From August 2027, an EU directive will require significantly more nitrogen and phosphorus to be removed from municipal wastewater. Researchers at the Institute of Chemical Engineering at Ulm University have therefore, in collaboration with the Steinhäule Sewage Treatment Plant Association, developed a process for removing ammonium and set up a pilot plant. The nitrogen contained in the process water is to be recycled in future. The process has recently begun testing on-site at the Neu-Ulm sewage treatment works.

If too much nitrogen and phosphorus enter waters that were originally nutrient-poor, the consequences are far-reaching: ammonium is toxic to fish, and the nutrients stimulate growth of algae and aquatic plants. The water becomes cloudy and loses oxygen, leading to a loss of biodiversity. To prevent, amongst other things, this so-called eutrophication of water bodies, the European Union has adopted a new Urban Waste Water Treatment Directive: it obliges local authorities to remove significantly more nitrogen and phosphorus from their sewage treatment plants than before, with effect from August 2027. Some of this nitrogen is present in the wastewater as ammonium. This is where a project by the Institute of Chemical Engineering at Ulm University comes in: Under the leadership of Professor Thomas Grützner, researchers and the Steinhäule Sewage Treatment Plant Association (ZVK) have developed a process for removing ammonium from wastewater and, together with specialists in thermal separation technology from the company Iludest GmbH, have designed a corresponding pilot plant.

This plant has been undergoing testing at the Steinhäule Wastewater Treatment Plant in Neu-Ulm since May 2026. It is operated by the association of the same name. “The ZVK is very interested in the use of future-proof technologies in all areas of sewage treatment works, particularly those aimed at sustainability, resource efficiency and circular economy,” says Jonathan Fuchs, Department Head of Operations and Laboratory at the Steinhäule Sewage Treatment Plant Association, regarding the collaboration with Ulm University. However, the ZVK does not merely aim to remove nitrogen down to the new limit and beyond in order to protect water bodies, but also to recover and recycle it in future. The project group led by Professor Grützner, which also included Chiara Lukas, Lorraine Arzner and Yannick Waibel, has developed a process in previous projects in collaboration with the ZVK whereby concentrated ammonia water is recovered and only a small proportion of ammonium remains in the wastewater, which is then removed during the biological treatment process. “Ammonia water can, for example, be used to remove CO₂ from industrial exhaust gases,” explains Grützner.

“Significant added value for our region”
The plant design is based on steam stripping, a specific variant of thermal separation technology in which water vapour absorbs a highly volatile component from a liquid. To achieve this, in a column – put very simply, a vertical pipe – so-called centrate water, which is produced during sewage sludge dewatering and is heavily contaminated with ammonium, is fed in counter-current to the rising steam. The centrate from the digested sludge is heated to boiling point by the rising steam. In the process, the originally bound ammonium is released into the gas phase in the form of ammonia and is carried upwards out of the plant by the steam. The purified concentrate, which now contains only small amounts of ammonium, is discharged at the bottom of the column. The steam exiting at the top, including the ammonia it contains, is condensed. Part of the condensate is recirculated back into the column to concentrate the ammonium content in the condensate. The remaining part of the condensate can, if necessary, be further concentrated in an additional step – thus ultimately producing concentrated ammonia water.

“We are very proud to be supporting our local partner in the development and construction of this pilot plant, thereby generating significant added value for our region,” says Professor Thomas Grützner. The process developed by the researchers is now being tested on site at the Steinhäule sewage treatment works over a period of several months, with a view to scaling it up to industrial scale at a later stage.

Further information:
Prof. Dr.-Ing. Thomas Grützner, Institute of Chemical Engineering,
email: thomas.gruetzner(at)uni-ulm.de  

Text and media contact: Christine Liebhardt