Municipal and industrial wastewater and rainwater from the municipalities of Domžale, Kamnik, Mengeš, Trzin, Komenda, and Cerklje na Gorenjskem flows through the sewerage system into the Domžale-Kamnik Central Wastewater Treatment Plant where it is cleansed and from where it then flows into the Kamniška Bistrica river. The wastewater treatment plant receives wastewater from all the households connected to the wastewater system and from all large industrial sources. The capacity of the plant is 149,000 PE.
At the CČN, wastewater treatment is carried out in three stages. First, there is the mechanical stage, during which coarse solids and large debris are removed from wastewater. Then follows the aerobic biological stage, during which carbon, nitrogen and phosphorus compounds are removed. The third stage is the anaerobic biological digestion, during which sludge is converted into biogas and digested sludge.
The ČCN can receive up to 9 million cubic metres of wastewater per year. In compliance with the environmental permit, it can also receive septic tank sludge, sludge from small wastewater treatment plants, and liquid waste. The plant produces approximately 4,000 tons of waste sludge and approximately 3 million kilowatt hours of electricity annually.
All technological treatment processes are automated and under constant control. Regular measurements and monitoring of wastewater make sure the treated water at the outflow is suitable for discharge into the river and the measured quality parameters are below the permitted limit values, i.e. less than 70 milligrams per litre for chemical oxygen demand, less than 15 milligrams per litre of biochemical oxygen demand, less than 10 milligrams per litre of total nitrogen, less than 1 milligram per litre of total phosphorus, and less than 25 milligrams per litre of suspended solids.
The wastewater treatment plant operates in such a way that its emission influence on water and soil, air and noise connected with its operation is within the legal limits.
From 2014 to 2016 the plant upgrade was carried out to add the processes for nitrogen and phosphorus compounds removal.