In a sludge dewatering system, digested sludge with polymer solution added to promote flocculation is delivered to, and fills a treatment tank to a predetermined level The sludge is then agitated to liberate contained gases, and low vacuum of no more than 20 inches of Hg below ambient air pressure is applied to a zone in the tank above the sludge to remove gases and to assist in degassing the sludge. The sludge is then delivered to the centrifuge, preferably a decanter-type, where solids recovery rates can approach 99.5 %.