Energy-efficient biological treatment system with filtration membrane

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, a solids content of up to 15 pounds of biological solids per square foot of vessel floor area, and an F/M ratio in a range of 0.05 to 5;
• the membrane filtration section comprising one or more ultrafiltration or microfiltration membrane assemblies submerged in mixed liquor at ambient pressure, each membrane assembly positioned 100-240 mm from a nearest wall, baffle, or adjacent membrane assembly, and positioned no more than 1 meter above a floor and at least 150 mm below a liquid level line in the membrane filtration section;
• 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 for scouring the membranes only during a backwash cycle of the filtration system and not during a filtration cycle.