Abstract: A process for the treatment of wastewater is disclosed, which comprises (a) contacting the wastewater with fast settling sludge from step (c) in an anaerobic zone, obtaining a mixture of wastewater and sludge; (b) subjecting the mixture from step (a) and slow settling sludge from step (c) to an aerobic zone, obtaining a water and sludge mixture; (c) subjecting a first part of the mixture from step (b) to a sludge selection step, wherein sludge is selected based on settling velocity and a first portion containing slow settling sludge and a second portion containing fast settling sludge are collected, wherein average settling velocity of the fast settling sludge is greater than that of the slow settling sludge, and wherein the first portion is returned to step (b) and the second portion is returned to step (a); and (d) separating sludge from a second part of the mixture from step (b).

Abstract: A process for the treatment of wastewater is disclosed, which comprises (a) contacting the wastewater with fast settling sludge from step (c) in an anaerobic zone, obtaining a mixture of wastewater and sludge; (b) subjecting the mixture from step (a) and slow settling sludge from step (c) to an aerobic zone, obtaining a water and sludge mixture; (c) subjecting a first part of the mixture from step (b) to a sludge selection step, wherein sludge is selected based on settling velocity and a first portion containing slow settling sludge and a second portion containing fast settling sludge are collected, wherein average settling velocity of the fast settling sludge is greater than that of the slow settling sludge, and wherein the first portion is returned to step (b) and the second portion is returned to step (a); and (d) separating sludge from a second part of the mixture from step (b).