Submerged membrane bioreactor for treatment of nitrogen containing water

A membrane bioreactor (10) having:

• (a) a tank (12) containing mixed liquor (15);
• (b) filtering membranes (22) immersed in the mixed liquor (15) and having permeate sides (20) in fluid communication with the mixed liquor (15) only through the membranes;
• (c) a source of suction (23) on the permeate side (20) of the membranes (22) to withdraw filtered permeate (26) through the membranes (22);
• and,
• (d) a scouring bubble supply (30) to provide scouring bubbles (32) below the membranes to inhibit fouling of the membranes,
• characterized by
• (i) an oxygenating bubble supply (47) operable to intermittently provide bubbles (50) containing oxygen in the mixed liquor (15) wherein the mixed liquor 15 is converted from an anoxic or anaerobic condition to an aerobic condition;
• (ii) a sensor (60) to provide a signal indicating the level of oxygen reduction potential or dissolved oxygen concentration of the mixed liquor (15);
• and,
• (iii) a programable logic controller (62) operable to receive the signal from the sensor (60) and programmed to turn the oxygenating bubble supply (47) on and off repeatedly so as to alternately create primarily anoxic and primarily aerobic conditions in a selected portion of the mixed liquor (15) and to consider the signal from the sensor in determining when to turn the oxygenating bubble supply (47) both on and off.