Sewer network operators have a higher responsibility, which is wastewater management. Undisrupted operation is a top priority, and heat exchangers in the sewer are therefore only approved if they do not cause any restriction in the management of the sewer network. We meet this requirement with the Therm-Liner system. Our heat exchangers can be installed during ongoing sewer operation and actually benefit from regular sewer cleaning, which a heat exchanger system must not restrict or impede in any way. In 19 of the 25 largest cities in Germany, the sewer network operators now approve the installation of sewer
heat exchanges, led by Berlin. The sewer operators often receive a usage fee, which covers the small amount of administrative work that they have to do. This fee has also increased the willingness of the sewer network operators to look at wastewater heat, or the energy potential in their own networks. Some sewer network operators have already illustrated their potential in energy maps, which are now available online. It is thus now possible to check a particular location in seconds to see if energy from wastewater is an option.
One of the network operators’ frequent reservations earlier was the cooling of the wastewater by the removal of energy. It is correct that thermal energy is removed from the wastewater when wastewater energy is recycled. The wastewater is cooled. But it recovers very quickly too, through the inflow of new wastewater and because it absorbs ambient heat through the sewer. The rule of thumb is: A system for recovering energy from wastewater needs a recovery line afterwards around two to three times the length of the plant itself, and then the temperature of the wastewater has recovered again. If a system is 100 m long, the wastewater has regenerated itself in terms of energy after 200 to 300 m at the most. Consequently, for the sewage treatment systems, which generally assume a minimum temperature of the wastewater, the only deciding factor is how much heat the last system withdraws from the wastewater before the sewage treatment plant and how far this is from the sewage treatment plant. The removal of energy in the network beforehand is irrelevant for the
sewage treatment plants. The wastewater cooling is thus not a restriction on the extraction of energy from wastewater.
