Which term corresponds to treatment that includes primary, secondary, and tertiary stages?

• A. Drinking water treatment
• B. Photovoltaic (PV)
• C. Wastewater treatment
• D. Hydropower

Answer: (C)

Three-stage treatment describes how wastewater is cleaned: first, solids are physically removed (primary), then organic matter is broken down biologically (secondary), and finally a polishing step removes nutrients and remaining contaminants (tertiary). This sequence is fundamental to wastewater treatment, turning sewage into effluent that can be safely discharged or reused. The other options refer to different concepts: drinking water treatment aims to render water potable and uses methods like coagulation, clarification, filtration, and disinfection, not the same primary/secondary/tertiary framing. Photovoltaic and hydropower are about generating energy from sunlight or water flow, not treating wastewater.