Aerobic biological wastewater treatment in a continuous flow reactor

A method for the purification of substrate-containing wastewater in a continuous flow-through aerobic biologically activated sludge reactor, wherein at least part of biological sludge is conditioned,

• wherein conditioning comprises accumulating sludge particles which have a settling velocity of at least 2 m/h by adjusting the sludge feeding flow rate in an upward-flow or upflow setting such that the faster-settling sludge accumulates at the bottom of a selector, and bringing substrate-containing to-be-purified wastewater, optionally after a pre-treatment step of the supplied wastewater, into contact with the accumulated sludge particles for a contact time of at least 10 minutes in the selector, and wherein the selector works under anaerobic or anoxic conditions, and the selector is operated or designed such that during contacting the sludge with substrate-containing wastewater the sludge residence time in the selector is greater than the hydraulic residence time of the sludge/water mixture in the selector, and
• wherein the conditioned sludge/water mixture leaving the selector, optionally after an additional anaerobic or anoxic contact step, is fed to the aerobic purification reactor and subjected to aerobic treatment,
• wherein the treated wastewater after aerobic treatment is optionally separated from the sludge by settling in a secondary settling tank, flotation or mechanical separation, and
• wherein the selector receives at least a portion of the sludge separated from the aerobically treated wastewater in secondary settling tank, flotation or mechanical separation located downstream from the aerobic purification reactor and/or sludge from the aerobic purification reactor.