The Mainz sewer network

Wastewater is a general term for water that can come from various sources and is discharged through a structural system (i.e., a sewer).

These include:

• Wastewater = water contaminated through use
• Rainwater = precipitation water flowing off paved surfaces (houses, streets, etc.)
• Combined water = wastewater + rainwater

We use state-of-the-art technology to move and control enormous volumes of water underground. For this purpose, we have created a city beneath the city.
An 800-kilometer sewer network ensures that water from every location in Mainz reaches the sewage treatment plant. To achieve this, we utilize the natural gradient and, in areas where Mainz is as flat as a pancake, we lift the wastewater with the help of a total of 85 pumping stations.

Two systems, one goal: For historical reasons, there are two different sewer systems in Mainz's underground. In the past, the combined system was favored, in which sewage and rainwater were discharged into a single sewer.

For around fifteen years, however, separate systems have been the norm, with sewage and rainwater being drained separately. This has the advantage that rainwater does not need to be treated separately, but can be fed directly into a body of water or allowed to seep away on site.

Yes, we flush our sewers, which means we clean them. That may sound strange, but it's easy to explain. Due to Mainz's flat location, the sewers have little gradient. When little water flows through the sewer, sludge, sand, and fecal matter settle at the bottom. Added to this are things that don't belong there but unfortunately end up there time and time again: food scraps, wet wipes, cotton swabs, cigarette butts, etc.

To remove these deposits, we flush our sewers regularly. We have five state-of-the-art flushing trucks for this purpose. These combination vehicles are true recycling professionals. They flush the sewer at high pressure, then suck up the dirty flushing water, clean it in the vehicle, and are ready for the next job.

We don't just flush our pipes, we also film (opens in a new tab) them. This allows us to detect any cracks or other damage as early as possible.

Topographically speaking, Mainz is flat in many places. Remember the comparison with the breakfast board? This means that wastewater cannot flow to the treatment plant solely by means of a natural gradient. To overcome differences in elevation, we have therefore installed pumping stations and pressure pipes at the lowest points of the sewer system. These ensure that the water flows underground by balancing out the differences in elevation.

One of the largest and most important pumping stations is the Rheinallee pumping station. Wastewater from Mainz's Old and New Towns, Bretzenheim, Weisenau, Hechtsheim, Ebersheim, and the municipality of Bodenheim flows along the Rhine axis towards the wastewater treatment plant in Mombach.

Water needs space. Imagine a violent thunderstorm with continuous rain. Within a short time, a large amount of water flows through Mainz's sewers towards the sewage treatment plant. To prevent it from becoming flooded, most of the water is diverted into rainwater retention basins along the way. There are 77 of these in Mainz. When dry, they look like a depression in the landscape; when it rains heavily, they look like a small lake.

Rainwater retention basins fulfill several functions: they protect the sewage treatment plant from "overflowing," serve as temporary storage during heavy rainfall, and allow large quantities of water to return to the earth's natural water cycle through evaporation and seepage.

By the way: Large screens, weirs, and settling basins within the sewer system ensure that toilet paper residues and fecal matter are caught beforehand. This keeps rainwater retention basins clean.

However, more and more people are mistakenly using their toilets or drains as trash cans. Food scraps, wet wipes, paint, cotton swabs, and cigarette butts cause screens to clog. When a thunderstorm hits, fecal matter and toilet paper can then overcome the barriers and be carried by the floodwaters to places where they shouldn't be, such as a floodwater retention basin like the one at Lungenberg.

A settling tank is a tank with virtually no flow. It is used for the coarse cleaning of wastewater. Solid matter (sludge, sand, dirt) settles due to gravity, while the water continues to flow.
Settling tanks are found in both sewer systems and wastewater treatment plants. The principle is always the same:

low flow -> solid materials settle and can be removed more easily.

Our sewer system, which is around 100 years old, is a special gem that we care for and maintain every day.

Here (opens in a new tab) you can take a look under Boppstraße. You can see a brick sewer that was built at the end of the 19th century. Sewers of this type are still in operation today, virtually unchanged.

Mainz is growing steadily, and so is its sewer network. We plan, build, supervise, and implement projects of all sizes, from house connections to new city districts. Need an example? Just think of Layenhof, Zollhafen, or the former IBM site.