Patent ID: 7438805

Claim:
An apparatus for reducing the volume of sludge comprising: a biological oxidizing tank for degrading a sludge extracted from a sewage water treatment device by aerobic treatment; a solubilizing device for solubilizing a sludge generated in the course of biological treatment of extracted sludge in said biological oxidizing tank, to a state readily degradable by microorganisms; means for adjusting the pH of the sludge taken out from said biological oxidizing tank, to 8 to 14, means for injecting the pH-adjusted sludge into said solubilizing device; means for heating the sludge in said solubilizing device to 110° C. to 250° C. at a pressure equal to or higher than saturated steam pressure; means for returning the solubilized sludge taken out in solubilized state from said solubilizing device, to said biological oxidizing tank; and means for adjusting the pH of the sludge in said biological oxidizing tank to 5 to 9.