NOVELTY - A method of conditioning mixed liquor in a membrane biological reactor (MBR) involves adding water-soluble cationic, amphoteric and/or zwitterionic polymers for coagulation and flocculation to the mixed liquor.    USE - For conditioning mixed liquor in membrane biological reactors resulting in reduced fouling and increased water flux through the membrane (all claimed).    ADVANTAGE - The water-soluble cationic, amphoteric and zwitterionic polymers in the MBR coagulate and flocculate the biomass in the mixed liquor and precipitate the soluble biopolymer, thereby reducing fouling of the membrane and result in an increase of 500% in membrane flux while leaving virtually no excess polymer in the treated waste water at the effective dose. The method increases membrane flux and permits the use of smaller systems, with a concomitant reduction in capital costs, or alternatively, increases treated wastewater volumetric flow from an existing system, with a corresponding reduction in cost of operation.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (1) a method of clarifying wastewater in a membrane biological reactor (MBR), where microorganisms consume organic material in the wastewater to form a mixed liquor comprising water, the microorganism and dissolved and suspended solids, which involves adding cationic, amphoteric and/or zwitterionic polymers, to form a mixture comprising water, microorganisms and coagulated and flocculated solids and separating clarified water from the microorganisms and the coagulated and flocculated solids by filtration through a membrane;    (2) a method of preventing fouling of a filtration membrane in a MBR, where microorganism consume organic material in the wastewater in a mixed liquor comprising water, the microorganisms and dissolved, colloidal and suspended solids and clarified water in separated from the mixed liquor by filtration through the filtration membrane which involves adding cationic, amphoteric and/or zwitterionic polymers, sufficient to prevent fouling of the membrane;    (3) a method of enhancing flux through a filtration membrane in a MBR; and    (4) a method of reducing sludge formation in a membrane reactor.    DESCRIPTION OF DRAWING(S) - The figure shows schematic diagram of membrane bioreactive system for biological treatment of wastewater.