Opening of renovated Kubratovo sewage treatment plant

The largest sewage treatment plant in the Balkans, Kubratovo near Sofia in Bulgaria, was officially opened on 13 June. Tauw supervised the design and construction process for this project and carried out the project management. At the end of 2008 Tauw was commissioned, together with HPC, to carry out this 1.3 million euro project.

The plant was formally opened by Bulgaria’s Prime Minister, the minister and junior minister for the environment and water, the Dutch ambassador in Bulgaria, the mayor of Sofia and the local manager of Veolia.
The prime minister, whose birthday it was on that day, was presented with a fish bowl containing two fish as a gift by Sofijska Voda (part of Veolia and plant manager). The fish had been caught in the purified waste water.

The costs for the renovation of the sewage treatment plant amounted to over 22 million euros. The improved effluent quality means that the water in the river Iskar, which flows into the Danube, is a lot cleaner.


The renovations at the Kubratovo sewage treatment plant mainly consisted of:

  • Increasing the biological capacity from 1,000,000 p.e. to 1,800,000 p.e. (at 136 g TOD/d)
  • Introduction of nitrogen and phosphate removal to meet the EU effluent requirements. The existing activated sludge tanks have been completely overhauled for this purpose and equipped with various zones for biological phosphate removal, nitrification and denitrification. In addition, two new final settling tanks, a return sludge pumping station and a dose-measuring device for chemicals have been constructed
  • Renovation of primary and secondary sedimentation tanks

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