The challenge
The main challenge before the team of Sofia wastewater treatment plant (WWTP) is to treat the wastewater of Sofia and discharge it clean into nature.
Sofia WWTP is fully energy self-sufficient since 2015 and the next challenge is to achieve full energy neutrality for the entire water and wastewater cycle of Sofia municipality.
Last but not least, the sludge produced from the treatment of the wastewater is successfully utilized as a fertilizer in agriculture.
Veolia’s solution
Sofia WWTP treats wastewater from domestic and industrial users as well as rainwater from the combined sewerage network of Sofia. It has a design capacity of 1.5 million people and treats more than 480 000 m3 of domestic and industrial wastewater daily in line with the most stringent EU requirements (including nitrogen and phosphorus removal).
The plant was commissioned in 1984 and is one of the largest in the Balkans. Historically it has consumed between 16 000 and 24,000 MWh of electricity per annum.
Following the installation of CHP units in 2009 the green energy produced at the WWTP increased from 1500 MWh to over 23 600 MWh in 2021.
The measures implemented to reduce the energy consumption of the WWTP led to an excess of 2 541 MWh in 2023, i.e. the plant produced 12 % green energy in excess to what was needed for its operation.
This progress was achieved through targeted initiatives, particularly in 2017, when the company commissioned new frequency-regulated air blowers for the biological treatment step, which increased the efficiency of the process by 25%.
In parallel, a project for utilizing exhaust heat from the CHP installation was implemented and it added 570 kW to the installed capacity, which has been of great importance as an additional heat source to increase the temperature of the anaerobic digesters. This project has resulted in a 13% increase in the energy produced on site.
Key figures since the commissioning of the cogeneration installation in 2010 until the end of 2023:
- 278 million kWh generated green energy
- 142 million Nm3 utilized biogas
- 990 K tons reduced CO2 emissions
- 1 million tons of sludge utilized in agriculture
Sofia, Bulgaria
Duration: contract started in 2000 and expires in 2034
Type: Concession
>131 М cub.m. p.a. of treated wastewater discharged in the Iskar river
112 % Energy self-sufficiency
The benefits
- Thanks to the continuous work of Sofia WWTP each year over 131 million m3 of treated wastewater discharged into the Iskar river.
- The production of green energy fully covers the energy needs of the facility.
- Avoiding over 70 000 tons of carbon emissions per annum.
- Nearly 85% of the full water cycle energy demand is covered by the green energy produced at Kubratovo WWTP in 2023
- Sofiyska Voda JSC aims to become 100% energy neutral by 2025
REGIONS & CITIES
Greener city
Cost efficiency
PLANET
Over 131 M m3 treated wastewater returned to nature
Reduced carbon emissions
Protecting the environment by sludge waste
WOMEN & MEN
Provides on-the-job training ground for young engineers