Patent ID: 7175764

Claim:
A method to purify wastewaters comprising the steps of: a) aerobic clarification of the wastewater by activated sludge in an activation stage; b) subsequent clarification of a portion of the wastewater/activated sludge mixture, exiting from the activation stage; c) dehydration in a dehydrating unit comprising a sieve belt filter of another portion of the wastewater/activated sludge mixture exiting from the activation stage; d) returning at least a portion of the activated sludge separated in step b) to the activation stage; and e) guiding the purified wastewater directly from the dehydration step c) to an output, wherein in step e) the activated sludge separated in step b) is returned to the activation stage with a concentration of about 2.5 g/L to about 7 g/L and the activated sludge separated in step c) is returned to the activation stage with a concentration of about 30 g/L to about 60 g/L.