Sludge digestion is one of the most important processes at the wastewater treatment plant in Nijmegen. By expanding the digestion process, a significant increase in biogas and energy production can be achieved. However, this improvement also brings a challenge.

As a consequence of the additional sludge digestion, more nutrients, particularly nitrogen, end up in the effluent, which is then discharged into the surrounding surface water. This surface water is increasingly less capable of processing the structural rise in nutrient concentrations, leading to potential environmental concerns.