Process and energy-efficient biological treatment system with filtration membrane

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.

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.