The sand trap marks the third step of mechanical cleaning. Fine particles that have passed through the screen are removed here. Such mineral particles including sand, grit and organic matter need to be filtered out as they would otherwise cause excessive wear and tear in the technical installations (pumps and pipes).
As the wastewater is passed into six wide and very deep channels, its flow rate is slowed down to 10 centimetres per second. The length of these channels gives fine particles enough time to settle to the tank bottom. The sand trap scraper pushes the sediment into a hopper, from where it is pumped out. Around 5 tonnes of sandy material is trapped here per day, which is also taken to Wien Energie Fernwärme for disposal.