How is wastewater processed into clean water

Sanitation Down the drain and then?

Almost 1.9 trillion liters of wastewater flows through Bavaria every year, more than half of it from private households and businesses. Flushing the toilet, washing machine, dishwasher, all of these things add up to a lot of dirt. From the rinse - out of sight, out of mind.

After the sewage treatment plant comes the river

At the very end, all the water ends up in Bavaria's lakes and rivers. The sewage disposal system ensures that you do not encounter what you washed down there again. Around 104,000 kilometers of public mixed and wastewater canals in Bavaria direct the wastewater into the municipal sewage treatment plants, where it is cleaned. A hungry army of tiny helpers works there:

Almost 1.9 trillion liters of wastewater per year in Bavaria A little more than half of the wastewater comes from private households and businesses. Additional wastewater from industry flows into public or in-house sewage treatment plants. And rain is another great source: Contaminated by air pollution, road dust, tire wear and the like, the rainwater has to be cleaned - around a third of the total amount of wastewater.

The sewage sludge challenge

Dried sewage sludge is sometimes applied to fields as fertilizer or burned.

The treatment of wastewater in Germany produces around 2 million tons of sewage sludge (dry matter) (as of 2017). In sewage sludge there are nutrients (such as phosphorus and nitrate) but also pollutants such as heavy metals and drug residues, which are separated from the sewage sludge during wastewater treatment.

Copied from nature: plant sewage treatment plants

A herbal sewage treatment plant

In principle, sewage treatment plants work no differently than nature itself: Even overgrown soil filters the water that seeps through it and cleans it of toxins with the help of microorganisms. This is what makes our groundwater so clean. Small, "near-natural" sewage treatment plants work according to the same principle: In plant sewage treatment plants, marsh plants filter the wastewater and, with their roots, offer a habitat for the bacterial colonies that pounce on the microbiological wastewater treatment.

With the amount of polluted water that we produce, however, nature would be completely overwhelmed. And also with what now ends up in our wastewater. Even sewage treatment plants are reaching their limits.

New methods against pathogens in wastewater

Wastewater is an ideal habitat for bacteria and viruses. The biological stage of the sewage treatment works cannot harm them, because microorganisms should feel comfortable in the aeration tank in particular. For a long time this led to a veritable contamination of rivers and lakes into which the clarified water was discharged.

Ultraviolet light against germs

Nowadays, individual sewage treatment plants disinfect the wastewater with UV light (ultraviolet light), which kills germs in seconds in an efficient and environmentally friendly manner. Bad Tölz was the first sewage treatment plant in Bavaria to switch on the UV lamps in 2000. Since then, numerous sewage treatment plants on the Isar and Loisach have been irradiating the wastewater, at least in the summer months. The Isar thanks you: After years of bathing bans, your water is now bathing quality again.

Another method of effective disinfection is used at the sewage treatment plant in Monheim: There a membrane sewage treatment plant filters the water through the straw, so to speak. Bacteria and ninety percent of viruses simply do not fit through the hollow fiber membranes that the water has to pass through. What arrives at the other end of the stalks is almost of drinking water quality.

Still unsettled in the water: Medicines & Co.

With materials that are even smaller, however, hollow fiber membranes are of no use either. And it is precisely such micropollutants and nanomaterials that are increasingly found in wastewater: Many pharmaceuticals, cosmetics, cleaning agents and other household and industrial chemicals can hardly be filtered out at all because conventional three-stage sewage treatment plants are not designed for this.

Micropollutants can currently not be filtered out sufficiently by conventional sewage treatment plants.

A fourth purification stage could help here, using, for example, activated carbon filters, oxidation processes or other membrane processes (nanofiltration and reverse osmosis). According to the Bavarian Ministry of the Environment (StMUV), there is currently neither a legal obligation nor an acute need to act for the so-called "trace element elimination" for the introduction of the fourth stage. However, 90 of the around 2,500 existing sewage treatment plants in Bavaria have now been selected on the basis of "technical criteria", according to the StMUV, which are suitable for the expansion of a fourth treatment stage. Voluntary expansion measures for these plants are to be subsidized by the state.

Large data gaps in Bavaria's sewer system

There is another weak point in Bavaria's wastewater disposal: the sewer system. Because the approximately 104,000 kilometers of public canals that are supposed to clear all the polluted water have been completely out of sight for a while. So much so that an initial inspection was ordered for the entire sewer system in order to determine its condition at all. At the end of 2010, this had not yet been done for a third of the channels. In July 2018, 14.5 percent of the sewers are in need of renovation. Risky, because every leaky sewer endangers our groundwater.

The private sewerage part

The real sticking point in the sewer system is not even included: the private part. In addition to the public sewer system in Bavaria, there are also sewers for which homeowners are responsible. The sum of these private and non-public channels is estimated to be about two to three times the length of the public sewer system. And so far there is no central condition assessment for these.

The Bavarian State Office for Environmental Protection assumes that up to 80 percent of private sewer pipes are leaking, because they were often neither built by a specialist company nor according to the rules of technology. And then usually only rarely checked. Often homeowners do not even know that they are also responsible for the sewer system. Because not only the sewage pipes in the house, but also all pipes that run under the house and in the ground, must be checked and kept tight by the house owner himself.