Wastewater from Vienna‘s households, commercial and industrial establishments and also stormwater flows from the sewer into the main wastewater treatment plant - 680,000 m³ a day during low flow (dry weather), and 1,550,000 m³ a day during heavy rainfalls. The grit chamber is the first installation of the mechanical cleaning stage. A depression in the sewer floor causes coarse solids such as gravel and grit to settle to the bottom. This is extremely important as it helps to protect downstream installations, such as the Screw pump facilityScrew pump facility and the screening plant, from damage. Once a week one of the channels is shut off, emptied by pumping and the coarse solids are dug out by a clamshell. The dug-out material is loaded into containers and taken to Wien Energie for disposal.