Capacity expansion at the St. Lorenzen wastewater treatment plant


History of the sewage treatment plant

The Tobl wastewater treatment plant was built in 1991-1996 and put into operation on 03.07.1996. It has been in continuous operation for 20 years. The treatment plant was originally designed for 135,000 EWbio. In 2011, the deamonification plant was built. With this measure the plant was classified on 150.000 EWbio.

Development of biological population values (EWbio)

In the years 2006 to 2016, the biological population values averaged 114,358 EWbio. In 2017 and 2018, there was a clear increase of 29.28% on average, and we were 4 months above the design of the plant. In addition, a dairy plant is expanding in the next 3-5 years and thus an increase of 22,000 EWbio. can be expected from this plant only. There is a need for action.


Originally, we pursued the idea of equipping line 1 with a membrane bioreactor and thus increasing the plant capacity to 250,000 EWbio. However, this idea was overturned after an economic consideration. It was decided to rebuild the existing deammonification plant and to put line 1 back into operation. Thus, we would reach a plant capacity of 200,000EWbio. and would be prepared for the future for the time being.


The following technical measures were implemented in this project:

  • - 1 new screw compressor with acoustic hood
  • - Electromechanical integration of the screw compressors
  • - Surface aerators and air supply lines
  • - Pumps, mixers and accessories
  • - Reconstruction work deamonification plant
  • - Lime-carbonic acid equilibrium (neutralization reactor)
  • - Electrical integration of the equipment with visualization
  • - New drainage shaft and patented drainage system Demon plant
  • - Sealing of the expansion joints of the basins