Why do rains pollute the water

Wastewater storage for clean Spree

Ralf Steeg, who had the idea, opens the large lid of the tank. Under the approximately 300 square meters of lattice walkway there are three 50 meter long tubes with a diameter of two meters.

"The system has been standing for a year now. The first rain event was on April 22. We have now had ten fillings. So far, we have collected over 5000 cubic meters of wastewater in the system. If the wastewater were to be filled into tankers, that would be 138 pieces one after the other. I think that's a lot. "

Although this first system is only a small one. When a sewer system is built today, the streams are separated. Wastewater from the houses is fed to the sewage treatment plant and the rainwater from the streets directly into the river. But the Berlin city center has a so-called mixed sewer system. Prof. Matthias Barjenbruch from the TU Berlin, who is scientifically accompanying the project, explains:

"The whole thing developed. At first there was no sewer system. And then the water toilet was introduced - compulsory - first in London, later in Berlin and in other cities in Europe. That was still a luxury back then. So you had the simplest solution was to put a pipe under the street to collect the sewage and dirty water. In the beginning you didn't have any sewage treatment plants, you dumped everything into the rivers until you noticed that the rivers were strong pollute, no oxygen, fish die. "

Then sewage fields were first created, later sewage treatment plants were built. But when there is a heavy thunderstorm, they cannot absorb all of the water. Then rain and sewage get into the Spree through emergency overflows. Unfiltered and uncleared. 15 to 20 times a year.

"In Berlin we have around 220 million cubic meters of super-quality wastewater that is cleaned by the sewage treatment plants. And then we have maybe ten million that go over these overflows, which are not cleaned, and get into the water with pollution. And Then we still have the area where we previously thought we are relatively clean: This separation system, where the rainwater is discharged from a second canal. The streets are dirty, car tire abrasion, combustion residues, dog excrement, in winter still that Grit. Everything goes in untreated in the separation system. So something still has to happen in the separation system. "

One of these emergency overflows in the Berlin mixed sewer system now ends in Luri's tank. Watersystems. Managing Director Ralf Steeg:

"This is where the wastewater is stored. And when the sewer system is free again after the rains, it is pumped back into the sewer system, reaches the sewage treatment plant and is cleaned there. But we can also equip it with systems for wastewater treatment. Then we pump it Wastewater is no longer returned, but cleaned on the system and can then be discharged directly into the rivers and seas, in a clean state. "

Even if his tank should overflow, he has still caught the first surge of dirt, later water does not bring as much dirt, and this sinks in the tank as it flows through. The need could be great, because Berlin is not alone with the overflow problem.

"We have this problem all over the world, in New York, London, Paris, Tokyo. That means that all big cities around the world have had the same problem since about 1870."

The landscape architect and environmental planner Steeg sees another aspect of the tanks. They could be included in urban planning and the surfaces could be used as islands, as a café on the water, boat rentals, or a sunbathing area. In Berlin that was initially undesirable - from the district administration. So it's just a technical looking lattice walkway.

"I imagine that there are some islands that you can't even go to, on which, for example, just birds nest. And other islands are there so that you can hold public events. The surfaces can also be marketed and the rents can be used to partially refinance these systems. "