Abstract: A membrane bioreactor uses a process and apparatus for dosing flux enhancing chemicals (FEC) to respond to temporary periods of operation that cause, or are likely to cause, membrane fouling. An FEC dosing device is provided in communication with a channel separating a process tank and the membrane unit of an MBR. A mixer in the channel rapidly mixes dosed FEC with mixed liquor flowing into the membrane tank. The dosing device is connected to sensors sensing conditions in the channel, the membrane unit or both. FEC is added to the mixed liquor flowing into the membrane unit considering conditions in the mixed liquor flowing to the membrane unit or membrane operating parameters or both. The FEC dosage may be in the range of 0.05 to 10 mg/g MLSS. The process may include steps of initiating dosing, adjusting the dosing concentration, and terminating dosing.