For a small sewage treatment plant without power requirement, cleaning is done in three stages.
The raw wastewater is led into the pre-chamber, where the wastewater is buffered and the suspended solids are sedimented. Primary sludge will sink to the ground and will reduce its volume partially by digestion in the absence of air.
At the outlet of the pre-chamber to the biology reactor, the water is restricted hydraulically and backed up, if required. Independent of any hydraulic peaks, the mechanically cleaned wastewater is distributed evenly over the entire day and forwarded to the biology reactor.