At the beginning of wastewater treatment, large solid particles are fished out of the water with rakes.
The second basin is called sand trap, because here small particles like sand grains are separated from the wastewater. This works by keeping the water completely still and waiting until the sand grains have sunk to the bottom.
In the next basin, other debris are removed. This time from the surface of the water, so all the particles which are swimming.
In the aeration tank there are really small creatures, the bacteria and also fungi. These eat whatever dirt is left in the wastewater, making the water clean.
This is where the little critters are separated back out of the water so it's nice and clean. This also works by waiting until they have sunk to the bottom.
The clean water is discharged into the river or into a lake.
All the sludge from the wastewater is collected in these towers. The sludge can then be turned into gas, which is used as energy. In the end, the sludge contains important nutrients like phosphate.