Recovery of generated sewage sludge
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 30 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 98% self-sufficiency with green energy. 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.

Resources needed

The approximate amount of resources invested for modernization in current good practice is 49,08 mln. euro provided by the EU funds as well as investments by the company`s investment programme.

Evidence of success

Key figures: 19 M kWh of green energy produced in 2014 networks; 10.6 M Nm3 biogas utilized in 2014; 728 000 t CO2e reduced emissions since the installation of CHPs in 2009.

Difficulties encountered

Economics –The long rate of investment return.

Potential for learning or transfer

The next target for Sofiyska Voda is to achieve 100 % self-sufficiency with green energy for the WWTP. The potential of good practice transfer is highly appreciated in the current programing period of OP Environment 2014-2020 and OP Innovations and Competitiveness 2014-2020, where circular economy and resource efficiency project, were promoted. The Bulgarian entities can apply for financial support of measures directly related to resource efficiency and circular economy, waste preventions and recycling. The current good practice and the available financial support, provides practical opportunities for learning or transfer.
You can find relative good practices on CircE Web site: Synpotic opportunities report and the Opportunities reports, etc.
Learning and/or transfer inspiration can be taken from all these quoted GPs, as well as from the current one.
Main institution
Sofiyska voda
Югозападен, Bulgaria (България)
Start Date
October 2009
End Date


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