A process for degrading sludge produced by treatment of wastewater comprising: (a) providing an aerobic treatment system receiving a supply of said wastewater, wherein said aerobic treatment system produces aerobic sludge during operation; wherein said aerobic sludge comprises waste activated sludge and return activated sludge; (b) treating substantially all of said waste activated sludge in a sludge treatment unit in fluid communication with said aerobic treatment system by rupturing microbial cells present in said waste activated sludge to produce treated activated sludge having an increased liquid:solid ratio and an increased degradation potential in comparison to untreated sludge, wherein said treating comprises passing said waste activated sludge through a high pressure nozzle in said sludge treatment unit to substantially lyze microbial cells present in said waste activated sludge; (c) conveying substantially all of said treated activated sludge from said sludge treatment unit to said aerobic treatment system for co-digestion with said wastewater, wherein said treated activated sludge is conveyed to said aerobic treatment system without dewatering or solids removal downstream of said sludge treatment unit, and wherein said aerobic treatment system continuously or semi-continuously receives said supply of said wastewater and a supply of said treated activated sludge; and (d) substantially degrading all of said treated activated sludge in said aerobic treatment system by co-digestion with said wastewater, thereby avoiding the need for a dedicated reactor separate from said aerobic treatment system for degradation of said waste activated sludge, and further avoiding the need for dewatering or disposal of said waste activated sludge; wherein the net mass of particulate solids present in said treated activated sludge degraded in said aerobic treatment system approximates the net mass of particulate solids present in aerobic sludge produced by said aerobic treatment system, thereby substantially avoiding net accumulation of particulate solids in said aerobic treatment system during operation of said process. (a) providing an aerobic treatment system receiving a supply of said wastewater, wherein said aerobic treatment system produces aerobic sludge during operation; wherein said aerobic sludge comprises waste activated sludge and return activated sludge; (b) treating substantially all of said waste activated sludge in a sludge treatment unit in fluid communication with said aerobic treatment system by rupturing microbial cells present in said waste activated sludge to produce treated activated sludge having an increased liquid:solid ratio and an increased degradation potential in comparison to untreated sludge, wherein said treating comprises passing said waste activated sludge through a high pressure nozzle in said sludge treatment unit to substantially lyze microbial cells present in said waste activated sludge; (c) conveying substantially all of said treated activated sludge from said sludge treatment unit to said aerobic treatment system for co-digestion with said wastewater, wherein said treated activated sludge is conveyed to said aerobic treatment system without dewatering or solids removal downstream of said sludge treatment unit, and wherein said aerobic treatment system continuously or semi-continuously receives said supply of said wastewater and a supply of said treated activated sludge; and (d) substantially degrading all of said treated activated sludge in said aerobic treatment system by co-digestion with said wastewater, thereby avoiding the need for a dedicated reactor separate from said aerobic treatment system for degradation of said waste activated sludge, and further avoiding the need for dewatering or disposal of said waste activated sludge;