INSTALLATION FOR BIOLOGICAL TREATMENT AT HAN BOGROV SITE

Biological treatment plant at “Han Bogrov” site

The plant for biological treatment at “Han Bogrov” site has been constructed as part of the “Integrated system of facilities for treatment of solid waste of Sofia municipality” project. The project is funded by the Operational Programme “Environment 2007-2013”, co-funded by the European Regional Development Fund and the Cohesion Fund of the European Community. The project aims at building a modern, integrated waste management system for solid waste of the city of Sofia.

Contracting authority of the project: Sofia Municipality

Designer and Contractor of the project: “EGGERSMANN & CO” Consortium

Consultant (Construction supervision) - conducted by “IGIP - CEG - ICEPE - HIS /ICIH/” Joint venture.

“Han Bogrov” site is located in the area of “Malo livade”, a land of the village of Gorni Bogrov, Kremikovtsi district. Transport accessibility of “Han Bogrov” site is provided by the provincial road Sofia - Elin Pelin.

A total of 26 buildings and facilities are located at “Han Bogrov” site. In compliance with the project of the plant, the following development indicators have been implemented:

The biological treatment plant is designed to receive and process 44 000 tons a year separately collected bio-waste at the territory of Sofia Municipality.

The facility operates as two separate production lines - for the treatment of 24 000 tons / year green waste and 20 000 tons / year bio-waste from households and commercial facilities in the city of Sofia.

A. Plant for treatment of green waste

The “green” waste received at the plant from the maintenance of the green system of the city is stored at an open site. The material undergoes pre-treatment, including the removal of undesired impurities and shredding, in order to obtain the appropriate for the process homogeneous structure. The prepared material is loaded in composting cells (tunnels), where the first phase of intensive composting takes place for a period of two weeks.

The process is optimized by adjusting and harmonizing of the parameters temperature, humidity and ventilation. The technological process is fully automated, cost-effective and with high performance.

Number of tunnels	4
Dimensions of the tunnels	25/7/5 m
Capacity	231Mg
Residential time	2 weeks
Filling height	2,93 m

Following the completion of the intensive composting, the material is transferred to the area of ​​compost maturation, where located in composting lines, it is mixed and sprayed on a weekly basis with a windrow turner, thus achieving the necessary aeration and the optimal humidity. This process lasts for 6 to 8 weeks. At the end of the maturation, the compost has a IV-V level of maturity according to the compost quality standard RAL GZ 251 Bundesgütegemeinschaft Kompost, Germany. During the maturation of the compost material no emissions are present. After completion of the second phase of composting, the matured compost undergoes fine screening through a drum screen where the fine fraction is the finished product, and the coarse fraction is returned as a structural material. Composting is based on bio-chemical processes carried out by microorganisms, which turn the organic material into humus. The quality compost is a great alternative for a fertile soil recovery.

Exhausted air from premises is used for aeration in the composting tunnels and then, going through a humidifier and a bio-filter, it is released purified into the atmosphere. In the composting cells a damping system is also provided that optimizes the moisture content of the compost material upon incoming of dry waste. For waste with low water content a further humidification is necessary during the composting process. The lead of excess water is conducted through the Spigot system. Therefrom it goes to а leachate tank. Collected water will be transported by a mobile tank for purification in the Wastewater treatment plant (WWTP) at “Sadinata” site.

Current data for the controlled technological parameters are transferred, processed and managed by an automated system - SKADA. Management is located in the central control room.

The green waste treatment plant is equipped with internal power installations in the buildings and for the facilities, site lighting, grounding systems and lightning protection systems.

B. Plant for treatment of bio waste

The separately collected bio-waste from commercial facilities and households undergoes a pre-treatment in two separate functional areas, in accordance with the specifics of the incoming waste, where impurities from packaging, metals and others are removed. The organic material is treated to form a suspension, which is led to the anaerobic treatment zone. The fermentation process is conducted in a bio-reactor at 37 ° C, which results in the formation of bio-gas and partially stabilized fermentation product. The system for bio-gas collects and analyzes the bio-gas and after its purification and drying, the methane is burned in two combined thermal and electric units (KTEA) with electric power 255 kW and 600 kW. There are two facilities with different power selected as the generated gas in the bioreactor can be with variable flow rate. Practically, the two facilities may operate separately or jointly, so that an optimum regime of utilization of the biogas is achieved. The facility is equipped with an independent system for burning excessive amounts of biogas - a torch for closed combustion of methane in an emergency shutdown of the generators or irregular gas flow.

The generated electricity is fed into the electric distribution network, and the thermal energy is used for technological needs by different users at the site. The partially stabilized fermentation product is sanitized by pasteurisation at 70 ° C, and then dried, in order to prepare for subsequent process of anaerobic treatment. The excess process water is led into a tank for drainage and therefrom in a wastewater tank. Wastewater from the site is transported to the WWTP for treatment – “Sadinata” landfill. The dewatered solid material is led for composting. A structural material is added to it, that is made homogenous and then loaded in the corresponding composting cells. Due to the low biological activity of the material, an additional heating of the material is conducted in the compost cells which supports the process of intensive maturation. The residence time is about 3 weeks, after which the compost undergoes a fine processing. Due to the specifics of the bio-waste, this processing is more precise and involves passing through a drum sieve and a separation module (densimetric table), where the unnecessary impurities are removed. The result is fine and coarse fractions, where the fine fraction is the finished product, and the coarse fraction is returned as a structural material. The exhausted air from the premises is pre-heated and is used for aeration in the composting cells, and then purified by the ammonia in the acid scrubber. The product of this process is ammonium sulfate, which can be used in agriculture as a fertilizer. After the acid scrubber, the air passes through a bio-filter and is exhaled purified into the atmosphere. Current data for the controlled technological parameters are transferred, processed and managed by an automated system - SKADA. Management is located in the central control room. The bio-waste treatment plant is equipped with internal power installations in the buildings and for the facilities, site lighting, grounding systems and lightning protection systems.

At full load the plant generates 13,000 tons of compost, more than 600 MWh electricity and about thirty tons of ammonium sulfate per year.

The halls, where the equipment is located, are built with prefabricated reinforced concrete structure, lined with PUR panels. The floors are made of polished, fiber reinforced concrete, with thickness of 20 cm, smoothed with laser instruments for level control.

The entrance to the site is an existing road III-105 - Sofia - Elin Pelin. There are two entries - exits provided, one with a width of 10 meters and an emergency one - with width of 5 m. The site is accessible from the main entrance for cars. After verification at the checkpoint, the flow is divided in two - one direct passing and one for passing through the scale. The traffic in the area of the site is regulated by road marking.

The spatial development set out in the project has been implemented. For better isolation from the surrounding areas and the transformation of the plant in an environmentally friendly area, green belts of coniferous and deciduous trees have been planted.

The property on which the installation is located is surrounded by a solid fence along the entire perimeter. A system for video surveillance is implemented throughout the site.

The water supply at the site is implemented through an external connection for potable water. The technological needs of water in the plant have been met through collecting and filtering of rain water as well as through its own source - drill well, through the constructed and operational technological water-conduit. In order to meet fire protection (FP) needs, a fire protection tank and fire protection water pipe have been constructed. There are sewerage networks for domestic wastewater, drainage, site rainwater and rooftop rainwater. Wastewater from the site is transported to the WWTP for treatment at “Sadinata” site.

Administrative building is a solid two-storey concrete building. The building is glazed with PVC windows and the front walls are heat-insulated with 8 cm - EPS, with a plaster on a polymer net. The building is equipped with a wheelchair ramp, providing access to the first floor, and the second floor is equipped with a robotic facility for access of disabled persons. The first floor is equipped with a toilet for disabled persons.

Heating is provided through water heaters, powered by a heat exchanger that uses residual heat from the area of ​​anaerobic composting of bio-waste. In case of shortage of heat, a pellet boiler is provided.

The facility is unique in Bulgaria and since its putting into operation at the end of 2013, Sofia Municipality has the capacity to utilize the bio-waste of the city in a modern and environmentally friendly way.