Which chemical is primarily used as a coagulant in wastewater treatment?

Alum, or aluminum sulfate, is a widely used coagulant in wastewater treatment processes. Coagulation is a crucial step in the treatment of wastewater, as it helps to remove suspended solids from the water by causing them to clump together into larger particles that can then be more easily filtered or settled out.

When alum is added to wastewater, it reacts with the particles in the water and neutralizes their charge. This allows the particles to bind together, forming flocs that can then settle to the bottom of a treatment tank or be removed through filtration. The effectiveness of alum in promoting this coagulation process makes it a preferred choice for many wastewater treatment facilities.

In contrast to alum, calcium hydroxide is primarily used for pH adjustment rather than coagulation, while ferrous chloride can act as a coagulant but is less common compared to alum due to cost and handling considerations. Sodium chloride serves a completely different purpose—primarily as a salt— and does not contribute to the coagulation process in wastewater treatment.