In order to be able to sufficiently purify wastewater in a biological treatment plant, a certain nutrient ratio must be present in the wastewater. The main focus here is the so-called C:N:P ratio (carbon:nitrogen:phosphorus). From a biological point of view the optimal C:N:P ratio is between 100:14:3 and 100:10:1.

In municipal wastewater, however, there is a shift towards nitrogen and phosphorus with a ratio of 100:20:5. Due to this imbalance it may be necessary to remove the excess of N and P by means of additional carbon sources for denitrification or precipitants for phosphorus elimination. In the S::Select^® process with aerobic granulated sludge, there is a certain advantage in nitrogen removal, since denitrification can be carried out simultaneously in the granules even during the aeration phase, so that the carbon present is not only available to the aerobic bacteria.


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