How do primary and secondary municipal wastewater treatments differ?

How do primary and secondary municipal wastewater treatments differ?

• A. Primary uses biological processes; secondary uses physical separation.
• B. Primary uses chemical coagulation; secondary uses filtration.
• C. Primary uses physical separation (grit removal, sedimentation); secondary uses biological processes (aeration, activated sludge) to degrade organics.
• D. Primary and secondary are identical.

Answer: (C)