CFAS® from Biowater Technology – A smart way to upgrade existing plants for total nitrogen removal.

Due to the new stringent regulations by the European Wastewater Treatment Directive, the municipality of Damüls needed a way to achieve total nitrogen removal within their existing treatment plant.

DAMÜLS claimed in 2006 as the snowiest village in the world, Damüls is a small municipality in Austria. The municipality has its principal activities in the winter tourism. The population varies largely from the winter and the other seasons, which impacts the wastewater flow to be treated.


Biowater Technology was contacted by Dr. Richard Moosbrugger from IB-MR in Austria, the consultant of the Damüls Municipality in August 2020, and together worked to find the best solution to upgrade an existing plant to achieve the new requirements for nitrogen and ammonia removal. The solution was to upgrade the existing pure activated sludge plant to a hybrid system, with reuse of of the existing basins upgraded to CFAS® process from Biowater Technology and introduce mixing within existing basins.

The plant had originally thirteen basins, being that two pre clarifiers; five sludge tanks and four activated sludge tanks. The upgrade was done by converting two reactors into denitrification reactors, four to CFAS ® reactors; and adapting some of the sludge tanks to activated sludge reactors. The solution was designed for all conditions that permit the removal requirements in two scenarios:

Winter, when the population triples and in the summer. In summer scenario some reactors will be put out of operation, which will reduce the operational costs.

The plant must perform removal of ammonia lower than 5 mg NH4-N/l in any temperature and nitrogen removal of 70% for temperature higher than 12oC.  

The performance of the plant is:


      • 97,7 % COD removal with final effluent with 15 mg/l COD.

      • Ammonia close to 0 mg/l

      • and 82,4% for TN removal with final effluent close to 15 mg/l.

    For questions or more information about this project, please contact Stefan Kjørsvik from Biowater Technology for further questions.