Membrane bioreactor with gas lift system

Apparatus for treating polluted water, comprising:

• a supply system for polluted water;
• an activated-sludge reactor;
• one or more filter membrane modules;
• an air supply system and a discharge system for discharging permeate passed through the membranes of the modules, wherein the one or more filter membrane modules comprises one or more hollow membranes within a casing in which one or more permeate discharge systems are disposed, wherein the one or more filter membrane modules are adjoined on one side to the activated-sludge reactor and are adjoined on the other side to an air distribution means, and wherein the activated-sludge reactor is connected by means of a bypass line to a sludge receiving container which adjoins the air distribution means and on which there is a discharge line for removing excess sludge mass which settles in said sludge receiving container, in such a way that the water to be treated and air supplied are flowing in the same direction and essentially parallel to the membrane surface through the hollow interior of the membranes, and wherein permeate flowing through the membranes towards a space situated between the casing and the membranes is discharged via the one or more permeate discharge systems.