Patent ID: 7695624
Filing Date: 2010-04-13
Classification: B01D,C02F,Y02W

Abstract:
1. A method of biologically treating wastewater in a membrane bioreactor comprising: a. directing wastewater into a treatment tank and biologically treating the wastewater in the treatment tank; b. directing the biologically treated wastewater as mixed liquor from the treatment tank to a bottom portion of a downstream filtration tank having at least one submerged membrane module that extends across substantially the entire cross sectional area of the filtration tank; c. moving the mixed liquor from the bottom portion of the filtration tank upwardly through the membrane module and constraining the flow of the vertically moving mixed liquor in the filtration tank such that substantially all of the mixed liquor received in the bottom of the filtration tank enters the membrane module in the filtration tank; d. as the mixed liquor flows through the membrane module, inducing at least some of the mixed liquor through the walls of one or more membrane filters that form a part of the membrane module, producing a permeate stream and wherein the mixed liquor passing through the membrane module but not filtered by the membrane filters is referred as a non-permeate stream; e. directing the permeate stream from the one or more membrane filters of the membrane module; f. once the non-permeate stream has passed through the membrane module, recycling at least a portion of the non-permeate stream to the treatment tank wherein the recycled non-permeate stream constitutes at least 50% of the mixed liquor directed from the treatment tank to the filtration tank; and g. substantially prohibiting the recirculation of mixed liquor in the filtration tank such that substantially all of the non-permeate stream makes only a single pass through the membrane module before being recirculated to the treatment tank.