Upgrade and extension of Warsaw WWTP, Poland

Solution to which problem

In 2004, when Poland joined European Union, Warsaw wastewater treatment plant was not in line with European standards. The main driver on the extensive modernization project was the need to meet EU wastewater standards, including limits on nitrogen of 10 mg/l and 1 mg/l for phosphorus, and to provide adequate treatment for all urban effluent flows. 

Technical conditions

Warsaw WWTP is designed for a population of around 2.1 million PE, the extension and modernisation of this plant has helped to more than double its former 200 000 m³/day inflow treatment capacity to routinely deal with a daily inflow of 450 000 m³, rising to a potential inflow of 515 000 m³/day at peak times.

The upgrading consisted of: install 30 kilometers of wastewater collection system; construct a tunnel and a siphon under the Vistula River to transport the left bank effluent; rebuild, modernize and extend the existing treatment plant; and build a sludge incineration plant.


At Czajka wastewater treatment plant, Warsaw, 192 tons of sewage sludge is produced daily. The treatment is based on the active sludge principle. This technology was chosen for its reliable and solid treatment and service.

The wastewater is settled and treated biologically to remove the carbon, phosphate and nitrogen. The biological treatment is managed using advanced controls enabling a high level of treatment performance, while saving energy and reagent consumption. It is Veolia’s Bio-denitro process that achieves high levels of nitrogen removal. Odors are treated using the Veolia’s air treatment process, Aquilair.

The sludge treatment takes place in 4 newly constructed, as well as 6 reconstructed digesters. The biogas generated is cleaned and desulphurised and then stored in biogas storage tanks. The biogas is directly used for power and heat generation. The fermented and sterilized sludge is loaded into an intermediate storage container, after which it is mechanically dewatered before it is finally transported to the newly constructed sludge incineration plant.

Once the wastewater has been treated, the sludge from the Czajka wastewater treatment plant, as well as that from Poludnie, Warsaw’s other wastewater plant, is incinerated in a furnace at 850°C. The incineration plant uses the Pyrofluid thermal treatment process that oxidizes the organic matter leaving recoverable ash and energy.


The plant treats 600 metric tons of sludge a day. The incineration plant also uses the sludge’s inherent heat to generate green energy. At the end of the treatment process, 90% of the sludge has disappeared and the remaining 10% is recovered.

According to the director of infrastructure of the City of Warsaw, recycling at Czajka truly works: for example, 30% of the energy needed annually by street lighting in Warsaw can be obtained by using biogas generated through digestion. Annually, this corresponds to 140 train cars of coal.

The construction of the WWTP Czajka is considered to be one of the most important environmental protection measures in Europe. The project has improved substantially the water quality of the Vistula River, and consequently that of the Baltic Sea.

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