Generally,large sewage treatment plants adopt primary treatment centered on sedimentation and secondary treatment centered on activated sludge method for wastewater,followed by sludge digestion treatment to concentrate,digest,and  dehydrate the sludge.

Activated sludge treatment:

Generally,cationic polyacrylamide with medium to high charge and medium molecular weight is used.

Digestive sludge treatment:

High charge cations are generally used.