SLUDGE DEHYDRATING METHOD

PROBLEM TO BE SOLVED: To provide a sludge dehydrating method which enables dehydrating stably and efficiently organic sludge which contains biologically treated sludge generated from sewage, night soil and industrial waste water, etc. SOLUTION: This sludge dehydrating method is featured in that an amphoteric polymer which has structural units shown by general formula (1), general formula (2) and general formula (3), in which the number of structural units shown by general formula (1) is less than the number of structural units shown by general formula (3), intrinsic viscosity measured at 30 deg.C by making sodium nitrate aqueous solution of 1 mol/L as solvent which is prepared to pH 3 by using of hydrochloric acid aqueous solution of 0.1 mol/L is 5 dL/g or more, the value of gradient k' in ηsp/c=[η]+k'c is 30-50 dL2/g2, the length drawing yarn of 0.4 wt.% aqueous solution at 30 deg.C is 55-75 mm and the extrapolated viscosity at 1 rpm in 0.2 wt.% aqueous solution at 30 deg.C is 1,500-3,500 mPa.s, is added to an organic sludge and the dehydration is performed.