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A prototype Testfilter within a ship - Why?

For a good year we are working an a practical proof to our technical feasability study. We want to build a prototype testfilter system and today we write about it.

The Filter system

Our planned filter consists generally from sand and gravel in different sizes and water plants. Impurities within the water will be kept in the space between the gravel. And the plant's roots will "eat" up the leftover and thus clean the filter. Thats the theory. This technique is well known and used all over the world, but it hasn't been implemented into a streaming river. Berlin Spree water quality varies enormously and especially after heavy rain and sewage overflow it can turn seriously bad. The filter must react on very different incomming water grades but must maintain its filter capacity in order to release water with bathing quality. This is a huge challenge.

Schematic illustration on filtersystem with its different vertical layers

To confirm the results of our Technical feasability study we would want to built a prototype filter system. For concept and planning process in the end of 2015 we commissioned engineers at AKUT Umweltschutz Burkhardt und Partner and Pecher und Partner together with Kompetenzzentrum Wasser. A scientific overview is given by Prof Heiko Sieker from Ingenieurgesellschaft Prof. Dr. Sieker.

Planning steps

An illustration of the proposed testfilter within the chamber of the former lock. The fresh water basin is on the lower water level of the canal

A first draft placed the prototype filter within the chamber of an old and deactivated lock with around 100 sqm in size. But due to incalculable constraints we skipt this idea and since spring 2016 we focus on a system that can be loaded into a ship.

The ship

Aft of "Hans Wlhelm" in its previous position in Berlin Lichtenberg

The ship will be a barge named "Hans Wilhelm" with a length of +40 m long and a width of 5 m. It belongs to Berlin Brandenburgischen Schiffahrtsgesellschaft e.V., better known as "Historical Harbour Berlin". I a joint co-operation with them we improve the barge to gain seaworthyness since May 2016. Right now its been lifted into the Hegemann shipyard in Berlin Spandau, where it has been examined, stripped from rubbish and waste from several years, replaced front and aft of the hull and soon repainted in full. Then it can be lowered back into the water and the construction of the test filter can begin.

A prototype filter within a barge

The three cargo bays of "Hans Wilhelm", each about 55 m2 in size, serve as structural shell for the filter system. There will be three filter basins with about 24 m3 capacity each, half of the size will be filled by gravel and sand, which serve as a filter layer, through which the water flows and being purified. In addition, there will be a "mussel reactor" basin. During the planning phase we have learned that mussels have a tremendous filter effect, so we want to test that within the prototype.

A final basin is called "fresh water tank" and shall simulate the future swimming area on about 70m3 in volume. We calculated a necccessary daily filter volume of the size of the swimming area as a result of our technical feasibility study, which means all the water within it needs to be exchanged once per day and be replaced by filtered water. Thus we expect the water quality remain within swimming waterquality parameters.

To be sure, we want to monitor the water quality at the beginning and end of the fresh water tank and check as to whether the filtered water maintains the necessary quality, or does not fall within the predetermined benchmarks. In this case, the filter configuration must be adjusted in at least one filter basin. The three filter basins are working parallel to each other, so we are able to provide different configurations in a short period side by side. It takes a certain time until a single filter "retracted" itself. Eventually it is a complex biological process, which is also subject to changing water qualities of the Spree.

The technical difference of our prototype filter compared to the future filter system is that we need to pump the water into the basins and at the end out of it again, because we can not cut a hole in the barge's hull and let Spree water poruing in in a natural way. Then the barge would not be a ship but only a shipwreck.
Section through the prototype testfilter system (Kammer = Cargo bay), drawing: AKUT. the blue area shows the max. operational depth level


When the prototype filter will be running a series of sensoric and laboratoric parameters will be checked on a regular base. There will be water analyses at the beginning, when it's pumped out of the canal and into the first basin. Then there will be analyses at the end of each filter basin in order to check their individual filter performance. And at the end of the freshwater basin we will execute more analyses to test if water quality is still good enough after a day within the basin. All collected data shall be evaluated and visualized. Currently the Research group Creative Media within the University of Applied Science, Berlin is working on a feasability study to present some drafts on how that can be done.


Mock-up of possible water data visualization

Our aim is to gain enough practical results out of the prototype testfilter by the end of 2018 to be able to configure the future "real" filter system which needs to be build within the whole width of the canal.

Our barge "Hans Wilhelm" is a historical standardized ship with a twenty meter vertical pole, it will be refurbished, re-painted and loaded with the prototype testfilter as cargo. It hopefully will settle in front of the Ministry of Foreign Affairs just before the weir to reach the best and as close to realistic as possible water situation and of course to re-live a tradition on-site: Until the late 19th century this canal used to be the main shipping canal in Berlins city centre and thus crowded with this kind of barges.

Today in this strech of the canal ships are prohibited. For our barge it means writing a lot of papers and apply for a lot of permits. Not an easy way but we are optimistic to eventually see the barge right there, where we want it to be by late summer or beginning of autumn this year.

Friedrichsgracht Canal 1934 with Virgin Bridge (Jungfernbrücke) and Mühlengraben, (Photo: Political Archive, Misistry of Forreign Affairs)