Polishing ponds provide which stage of treatment?

• A. Primary treatment
• B. Tertiary treatment
• C. Secondary treatment
• D. No treatment

Answer: (B)

Polishing ponds are used after the main biological treatment to refine the effluent and bring water quality closer to discharge standards. They give additional residence time for the wastewater, allowing remaining fine solids to settle and the residual organics to be further degraded by natural biological processes. This finishing step, often involving natural settling, biological polishing, and sometimes disinfection, is what characterizes tertiary treatment. It’s not the initial settling of solids (primary) or the main biological stage (secondary), and it isn’t “no treatment” because it adds an important finishing step to improve effluent quality.