A wastewater treatment system for biological treatment of wastewater including organic sewage, the system including a liquid process configuration for removal of at least nitrogen and for concentrating biomass, in a continuous flow process, comprising: a plurality of process zones (38, 40, 50, 52), including a first process zone (38, 50) receiving influent wastewater in continuous flow and mixing the influent wastewater with biomass to produce a mixed liquor in the first process zone (38, 50), and including bacteria in the first process zone effective to produce granular biomass as well as flocculent biomass, the first process zone being anaerobic or anoxic to encourage formation of granular biomass, the plurality of process zones including at least a second process zone (40,52) receiving mixed liquor in continuous flow from the first process zone, including granular biomass and flocculent biomass, one of the plurality of process zones being an aerobic zone, a biomass classifier downstream of the process zones, receiving mixed liquor with granular and flocculent biomass, the classifier having separation means for separating out most of the granular biomass from the mixed liquor, so that the classifier produces a first effluent with predominantly flocculent biomass and a second effluent with predominantly granular biomass, a gravity settling clarifier downstream of the classifier and receiving said first effluent (22, 23) from the classifier, the clarifier having a bottom where settled sludge is collected and can be discharged, a first recycle carrying said second effluent from the classifier back to the first process zone (38, 50), while at least periodically wasting a portion of the second effluent, a second recycle for moving a major portion of settled sludge collected in the clarifier bottom to one of the process zones (38, 40, 50, 52),, while a waste outlet of the clarifier at least periodically wastes another portion of the settled sludge from the bottom of the clarifier, flow balancing means (32, 19) for adjusting flow into the classifier to allow for variations in influent flow rate into the system when influent flow is below a desired range, either by recycling a selected portion of said first effluent from downstream of the classifier to upstream of the classifier or by increasing flow at said second recycle (18, 19), and a bypass line for moving a selected portion of biomass from the process zones in a bypass around the classifier, in an amount to allow for variations in influent flow rate to the system above the desired range. a plurality of process zones (38, 40, 50, 52), including a first process zone (38, 50) receiving influent wastewater in continuous flow and mixing the influent wastewater with biomass to produce a mixed liquor in the first process zone (38, 50), and including bacteria in the first process zone effective to produce granular biomass as well as flocculent biomass, the first process zone being anaerobic or anoxic to encourage formation of granular biomass, the plurality of process zones including at least a second process zone (40,52) receiving mixed liquor in continuous flow from the first process zone, including granular biomass and flocculent biomass, one of the plurality of process zones being an aerobic zone, a biomass classifier downstream of the process zones, receiving mixed liquor with granular and flocculent biomass, the classifier having separation means for separating out most of the granular biomass from the mixed liquor, so that the classifier produces a first effluent with predominantly flocculent biomass and a second effluent with predominantly granular biomass, a gravity settling clarifier downstream of the classifier and receiving said first effluent (22, 23) from the classifier, the clarifier having a bottom where settled sludge is collected and can be discharged, a first recycle carrying said second effluent from the classifier back to the first process zone (38, 50), while at least periodically wasting a portion of the second effluent, a second recycle for moving a major portion of settled sludge collected in the clarifier bottom to one of the process zones (38, 40, 50, 52),, while a waste outlet of the clarifier at least periodically wastes another portion of the settled sludge from the bottom of the clarifier, flow balancing means (32, 19) for adjusting flow into the classifier to allow for variations in influent flow rate into the system when influent flow is below a desired range, either by recycling a selected portion of said first effluent from downstream of the classifier to upstream of the classifier or by increasing flow at said second recycle (18, 19), and a bypass line for moving a selected portion of biomass from the process zones in a bypass around the classifier, in an amount to allow for variations in influent flow rate to the system above the desired range.