Sludge dehydrating agent and sludge dehydrating method

A sludge dehydrating agent, comprising at least one crosslinked polymer selected from the group consisting of a polymer A, a polymer B, and a polymer C described below, wherein the crosslinked polymer has an intrinsic viscosity of 0.5 to 5.0 dL/g at 30° C. in a 1.0 N aqueous solution of sodium nitrate:

• polymer A:
• a crosslinked polymer wherein a monomer composition of polymer constitutional units comprises 1 to 100 mol % of a cationic monomer represented by the following general formula (1) and 0 to 99 mol % of a nonionic monomer:
• wherein R1 represents a hydrogen atom or a methyl group;
• R2 and R3 each independently represent an alkyl group or an alkoxy group having 1 to 3 carbon atoms, or a benzyl group;
• R4 represents a hydrogen atom, an alkyl group or an alkoxy group having 1 to 3 carbon atoms, or a benzyl group;
• A represents an oxygen atom or a NH group;
• B represents an alkylene group or an alkoxylene group having 2 to 4 carbon atoms;
• and X− represents an anion;
• polymer B:
• a crosslinked polymer wherein a monomer composition of polymer constitutional units comprises 1 to 100 mol % of a cationic monomer represented by the following general formula (2) and 0 to 99 mol % of a nonionic monomer:
• wherein R5 and R6 each independently represent a hydrogen atom or a methyl group;
• and X− represents an anion;
• and
• polymer C:
• a crosslinked polymer wherein a monomer composition of polymer constitutional units comprises 1 to 99 mol % of a cationic monomer represented by the general formula (1), 1 to 99 mol % of an anionic monomer represented by the following general formula (3), and 0 to 98 mol % of a nonionic monomer:
• wherein R7 represents a hydrogen atom or CH2COOY;
• R8 represents a hydrogen atom, a methyl group, or COOY;
• Q represents SO3−, C6H4SO3−, CONHC(CH3)2CH2SO3−, or COO−;
• and Y represents a hydrogen atom or a cation.