Wastewater treatment method and membrane bioreactor having mixed liquor and air conduits in a filtration tank

Biologically treated wastewater is directed as mixed liquor from a treatment tank to a downstream filtration tank having a having a submerged membrane module extending across the cross-sectional area of the filtration tank. Mixed liquor is directed from the bottom of the filtration tank upwardly into the membrane module such that substantially all of the mixed liquor received in the bottom of the filtration tank flows through the membrane module. A permeate stream is produced. A portion of a non-permeate stream is recirculated to the treatment tank. The filtration tank is sized such that there is no substantial recycle of mixed liquor in the filtration tank. Once the mixed liquor in the filtration tank makes one pass through the membrane module the mixed liquor is recycled to the treatment tank and generally not permitted to be recycled through the membrane module without first returning to the treatment tank.