What chemical is used for flocculation and to thicken and dewater biosolids?

The use of polymers in wastewater treatment is primarily for the processes of flocculation, thickening, and dewatering of biosolids. Polymers are large molecules that can interact with fine particles in a liquid suspension, causing them to clump together and form larger aggregates known as flocs. This aggregation is essential in wastewater treatment because it enhances the removal of suspended solids from the liquid waste stream.

When polymers are added to biosolids, they effectively increase the settling rate of the solids in a clarifier and improve the efficiency of dewatering processes such as centrifugation or filtration. By promoting floc formation, polymers lead to a reduction in water content of the biosolids, making them easier to handle and dispose of.

Other chemicals listed have different roles or applications in wastewater treatment. Sodium, for instance, is not typically used in the same context as polymers for flocculation. Calcium chloride is primarily used for controlling phosphorus levels and does not serve the same flocculating purpose. Aluminum sulfate is used as a coagulant in water treatment but has a different mechanism and application compared to synthetic polymers. Therefore, polymers are the most effective and common choice for the specific chemical functions outlined in the question.