An apparatus for treating sludge, comprises a press for dewatering the sludge, a compaction device for receiving and compacting sludge dewatered by the press, a shredder for receiving and shredding sludge compacted by the compaction device, and a tube conveyor for conveying shredded sludge from the shredder. The press is controlled to vary the flow rate of the sludge in response to at least one sensed operational parameter of the press, such as the momentary power for operating the press, pressure in the sludge in the press, sludge concentration in the press, sludge feed flow to the press or separated water flow from the press.