What is the primary purpose of preliminary treatment in a wastewater treatment plant?

• A. Remove larger, inorganic materials, and grit from the wastestream
• B. Remove dissolved organic matter
• C. Add disinfectant
• D. Convert ammonia to nitrate

Answer: (A)

The primary purpose of preliminary treatment is to remove large, inorganic materials and grit from the waste stream before it enters the rest of the treatment process. Screens pick out big solids that could clog pipes or damage pumps, and grit chambers remove heavy inorganic particles like sand and gravel that would cause wear and abrasion downstream. By doing this early removal, downstream equipment runs more smoothly and the overall treatment process operates more efficiently. Dissolved organic matter is addressed later by biological or chemical treatment, not by preliminary screening; disinfectant is added after treatment; and converting ammonia to nitrate (nitrification) occurs in the biological stage, not during preliminary screening.