What does preliminary treatment remove?

• A. Dissolved organic matter
• B. Large untreatable and inorganic objects
• C. Chlorine residuals
• D. Microorganisms

Answer: (B)

Preliminary treatment is all about removing the big, nonbiodegradable solids and inorganic materials that could damage equipment or clog the system downstream. At the plant headworks, screens capture large debris, and grit removal takes out heavy inorganic particles like sand and gravel. By pulling these out early, the flow is easier to handle for the rest of the treatment steps.

Dissolved organic matter stays dissolved and requires later biological or chemical treatment; chlorine residuals come from disinfection after primary/secondary stages; microorganisms are addressed mainly by the biological treatment that follows. So the option that describes what preliminary treatment removes best is the large untreatable and inorganic objects.