Primary Water treatment

At the inlet to the treatment plant the sewage passes through mechanical (coarse) screens with a bar spacing of 10 mm. The screens retain large particles such as paper, plastic, pieces of wood and stones that may cause clogging, wear and tear of the pipes and pumps, or other problems in the following processes. The screens are automatically cleaned, the screenings passed through a compactor and conveyed to a container for disposal. From the screen all flows pass to the aerated grit and grease chamber. The sand and grit which settles here is pumped to a sand dewatering unit and from there to a container for disposal. Grease and oils that inhibit the biological process and cause obnoxious smells, clogging of the pipes, accumulation of sludge and foams in the aeration tanks, are scraped off and collected in a grease pit.

After the grit and grease chamber flows pass through fine screens with 5 mm bar spacing and then on to primary settling tanks. Screenings from the fine screens are handled in a similar way to those from the coarse screens.

In the primary settling tanks, the settlement of large particles is achieved in order to reduce the sewage load on following stages. The organic load can be reduced by up to 20-40 % and the suspended solids by 40-60 %. The settled sludge is pumped to the gravity thickener and subsequently to the digester.