These micropollutants or trace substances have been shown to have significant consequences for the environment. For example, certain beta blockers, anti-epileptic drugs and contraceptives cause damage and changes to the organs, sexual characteristics and behavior of fish if they get into the water. Scientists are currently studying how they damage the human organism.
For the most part, microplastics measuring five micrometers to five millimeters and trace substances can only be removed in a fourth purification stage. This is achieved by adding activated carbon powder to the water in a contact tank. The activated carbon with its porous and brittle structure has a large internal surface area. In physical terms, one teaspoon of activated carbon powder has the same surface area as a football pitch. This surface area provides lots of room for the trace substances to accumulate. The activated-carbon-enriched water is therefore kept in the contact tank for 15 to 20 minutes. In conventional plants a further tank, called a sedimentation tank, is required to remove the activated carbon from the water after this purification process. The activated carbon falls to the bottom of the tank and, together with the attached trace substances, is later separated with the sewage sludge and burned. Apart from the contact tank for activated carbon treatment, a bigger investment in a large sedimentation tank that takes up a disproportionately large amount of space is also required. Measurements have revealed that this method removes 80 per cent of the pharmaceutical residues and X-ray contrast agents from the wastewater. Wastewater treatment plants without this fourth purification stage only hold back around 30 per cent of the trace substances collected.