NOVELTY - Process for treating wastewater comprises: providing wastewater comprising dissolved and suspended solids; promoting aggregation to produce first mixed liquor; separating first mixed liquor into first solids-lean portion and first solids-rich sludge; anaerobically digesting first solids-rich sludge; separating the digested sludge into second solids-lean portion and second solids-rich sludge; precipitating one of phosphorus containing compound or nitrogen containing compound from the second solids-lean portion; and combining a portion of the second solids-rich sludge with the wastewater.    USE - The process and system are useful for treating wastewater, and sludge (claimed).    ADVANTAGE - The process: reduces energy consumption; and reduces the amount of sludge produced during wastewater treatment.    DETAILED DESCRIPTION - Process for treating wastewater comprises: providing wastewater comprising dissolved and suspended solids; promoting aggregation of at least a portion of the dissolved and suspended solids to produce a first mixed liquor; separating the first mixed liquor into a first solids-lean portion and a first solids-rich sludge; anaerobically digesting a first portion of the first solids-rich sludge to produce an anaerobically digested sludge; separating the anaerobically digested sludge into a second solids-lean portion and a second solids-rich sludge; precipitating one of a phosphorus containing compound and a nitrogen containing compound from the second solids-lean portion; and combining a portion of the second solids-rich sludge with the wastewater. INDEPENDENT CLAIMS are also included for:    (1) a wastewater treatment system comprising: a first treatment unit comprising one of a biological sorption tank (712), an aerobic treatment tank (716), an anoxic treatment tank, or an anaerobic digester (722), the first treatment unit having a treatment unit inlet and a mixed liquor outlet; a first separator (714) having a first separator inlet in fluid communication with the mixed liquor outlet, a first solids-lean fluid outlet, and a first sludge outlet; an anaerobic digester having a digester inlet in fluid communication with the first sludge outlet, and a first digester outlet; a second separator having a second separator inlet in fluid communication with the first digester outlet, a second solids-lean fluid outlet, and a second sludge outlet, the second sludge outlet in fluid communication with the treatment unit inlet; and a precipitation vessel in fluid communication with the second solids-lean fluid outlet; and    (2) a method of increasing the capacity of a wastewater treatment system having a biological treatment train with at least one biological reactor comprising an anaerobic reactor, an anoxic reactor, or an aerobic reactor, a solids-rich outlet of the biological treatment train fluidly connected upstream of an inlet of an anaerobic digester, and a recycle line fluidly connecting an outlet of the anaerobic digester to an inlet of the biological treatment train, comprising: adjusting a fraction of a solids-rich sludge produced in the biological treatment train directed to the inlet of the anaerobic digester to a level at which a concentration of methanogenic bacteria present in the solids-rich sludge produced in the biological treatment train is a substantial fraction of a concentration of methanogenic bacteria present in mixed liquor in the anaerobic digester.    DESCRIPTION OF DRAWING(S) - The diagram shows a process flow diagram illustrating treatment system.    Primary clarifier (711)    Biological sorption tank (712)    Separator (714)    Aerobic treatment tank (716)    Anaerobic digester (722)