At first glance, there's nothing at the Lankow Sports Park that appears to belong to the geothermal plant. Right in the middle of the FC Mecklenburg football club's parking lot stands only a small gray building. It may seem inconspicuous, but the filter house is an essential component of the Schwerin utility company's Lankow I geothermal plant. It's not coincidental that it's situated in the middle of a parking lot. This is where the second borehole of the geothermal plant is located: the injection well. The current parking lot used to be the old drilling site. This is where the cooled brine returns to its original rock stratum, the Postera, nearly 1,300 meters deep.

On its way down, the brine passes through a filter – hence the gray building is called the filter house. You might wonder why this is necessary since the brine was already filtered in the thermal technology room. The coarse filter there has a mesh size of 25 micrometers. However, the filters at the injection well have much finer meshes, capturing anything larger than two micrometers. This could include dissolved substances from the brine that have accumulated in the pipelines on their way. Over the years, these substances could clog the pores of the sandstone, making it difficult to return the brine. The additional filtration is therefore aimed at providing the best possible protection for the aquifer, the water-bearing rock layer underground. Technically, there are two filters in the building, but one is sufficient for ongoing operation. The second serves as redundancy, ensuring the system's reliability.

To prevent the cooled brine, around 20 degrees Celsius, and the brine heated to 56 degrees Celsius in the depths from mixing near the extraction well, it is guided back to its original rock stratum over a kilometer away. Due to the excellent properties of the Schwerin sandstone with its large pores, no pump is needed for this process; gravity alone is sufficient. Once at the bottom, the deep water gradually warms up again.

The high salt content of the brine makes it aggressive towards metals. Therefore, it runs in special plastic pipes and does not come into direct contact with corrosion-prone metal. The brine connection line from the geothermal heating plant to the Lankow Sports Park is also made of the plastic polyurethane. The 1,037-meter-long pipeline runs underground along Edgar-Bennert-Straße. Sensors are installed in the protective tube of the brine pipeline to warn of moisture ingress from inside or outside.