The Mellingen wastewater treatment plant was last expanded and overhauled between 1995 and 1998. At that time, the wastewater treatment plant was set up for a population equivalent (PE) of 23,000. However, the current workload for the wastewater treatment plant has already reached 30,000 PE, which is why planning for the expansion needs to be undertaken as soon as possible. TBF was commissioned to carry out the preparatory project, which included a comparison survey for the biological treatment stage. Given the limited space available at the wastewater treatment plant, the client opted for the development of a space-saving membrane bioreactor that cleans wastewater to bathing water quality. In addition to biological treatment, the project also included planning for the expansion of mechanical treatment and sludge treatment. As part of this, TBF covered the planning of all trades (ICE systems, HVAS, electromechanical engineering, construction technology, structural engineering, etc.). Following the preliminary project, TBF prepared and carried out the general planner tender with the client.