Polyacrylamide(PAM),as a water-soluble polymeric flocculant,possesses abundant amide groups on its molecular chains and excellent capabilities in adsorption bridging and charge neutralization.It plays an important role in the treatment of industrial wastewater,municipal sewage and sludge dewatering.Particularly in the treatment of printing and dyeing wastewater with complex components,high chroma and COD content,targeted modification can significantly improve the treatment efficiency,making PAM a key material for the discharge of printing and dyeing wastewater up to standards.

　　In the traditional chemical flocculation treatment system of printing and dyeing wastewater,virgin polyacrylamide can be used as an organic polymeric coagulant combined with inorganic iron salts and aluminum salts.It realizes rapid sedimentation of dye molecules through charge neutralization and floc bridging.However,unmodified PAM has defects such as relatively high cost,limited removal efficiency for hydrophilic dyes,potential toxicity of residual acrylamide monomers,and poor biodegradability,which tend to cause secondary pollution and restrict its independent application in the advanced treatment of printing and dyeing wastewater.

　　The charge properties,molecular structure and degradation performance of polyacrylamide can be precisely regulated through modification methods including anionization,cationization,graft copolymerization with natural polymers and organic-inorganic recombination,which greatly enhances its adaptability to printing and dyeing wastewater.Cationic modified PAM can effectively neutralize anionic dye colloids in printing and dyeing wastewater,with decolorization efficiency of 83.17%~99.40%for typical dyes such as Congo red and acid orange.The flocs are compact and settle rapidly,and the dosage is significantly lower than that of traditional inorganic flocculants.Graft copolymers of natural polymers(starch,cellulose,chitosan)and acrylamide combine the strong flocculation ability of PAM with the biodegradability of biomass materials.In the treatment of printing and dyeing wastewater,the COD removal rate exceeds 75%and the chroma removal rate exceeds 90%.The floc sedimentation speed is increased by 40%compared with virgin PAM,and the biological toxicity of the treated water is reduced by 65%,which meets the green treatment requirements of printing and dyeing wastewater.

　　In the printing and dyeing sludge treatment section,biodegradable flocculants prepared with PAM as the base material and compounded with cationic starch,activated silicic acid and other additives can further improve sludge dewatering performance.The removal rate of suspended solids is increased by 2.57%,and the sludge moisture content is reduced by 0.34%.Meanwhile,the retention rate of total organic carbon in sludge is improved,supporting subsequent resource utilization such as aerobic