Patent ID: 8323499

Claim:
A method of biologically treating wastewater are a membrane bioreactor, comprising: a. directing an influent stream of wastewater into a biological treatment tank and biologically treating the wastewater and forming mixed liquor in the treatment tank; b. transferring the mixed liquor from the treatment tank to a downstream filtration tank; c. submerging one or more membrane modules in mixed liquor contained within the filtration tank; d. positioning the one or more membrane modules in the filtration tank such that the membrane modules occupy substantially the entirety of the cross-sectional area of the filtration tank; e. transferring the mixed liquor from the treatment tank to the filtration tank including pumping mixed liquor from the treatment tank into one or more mixed liquor conduits extending through the filtration tank underneath the one or more membrane modules; f. directing mixed liquor from the one or more mixed liquor conduits through orifices formed in an outer wall of the one or more mixed liquor conduits; g. after passing through the orifices in the mixed liquor conduits, the mixed liquor moves vertically through the filtration tank and through the one or more membrane modules in the filtration tank; h. constraining the flow of vertically moving mixed liquor in the filtration tank such that substantially the entire flow of vertically moving mixed liquor in the filtration tank is constrained to move through the one or more membrane modules; i. as the mixed liquor moves vertically through the one or more membrane modules, passing a first portion of the mixed liquor through individual membrane filters forming a part of the one or more membrane modules to produce a permeate; j. directing the permeate from the individual membrane filters and from the filtration tank; k. recycling a second portion of the mixed liquor from the filtration tank to the treatment tank after the second portion of the mixed liquor has passed through the one or more membrane modules; l. wherein at least 50% of the mixed liquor passing into the filtration tank is recycled to the treatment tank; and m. dispersing air from openings in one or more air conduits extending through the filtration tank underneath the membrane modules such that both the air and mixed liquor move upwardly through the membrane modules.