Activated sludge wastewater treatment is based on the action of certain bacterial species.
Thanks to oxygen injected from exterior, such bacteria live and reproduce themselves feeding on organic mass present in the waste water,
and then aggregate in colonies (the so called biomass or sludge flocculation) of specific weight that is higher then water.
At the next stage sedimentation (solid substance from liquid separation) takes place within the tank, so called settling tank,
where the heavy organic solids (biomass) can sediment and the treated surface water collected and sent to discharge.
From the settling tank suspended solids (biomass) are collected and recycled once more.
Since the biomass grows and feeds on pollutants poured into the wastewater treatment plant, their concentration constantly arises.
Therefore, the exceeding biomass is extracted from the process and taken away (for disposal or reuse in agriculture).