Which of the following is not a physical treatment?

• A. Filtration
• B. Sedimentation
• C. Oxidation
• D. Screening

Answer: (C)

The question tests the difference between physical separation methods and chemical reactions used in wastewater treatment. Physical treatments remove contaminants without changing their chemical makeup: screening grabs out large debris, sedimentation allows suspended solids to settle by gravity, and filtration traps particles as water passes through a porous medium. Oxidation, in contrast, is a chemical process that changes the pollutants’ chemical structure by reactions that add oxygen or alter electron states. Because it chemically transforms contaminants rather than merely removing particles, it’s classified as a chemical treatment rather than a physical one. For example, oxidants like chlorine or ozone react with organic and inorganic compounds to break them down, which is a chemical change rather than simple physical separation. Therefore, oxidation is not a physical treatment, while screening, sedimentation, and filtration are.