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Methane Capture and Combined Energy Production Project  at Wastewater Treatment Plant Kubratovo

The project was implemented on the site of the Sofia wastewater treatment plant near Kubratovo, Municipality of Sofia.
The project objective is the implementation of a system for anaerobic sludge treatment with biogas capture and combustion in the cogeneration installation for the production of thermal and electric power.
The project was initially developed and registered as a joint implementation project (JI) with the support of the European Bank for reconstruction and Development and it was launched on January 1st, 2007. A letter of approval was received for the project from the ministry of Environment and Water dated 1 August 2007 . A declaration for approval dated 10 July 2007 was also issued by the Ministry of Economy of the Kingdom of the Netherlands .

Notification for public discussion

The project was also registered in UNFCCC, Procedure 1 with identification number BG1000166 (More Information).
The following general measures were implemented in order to achieve the project objectives and to comply with the EU Directives for wastewater and treatment of sludge from wastewater: 

  • Primary settling tanks

The renewed bioreactors are supplied with mixed sludge from the primary settling tanks and the secondary sludge (surplus activated sludge) from the facility for biological treatment, and then they are pumped in the bioreactor.

  • Bioreactors for anaerobic sludge treatment

The installation for sludge anaerobic treatment stabilizes the sludge. With this procedure the organic matter of the sludge is reduced, which also helps to reduce the dry matter from the total sludge. This process has a positive impact on dimensioning the units for sludge treatment after the bioreactor and also for sludge dewatering and odour elimination.
After the completion of the process of decomposition of sludge, it is dewatered and used as a soil enricher.

  • Raw sludge pumping station

Five new raw sludge pumps were installed in the existing pumping station as part of the project.

  • Sludge circulation system

In order to reheat the raw sludge and maintain the temperature of the process under mesophilic conditions (35°C), a new system for combined sludge circulation and heating was installed in the basement of the new servicing building. 6 centrifugal pumps for dry installation were installed and four pumps are in operation and two are on stand-by regime for urgent cases.

In order to reheat the raw sludge and maintain the temperature of the process under mesophilic conditions (35°C), a new system for combined sludge circulation and heating was installed in the basement of the new servicing building. 6 centrifugal pumps for dry installation were installed and four pumps are in operation and two are on stand-by regime for urgent cases.
  • Heat exchanger

The anaerobic process is realized under mesophilic conditions, which means in temperature variation between 33 and 37°С. The fresh inflowing raw sludge has to be heated up until reaching the needed temperature conditions. Also, the loss of heat of the bioreactor should be compensated. For this purpose a heat exchanger for each bioreactor was installed.
The methane obtained in the wastewater treatment plant is captured in a gas holder, serving as a buffer, and then it is supplied to the cogeneration modules, which on their part decrease the electric power purchased from the grid and also the diesel fuel used for heating. In case of excess of electric power, it is transferred to the transmission network.

The project has been implemented at two stages:  

The anaerobic process is realized under mesophilic conditions, which means in temperature variation between 33 and 37°С. The fresh inflowing raw sludge has to be heated up until reaching the needed temperature conditions. Also, the loss of heat of the bioreactor should be compensated. For this purpose a heat exchanger for each bioreactor was installed.The methane obtained in the wastewater treatment plant is captured in a gas holder, serving as a buffer, and then it is supplied to the cogeneration modules, which on their part decrease the electric power purchased from the grid and also the diesel fuel used for heating. In case of excess of electric power, it is transferred to the transmission network.

Construction of a new bioreactor system, consisting of four bioreactors, 7000 m3 each. Also, a flare incineration system for methane was installed, consisting of 2 х DN150 flares.

Construction of three new cogeneration modules GE JMS 320 GS-B.LC, each with electric power of 1063 kW and thermal power of 1088 kW, for the production of electric and thermal power at the biogas incineration. 

Since 1 January 2007 the bioreactors, constructed under the project, have been in operation. During the first period of the Kyoto Protocol (01.01.2008 – 31.12.2012) the project passed four verifications and reduction emission units were issued (ERU) equal to a total of 403,796 tCO2e.

The validity the Kyoto Protocol expired on 31 December 2012 and the amendments to the Protocol of the Doha meeting of the parties have not been enforced yet. Therefore, the Company made a decision to register the project for methane capture and recovery in the wastewater treatment in Kubratovo in the voluntary Gold Standard, which will allow revenue resulting from emission reduction. The expected reduction of greenhouse gas emissions under the project after its registration under the God Standard is 56,747 tCO2e per annum. It will be possible in the future to claim with the project for voluntary carbon credits (verified emission reductions - VER) and trade them at the voluntary market. 

Public discussion report

Comments and recommendations regarding the subject of the public discussion held can be sent to the e-mail address stated at the bottom of the page:
E-mail:
goldstandard@sofiyskavoda.bg

Telephone: 02/ 8122 530

Contact person: Jelyaz Rangelov – Wastewater treatment senior manager

For details on The Gold Standard Foundation please refer to info@goldstandard.org

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