Cleaning up the Elbe ...
RWTH Alumni Visit the Metha Silt Treatment Plant
Despite the very windy and rainy weather (the tail end of storm Joshua was still clearly in the air), 11 alumni from RWTH Aachen University set off for Hamburg Finkenwerder on the afternoon of October 28, 2025. Their destination was the Metha silt treatment plant. Metha stands for “mechanical separation of harbor sediments” (in German), and it is operated by the Hamburg Port Authority (HPA).
Operations manager Karsten Lehmann, a biotechnology engineer, greeted us and gave us a very informative presentation that explained the tasks and operations of the plant. In order to keep the Elbe shipping channel clear for navigation, it must be dredged regularly. This produces approximately 3 million tons of silt per year. Most of it is “relocated” elsewhere in the river or dumped in the North Sea.
However, not all sediments can be relocated as they are contaminated with heavy metals, such as arsenic, and other substances. Metha deals with this part of the silt. Since the plant went into operation in 1993, around 277 tons of arsenic, 788 tons of lead, and 552 tons of chromium have been filtered out.
Artificial whirlwinds
This theoretical introduction was followed by a trip out into the rain. After a quick look at a basin measuring around 300,000 cubic meters, where the dredged sediments are temporarily stored, we went into a huge hall where the processing takes place. It was warm and dry here, but very noisy, and our noses told us that we were dealing with rather unpleasant substances.
At the heart of the plant are several hydrocyclones which generate artificial whirlwinds. This centrifugal process causes the toxic fine sand sediments to rise and the coarse sand to slide down. Presses that exert a pressure of five bar squeeze out the water.
The clean sand can then be used as a building material, for example in dyke construction.
The contaminated material is mixed with flocculants so that it thickens and it is then dehydrated in presses. Any material that cannot be reused, for example in brick production, is then used in landfill construction.
After a final round of questions, we said goodbye to Mr. Lehmann, but not without thanking him for giving us the opportunity to visit this impressive facility and for his detailed and expert explanations.
Afterwards, nine alumni met at the restaurant “Finkenwerder Landungsbrücke” to enjoy good food and drinks, talk shop, and speculate about future meetings. After thanking the organizers in Aachen, everyone then set off for home.
– Authors: Christoph Schröder and Winfried Sturm