WWTP of Sofia – close to 100 % self-sufficiency with green energy

Kubratovo wastewater treatment plant treats domestic, industrial wastewater and stormwater entering the sewerage network of Sofia. It was commissioned in 1984 and is now one of the largest in the Balkans.



For 35 years, the facility has operated without interruption. Over the years there have been partial reconstructions and improvements funded by EU funds and Sofiyska Voda`s investment programme.
The plant is located in the lowest northern part of Sofia – Kubratovo, on a total area of 60 ha. Its design capacity is 500 000 m3 of wastewater per day. 


In 2009 a new co-generation system was installed in order to use the biogas and produce renewable energy. The aim was to optimize the operation of the plant and its energy efficiency as well as to reduce carbon emissions.

In 2010 Veolia acquired the majority stake in Sofiyska Voda and put in place new projects for optimization and environmental protection by reusing the waste from its activity. The production of green energy from biogas at the plant continued to increase steadily and in 2014 for the first time since the co-generation system was installed, Sofiyska Voda reached 100% self-sufficiency with green energy.

Since then, the WWTP Kubravovo has remained energy self-sufficient. In 2017, the achieved percentage of energy produced compared to energy consumed was 123%. The capacity of the co-generation installation includes three co-generators, each of them can produce 1063 kW of electricity  and 1088 kW of heating power. 
The next target for Sofiyska Voda is to achieve 100 % self-sufficiency with green energy for the WWTP.


Key figures since the commission of the cogeneration installation in 2009

  • 198 million kWh generated green energy
  • 92 million m3 utilized biogas
  • 1, 080 tons reduced emissions of CO2

The benefits for our client

  • greener city 
  • cost efficiency
  • protecting the environment by recycling waste
  • reduced carbon emissions
  • business to business solutions 
  • provides on-the-job training ground for young engineers

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