What happens to toilet paper

Sewage treatment plantsThe dilemma with damp toilet paper

The large sewage treatment plant in Cologne, Stammheim. The largest sewage treatment plant in North Rhine-Westphalia. In dry weather, almost 5,000 liters of wastewater arrive here every second. Inside: Lots of rubbish. Cotton swabs, for example. Sanitary napkins. And damp toilet paper. Martin Grudzielanek, Head of Operations Management in Stammheim, explains the so-called computer system. This fishes the coarsest rubbish out of the wastewater.

"The computer is constructed in such a way that vertical rods stand in the water flow with a rod spacing of 8 mm and everything that is now in the wastewater over 8 mm remains hanging on these rods and with this rotating rake that you can see here in front, This screenings are taken out of the wastewater. The whole thing is put on a conveyor, is pressed and then loaded into containers, which then goes to the waste incineration plant. "

Main component: tear-resistant fleece

But a lot also slips through the slide rule. This is not a problem with normal toilet paper: it consists of cellulose and dissolves so strongly in further wastewater treatment that it does not play a major role for the pumps that convey the water in the sewage treatment plant. Moist toilet paper, on the other hand, is not made of paper, but of tear-resistant fleece, i.e. textile fibers:

"These wet wipes are made in such a way that they do not dissolve and when they dissolve, they form long braids due to their structure and on these braids, in turn, hair gets stuck, which is of course in the sewage and other things, like that that the whole thing is quite compact and these compact braids, for example, ensure here in Stammheim that many pumps are already destroyed for us. "

Damp toilet paper in the trash

Martin Grudzielanek believes that damp toilet towels belong in the garbage and not in the wastewater. Therefore, consumers should be better educated. But in fact there are no clear rules as to whether the damp toilet paper belongs in the toilet or not. Instead, it is just a kind of voluntary commitment by the manufacturer. A few years ago, the European Association of Nonwoven Manufacturers decided at which dissolution rate a wet wipe could be described as "flushable".

The prerequisite for flushability is that the wipes lose 25 percent of their mass within three hours in the water in the so-called "slosh box" test. In this test, the wet wipes are placed in a kind of small aquarium that is swiveled back and forth. The problem: The effect can hardly be compared with a normal flowing runoff in the sewer, says Professor Holger Schüttrumpf from the Institute for Hydraulic Engineering and Water Management at RWTH Aachen University. The continuous flow of the wastewater in the institute's so-called circular channel is simulated more realistically: a round pipe construction in which the cloths in the water swirl endlessly in a circle. Holger Schüttrumpf tests moist toilet paper from various brands here.

Ordinary toilet paper will dissolve

"If you now look at the differences, no matter which one you use - that is now damp toilet paper: You can see that it has retained its structure, its shape even after two hours in the water. If we compare it with conventional paper toilet paper "Then you realize that it disintegrates over time, it dissolves and I also notice that individual fibers stick to my hands."

The test shows: The friction in the sewer system alone is not enough for the damp toilet paper to dissolve quickly. The cloths are washed ashore with a lot of other garbage like a carpet in the sewage treatment plant.

Declaration of war on the damp toilet paper

The large sewage treatment plant in Stammheim has now declared war on them with so-called macerators, explains employee Martin Grudzielanek:

"Like large pumps, macerators are only equipped with a large cutting unit, so that these substances, which do not dissolve by themselves or which form these pigtails, are practically shredded by this cutting unit, so that no further noteworthy blockages occur within the pipelines in the further course of the process . That is the solution."

Quite an expensive solution. Ultimately, the costs are borne by consumers - through higher wastewater charges. Simply throwing the damp cloths in the bucket instead of in the toilet would be much cheaper - for everyone involved.