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The plant seems to have assembled Daniel Gullwing or Doc Brown. On a red frame are several different containers connected by a tangle of tubes. Large boxes filled with acid on the floor. A lab worker wearing a respirator and gloves shovels a red-brown substance that looks like wet sand from one of the containers in a plastic bag.
Two other frames are completely covered with Plexiglas glass, the ventilation system reveals: what is there stinks. In the frame boxes are to be recognized in a turbid stirring, which is constantly mixed by a stirrer. Again, pipes, pumps, cartridges. And then there is this glass container in which flows a clear liquid of the consistency of an expensive grappa. But you should not drink the liquid. It is phosphoric acid. The end product of this complex device. At the beginning, there is the brown-red substance: ash of sewage sludge
Only three companies have the necessary know-how
We are located in a discreet industrial building in the outskirts of Madrid. Here is the research laboratory of Técnicas Reunidas. Tecnicas Reunidas is specialized in the development of new chemical processes, mainly in the field of electrochemistry and hydrometallurgy. She works among other things for the companies of products and oil. And for the Canton of Zurich, specifically for the Hinwil Foundation ZAR (Center for the Sustainable Use of Waste and Resources)
The ZAR Foundation was entrusted by the Cantonal Office of Waste, Water, Energy and Air (Awel): Develop and implement a method of recovering phosphorus from ash sludge. Founded in 2010 by the canton of Zurich and the waste recyclers, the foundation itself develops various recycling processes. For the recycling of sewage sludge, however, the ZAR was looking for and found a suitable partner in Técnicas Reunidas. It is one of only three companies in Europe to possess this know-how.
"What works on a small scale also works on a large scale.Only the containers become bigger." Stefan Schlumberger, Chemist
Phosphorus is a central chemical component of all life and the component The main source of all mineral fertilizers is usually phosphorus used by fertilizer producers from abroad, it is mined in huge mines and Switzerland imports about 4500 tons a year. [19659002] Ecologically, it does not make much sense Phosphorus degradation is harmful to the environment.Also, many phosphorus ores contain uranium and cadmium; Radioactive substances are found in fertilizers, accumulate in soils and enter drinking water.Although there are pollutant limits for fertilizers, but these are often not respected. .
At the same time, Switzerland would not need to rely on imported phosphorus, it has more than enough: in wastewater. We humans excrete the substance among other things in the urine. Sewage treatment plants are obliged to precipitate phosphorus. In the past, farmers used sludge directly as fertilizer, but this has not been allowed since 2006, as it releases not only heavy metals but also pathogens and residues of medicines and cosmetics in the fields. . Since then, sewage sludge has been burned. In the canton of Zurich, this is done in a separate incinerator in the Werdhölzli – leaving about 12,000 tons of ash per year, and this ash contains about 1,100 tons of phosphorus.
The recycling of sewage sludge is mandatory
But now, it is necessary that the phosphorus – on a national scale – fall from about 6000 tons per year – must be recovered from 2026. This is what the Federal Waste Act requires. This is the reason why the canton of Zurich in Madrid has tested the recycling process, which he calls "Phos 4 Life".
The procedure that many pipes and containers allow visitors to guess is complicated. "We worked there for three years," says Ángel Galindo Carbajo, Business Development Manager at Técnicas Reunidas. The problem: the ashes of sewage sludge contain a lot of sand and a lot of unwanted substances like aluminum, arsenic, copper and especially a fifth of iron. Because iron chloride is the substance that sewage treatment plants add to wastewater to bind and precipitate phosphorus.
All these substances should be eliminated as much as possible. This happens on several stages with the addition of sulfuric acid and hydrochloric acid. For six weeks, the researchers tested the process at the pilot plant and worked in detail, with 25 people working 24 hours a day in three shifts. In total, the development of "Phos 4 Life" has devoured about six million francs, half of which is supported by the canton of Zurich.
Not Distinct From Conventional Phosphorus
But the effort was worth it. Stefan Schlumberger is convinced of that. The chemist is at the head of the hydrometallurgy competence center of the ZAR foundation.
It has been clear for several days that the procedure is working as intended. It provides phosphorus, which is chemically indistinguishable from the substance obtained conventionally and contains no pollutants. "This allows us to produce a product that all fertilizer manufacturers can use," explains Schlumberger. This distinguishes "Phos 4 Life" from other, simpler methods for phosphorus recovery.
Moreover, and this is another big advantage for Schlumberger, there is no unacceptable or even dangerous residue left. The sludge can be recycled almost 100%, in addition to phosphoric acid, the process provides, for example, sand and gypsum for the production of cement and various metals. Unlike conventional phosphate extraction, the method is also environmentally friendly. This is shown by an LCA study by ETH.
The objective: to treat 2.5 tons of ash per hour
The only catch: even if the resulting phosphorus can be sold at market prices, the process increases the cost of the elimination of sewage sludge. These costs must be borne by the polluter, ie the households, via the sanitation fee. However, this is not very noticeable, says Schlumberger: "The extra costs are about five francs a year per household."
Now is the time to plan a large-scale system. Where she comes to stand is still unknown. One thing is certain: the knowledge acquired in the pilot plant can be transferred head-to-head. "It's the benefit of chemical processes," Stefan Schlumberger explains, "what works on a small scale also works on a large scale. The processes remain the same, they also take the same time. Only the containers are bigger. In Madrid, the pilot plant treated 500 grams of ash sludge per hour, at the final stage it should be 2.5 tons
. (Tages-Anzeiger)
created: 15.07.2018, 15:38
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