In 2021 Sofiyska Voda, operated by Veolia, completed the construction and commissioned a new digester, thus increasing by 25% the capacity for green energy production in the treatment of the capital’s wastewater.  The capacity of the digester is 7,000 m3 (as much as 3 swimming pools) and it is designed in line with the most modern technologies. Reliable sludge fermentation is guaranteed with that addition to the technological process, and higher volumes of biogas are expected, respectively. The processed sludge will have better parameters – less odor and organic matter, as well as it will be more compact in size. 

The main function of the plant near Kubratovo is to treat the wastewater of the city with a population of more than one million and return the water to the Iskar River with qualities identical to those of the pure river water. Along with that process, electric and heat energy is produced through stabilization of the sludge derived from the inflowing water. The sludge separated from the water through naturally-occurring processes, though speeded up by the plant facilities, reaches the digesters where the digestion takes place. During that process biogas – methane is released. The methane, which if released into the atmosphere causes a greenhouse effect, here is converted into electricity and heat energy through co-generation. After the sludge is stabilized in the digester, it is dewatered and consequently donated to farms to serve as a fertilizer for certain types of crops. The obtained fertilizer is rich in phosphorus and nitrogen and is favorable for their raising. The result is a completely closed green energy loop with no waste. 

The digester is part of the investment program of Sofiyska Voda, operated by Veolia, from the past regulatory period 2017 – 2021. The company invested BGN 6 M, thus turning it into one of the first examples of green energy transition and circular economy in Bulgaria.  

The facility was opened by the Executive Director of Sofiyska Voda - Vasil Trenev and the Country Director of Veolia for Bulgaria – Francois Debergh. “We commissioned the digester at a time, when a lot is being said about the high price of natural gas and electricity or their shortage. The electricity generated here is sufficient to meet the energy needs of the plant and the plant is 100% energy independent. We even produce more than we consume at the plant. Naturally, our dream is for the entire Sofiyska Voda, operated by Veolia, to become energy neutral and it is one of the steps on the path we pursue. Our next plans are related to the construction of one more cogenerator – we have three at the moment. In this respect, fortunately, the company has not been affected by crisis with the electricity prices like many water operators and also the whole of Europe”, Trenev explained.

Like all companies of the Veolia group worldwide, Sofiyska Voda is implementing the Group Purpose aligned with the United Nations Sustainable Development Goals, namely - ecological transformation. The Purpose is our compass in our daily activities. The core of it is to conduct the necessary ecological transformation we need at global scale. 

We want to be useful not only to the planet, but to our stakeholders, as well. We do believe we are useful to Sofia and we have for Bulgaria and its Capital the aim to continue increasing our positive impact and improve continuously our services while serious challenges are ahead of us as a society. For our partner - the municipality of Sofia, we promote worldwide the capital City with this circular economy flagship and highlight the efforts of Sofia to become greener, more resilient and more sustainable, Mr. Debergh stated. 

Deputy Mayor for Finance stated that the new digester was one of the important investments in the capital. “On the one side, it is an ecological project as methane is one of the most aggressive greenhouse gases. On the other hand, resource recovery is implemented and in this case, Sofiyska Voda manages to use the methane for the generation of electricity. At the moment, we are all talking about renewable energy sources and how in the coming years their share in the energy sector of the country must increase and here it is being done. I think that it is an extremely good example and I hope that it will happen at other places, as well.” Barbalov added.

Another innovative solution of Veolia – Hubgrade- is also located in the WWTP near Kubratovo. It is a patented monitoring smart system in Veolia’s control centers. The system allows remote supervision and control of the facilities and processes in real time, thus contributing significantly to the optimization of the energy costs and the current costs of chemicals. On the other hand, the efficiency of the processes and facilities is enhanced as well as the control over the various units. 

At the same time, while the plant produces green energy for the needs of our treatment plant, more than 61 thousand tons of СО2 emissions are saved annually. In 2014 Sofiyska Voda received the first Gold Standard certificate for this project and in 2021 it renewed the certificate according to the latest requirements of the Gold Standard with a focus on the contribution of the project to the achievement of the UN Sustainable Development Goals. 

With the implementation of this closed-loop production cycle, in the past year the wastewater treatment plant in Sofia was at the top of world efficiency rankings and is a convincing real-life example of a circular economy.  

The WWTP in Kubratovo near Sofia processes more than 350,000 m3 of wastewater a day and more than 130 million m3 a year. Thus, for over 30 years of existence the plant has processed in total more than 4 billion m3 of wastewater, or nearly 8 full volumes of the main water source of Sofia – the Iskar dam.