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A membrane filtration system comprising one or more submerged ultrafiltration or microfiltration membrane assemblies at ambient pressure, with mixed liquor is discharged underneath each membrane assembly. In a sequenced batch reactor system, a coarse bubble air diffuser for scouring each membrane as

A membrane filtration system comprising one or more submerged ultrafiltration or microfiltration membrane assemblies at ambient pressure, with mixed liquor is discharged underneath each membrane assembly. In a sequenced batch reactor system, a coarse bubble air diffuser for scouring each membrane assembly is supplied with air only during the backwash cycle of the filtration system and not during the filtration cycle. In a membrane bioreactor system, the biological treatment section is physically separated from the filtration section and fine bubble air diffusion is used in the biological treatment section.

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What is claimed: 1. A process for treating effluent in a sequenced membrane batch reactor (SMBR) comprising; (a) providing a sequenced batch reactor having a biological section and a membrane filtration section; (b) treating the effluent in the biological section by (i) passing the effluent continu

What is claimed: 1. A process for treating effluent in a sequenced membrane batch reactor (SMBR) comprising; (a) providing a sequenced batch reactor having a biological section and a membrane filtration section; (b) treating the effluent in the biological section by (i) passing the effluent continuously into a biological treatment tank provided with at least one transverse baffle across the tank; (ii) dividing the tank into a first portion adjacent the inlet and a second portion remote from the inlet, wherein the volume ratio of the first portion to the second portion is between 1:10 to 1:3, the first portion having dimensions that enable operation with sludge having biological activity measured as oxygen uptake rate in units of milligrams of oxygen per gram of mixed liquor suspended solids per hour of up to 300, and a solids content of up to 15 pounds of biological solids per square foot of vessel floor area; (iii) aerating and mixing the effluent at least in the second portion of the tank; (iv) ceasing the aeration and mixing to allow sludge in the second portion to settle, while still allowing effluent to enter the tank through the inlet; (c) removing the treated effluent in the filtration section by: (i) providing the membrane filtration section with one or more ultrafiltration or microfiltration membrane assemblies submerged in mixed liquor at ambient pressure; (ii) drawing filtrate through the membrane assemblies; and (iii) providing air bubble scouring of the membrane assemblies only during periodic backwash cycles of the filtration system, and not during filtration cycles, wherein the air bubble scouring provided during the backwash cycle has a duration of 1/12 to 1/40 of the filtration time; and (d) repeating the aerating, settling and removing steps to treat additional effluent. 2. The process of claim 1 comprising providing the transverse baffle with at least one aperture. 3. The process of claim 1 comprising providing the tank with a length and width in which the length is about 3.5 to 6 times the width. 4. The process of claim 1, wherein step (e) comprises providing the membrane filtration zone in a baffled compartment within the second portion of the tank. 5. The process of claim 1, wherein step (e) comprises providing the membrane filtration zone in a third portion of the tank separated from the second portion. 6. The process of claim 5, wherein the third portion of the tank comprises a transverse baffle positioned to cause the mixed liquor to have a vertical upward flow past the membrane. 7. The process of claim 1, wherein step (e) comprises decanting the treated effluent from the second portion of the tank into the membrane filtration zone. 8. The process of claim 7, comprising providing the aerating and mixing step for about 2-6 units of time, the decanting step for about 1 unit of time, and the removing step using the membrane assemblies for about 2-5 units of time. 9. The process of claim 1, comprising providing a plurality of biological treatment basins and providing a single membrane filtration zone adapted to receive and process effluent from the plurality of biological treatment basins. 10. The process of claim 1, comprising providing a plurality of membrane assemblies, each separated from adjacent membrane assemblies by a baffle. 11. The process of claim 1 further comprising providing the floor underneath the membrane assembly with a slope from a deeper end adjacent one end of the membrane assembly to a shallower end adjacent an opposite end of the membrane assembly, the slope of the floor angled to direct flow upward toward the membrane assembly. 12. The process of claim 1 further comprising balancing solids in the membrane section by recycling a quantity of liquid from the membrane section back to the inlet of the SMBR, the quantity of liquid comprising a volume in a range of about 10% 20% of a total flow to the SMBR. 13. The process of claim 12, wherein the recycle flow is returned to the inlet only during a backwash cycle of the membranes. 14. The process of claim 1 further comprising periodically providing air to the coarse air bubble diffusers during the filtration cycle at a flowrate insufficient to provide air scouring but sufficient to keep the air header free of sediment. 15. A membrane bioreactor (MBR) comprising: a discrete biological section physically separated from a discrete membrane filtration section, the discrete biological section adapted to receive substantially continuous feed of effluent; one or more fine bubble air diffusers, connected to an air source, for providing dissolved oxygen in the biological section; a sensor for measuring oxygen concentration in the biological treatment section; a controller for controlling air input to the fine bubble air diffusers to maintain a desired measured dissolved oxygen concentration in the biological treatment section; one or more ultrafiltration or microfiltration membrane assemblies submerged in mixed liquor at ambient pressure in the membrane filtration section; one or more feed pumps connected to a discharge manifold for transferring feed from the biological treatment section to the membrane filtration section to be filtered by the membrane, the discharge manifold having an outlet underneath each membrane assembly; one or more filtrate pumps for continuously drawing filtrate through the membrane assemblies, except during periodic backwash cycles; one or more coarse bubble air diffusers, connected to the air source and positioned underneath the membrane assemblies; and a controller set to control air supply to the coarse bubble air diffusers such that air is provided primarily during the backwash cycle and optionally, minimally during a filtration cycle, to provide an air scour time that is in a range of 1/12 to 1/40 of filtration time. 16. The membrane bioreactor of claim 15 further comprising a plurality of membrane assemblies separated from one another by baffles. 17. The membrane bioreactor of claim 16, wherein the floor underneath the membrane assembly has a slope from a deeper end for accommodating the discharge manifold adjacent one end of the membrane assembly to a shallower end adjacent an opposite end of the membrane assembly, the slope of the floor angled to direct flow from the discharge manifold upward toward the membrane assembly. 18. The membrane bioreactor of claim 15 further comprising one or more sensors for measuring mixed liquor suspended solids concentration in the biological treatment and membrane filtration sections, and means for removing sludge from the MBR to maintain a desired mixed liquor suspended solids concentration. 19. A process for treating effluent comprising the steps of: providing the membrane bioreactor (MBR) of claim 15; providing a substantially continuous feed of effluent to the MBR; continuously providing fine bubble aeration in the biological section; continuously drawing filtrate through the membrane assemblies, except during periodic backwash cycles; controlling air input to the fine bubble air diffusers to maintain a desired measured dissolved oxygen concentration in the biological treatment section; and controlling air supply to the coarse bubble air diffusers primarily during the backwash cycle and, optionally, minimally during the filtration cycle, to provide air scour time in the range of 1/12 to 1/40 of filtration time. 20. The process of claim 19, comprising providing a plurality of biological treatment basins and providing a single membrane filtration zone adapted to receive and process effluent from the plurality of biological treatment basins. 21. The process of claim 19 wherein treatment in the biological section comprises providing one or more basins each having a length and width in which the length is 3.5 to 6 times the width, each basin compartmentalized into an anoxic section and an aeration section, the aeration section having an air transfer rate in a range of 0.4 to 0.6 AS and operated at a mixed liquor suspended solids (MLSS) in a range of 2000 to 9000 mg/l. 22. The process of claim 19 further comprising monitoring and controlling the MLSS in the biological section by withdrawing sludge to maintain the MLSS in range. 23. The process of claim 19, comprising providing a plurality of membrane assemblies, each separated from adjacent membrane assemblies by a baffle. 24. The process of claim 19 further comprising providing the floor underneath the membrane assembly with a slope from a deeper end for accommodating a mixed liquor discharge manifold adjacent one end of the membrane assembly to a shallower end adjacent an oppsite end of the membrane assembly, the slope of the floor angled to direct flow from the discharge manifold upward toward the membrane assembly. 25. A membrane filtration system comprising: a sequenced batch reactor comprising a biological section and a membrane filtration section, the biological section comprising a tank divided into a first portion adjacent a tank inlet and a second portion remote from the tank inlet, wherein a volume ratio of the first portion to the second portion is between about 1:10 to about 1:3, the first portion having dimensions that enable operation with sludge having biological activity measured as oxygen uptake rate in units of milligrams of oxygen per gram of mixed liquor suspended solids per hour of up to 300, and a solids content of up to 15 pounds of biological solids per square foot of vessel floor area; the membrane filtration section comprising one or more ultrafiltration or microfiltration membrane assemblies submerged in mixed liquor at ambient pressure; one or more coarse bubble air diffusers, connected to an air source, for scouring each membrane assembly; and a controller programmed to cause a sequence of steps comprising (a) aerating and mixing the effluent at least in the second portion of the tank; (b) settling the sludge in the second portion of the tank by ceasing the aeration and mixing, yet still allowing effluent to enter the tank through the inlet; (c) removing effluent via the membrane filtration section; and (d) repeating the aerating, settling and removing steps, the controller further programmed to supply air to the air diffuser at a flowrate sufficient for scouring the membranes only during a backwash cycle of the filtration system and not during a filtration cycle, such that air scour time is in a range of 1/12 to 1/40 of filtration time. 26. The system of claim 25 further comprising a plurality of membrane assemblies separated from one another by baffles. 27. The system of claim 25 further comprising one or more pumps connected to a discharge manifold for recirculating liquid to be filtered by the membrane, the discharge manifold having an outlet underneath each membrane assembly. 28. The system of claim 27, wherein the floor underneath the membrane assembly has a slope from a deeper end for accommodating the discharge manifold adjacent one end of the membrane assembly to a shallower end adjacent an opposite end of the membrane assembly, the slope of the floor angled to direct flow from the discharge manifold upward toward the membrane assembly. 29. The system of claim 25, wherein the controller is further programmed to periodically supply air to the coarse air bubble diffusers during the filtration cycle at a flowrate insufficient to provide air scouring during the filtration cycle but sufficient to keep the air header free of sediment.