The Aquafin water treatment station in Dendermonde (Belgium) handles the water of 72,000 IE (resident equivalents) in the basin of the 'Beneden Schelde'. The water is discharged via a polder canal and pumped into the River Scheldt one kilometre farther on. Built thirty years ago (1985), over the years the WWT plant has been extended and updated with new technologies, relying on Robuschi products in almost every stage of the treatment process. Surely the Robuschi high efficient screw compressors make the difference!
In the Dendermonde water treatment plant, the waste water is pumped from the intermediate elevator gulley of the pre-sedimentation tanks to the central feed culvert of the aeration basins. The waste water is biologically cleaned by the active sedimentation process in the two aeration tanks.
Deep-aeration was opted for the Dendermonde treatment plant and thanks to the injector-aerator it is ensured a very fine air diffusion. Due to the depth of the basin (17 meters), a high water pressure on the bed is obtained so that the bubbles will cover a longer distance. Thus, together with the diffusion of the bubbles, this leads to optimum oxygen absorption. Practically, the plug flow is run continually, so untreated water and return sediment go through different compartments in succession.
In this way, the mixture covers the longest possible distance. The level of the mixed liquid in the aerator arrives below the rim of the overflow gullies, so that the sediment water mixture flows first upwards and then downwards through all compartments. The air feed is intermittent, so that nitrifying and denitrifying processes alternate with one another. Then the water flows to the post-sedimentation tanks.
Three Robuschi Blowers (type S 125/4P, 132 kW each with a capacity of 3,750 m3/h at 750 mbarg service pressure) are also located in the part upgraded in 2005 of the biological water treatment plant. All blowers are controlled by frequency control, according to the oxygen demand of the water basins.