TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Process: The two discrete modes of operation differ from each other in relation to backwashing regimen, permeation regimen, air scouring regimen, membrane chemical cleaning regimen, and/or sludge filterability enhancement regimen. The two discrete modes of operation differ in the ratio of time in which the membranes are air scoured relative the time in which the membranes are not air scoured. Changes in mode of operation are made following a hierarchy of available process changes. The process include comparing value(s) of parameters with at least one of a set of two reference values associated with each of the values being compared. The two reference values include a higher value and a lower value, and the mode of operation is changed when value(s) of parameters is above its associated higher reference value or below its associated lower reference value.Preferred Parameters: The parameters include adsorptive fouling resistance, cake resistance, and/or a change over time in total resistance after backwash. The length of time that gas flows at the second rate does not exceed 60 seconds or is continuously for greater than or equal to5 minutes or during a time other than a time near or in which the membrane unit is backwashed. The length of time that gas flows at the higher rate is continuous and does not exceed 20 seconds or may exceed 20 seconds but occurs every less than or equal to5 minutes frequently or at a time near or in which the membrane unit is backwashed.    TECHNOLOGY FOCUS - COMPUTING AND CONTROL - Preferred Process: Operation of the immersed membrane filtration system is altered considering real-time process information with feedback control. The operation of the system is altered according to selecting the on and off aeration time during cyclic or intermittent aeration cycle, selecting the on and off production time for an individual train, and/or selecting the number of trains in operation and design permeate flow for each train as part of a complete system. The feedback control is manual, i.e. plant operator receives information from a control system and manually adjusts the air supply equipment to deliver the correct flow or manually sets on/off aeration times, on/off production times, or trains in operation and permeate flows. The process is altered by altering its aeration frequency factor.Preferred Information: The process information includes permeate flow, reject or concentrate flowrate, sludge filterability, fluid temperature, fluid viscosity, fluid suspended solids concentration, coagulant or other pretreatment chemical addition rate, activated carbon dosage rate or concentration, blower inlet air temperature, recovery rate (permeate produced/feedwater provided), dissolved oxygen concentration, oxygen uptake rate, solids retention time, and/or mixed liquor recirculation rates. The process information is used to calculate a resistance value.