unencumbered Fertilizer
In addition to potash and nitrogen include phosphates to the main fertilizers. In a few decades they will be depleted, at least those who are not contaminated by toxic heavy metals. The European Union has added phosphates a year ago in the list of strategic raw materials whose supply is no longer ensured in the long run. Germany and other industrial nations bow before. They have developed techniques with which phosphates can from the mud that accumulates in sewage treatment plants, to recover.
In sludge contained phosphates are hardly used.
Germany consumes nearly 300,000 tons of phosphate fertilizer per year. Some of it ends up because of over-fertilization in rivers and streams and lakes, with sometimes fatal consequences. The algae growth is stimulated excessively. There is a risk that lakes upset by lack of oxygen, caused by decaying plants on the ground, to stinking pools. Humans and animals excrete phosphates. They although are vital, but what is too much is too much. It ends up in the sewage treatment plant, in large quantities. But the people in Germany divorce each year from around 58,000 tonnes. Until now, the precious substance remains in the sewage sludge, which is ultimately mostly burned. The ash is landfilled. Only a small part of the sludge still ends up as fertilizer in the fields, because always the risk that toxic heavy metals contained. Therefore, the waste water treatment plants to go now because regain the mineral. A pilot plant is being built in Linz-Unkel am Rhein. The sewage sludge is initially placed in the digester. Here Miktotganismen use the nutrients to produce methane. This is burned in engines that drive generators to produce electricity.
Investment in recovery plants are aimed at increasing
The phosphates survive the procedure in the digester without prejudice. In a recovery plant, which will cost 2.4 million euros, the phosphates are separated so that they can be used for fertilizer production. Currently, several recycling technologies compete with each other. The most sophisticated present researchers at the Fraunhofer Institute for Silicate Research (ISC) in Würzburg. You have particles that are magnetic, surrounded by a shell of silicate. These tiny particles are simply tipped into the dirty broth spills in the clarifier. Silicate Phosphate attracts irresistibly. After a while, all the particles are saturated. Magnets fish them out. By ion exchange, the Würzburg researchers recover the phosphates.
Other water researchers rely on chemical precipitation so-called. These chemicals are used which bind phosphates per se. They are removed from the waste water and separated, so that the valuable substances can be reused.
In another method, the sludge is first burned. From the ashes are mineral phosphates which defy the combustion temperatures, removed. In several sewage treatment plants in Germany, there are already pilot and test facilities where recycling techniques are being tested. Would they introduced throughout the country, Germany could meet a third of its phosphate needs through recycling, according to experts. So far, the still fails because of the cost.