The first step in wastewater treatment is mechanical cleaning. This is realized by rakes. The rakes are used to separate solids from the wastewater.
In the sand trap, the wastewater is cleaned of smaller solids. This is done by bringing it to rest and sedimenting small solids such as sand.
The primary clarifier is used to further separate various substances. Particles lighter than water are drawn off at the surface and heavier particles sediment here as well.
The aeration basin is the actual clarifier. There, bacteria and fungi metabolize the organic components, breaking them down into their component parts.
In the secondary clarifier, bacteria and other remaining components are again separated from the clean water by sedimentation.
The treated water is returned to the natural water cycle by being discharged into a river or other natural body of water.
In the digesters, the sedimented bacteria and sewage sludge are partly processed into gas. This is used to supply energy in many wastewater treatment plants. In the end, the sewage sludge still contains important resources, such as phosphate, which unfortunately cannot be recovered economically at present, if at all.