Question

The chemical method for treatment of water pollution is:

• A. Activated sludge
• B. Sedimentation
• C. Coagulation
• D. Reverse osmosis

Hint:

When classifying water treatment steps, remember: - Physical: Uses gravity or barriers (Sedimentation, Filtration, Reverse Osmosis). - Chemical: Uses chemical reactions (Coagulation, Chlorination, Ozonation). - Biological: Uses living organisms (Activated Sludge, Trickling Filters).

Answer 1

The Correct Option is C

Concept: Environmental engineering classifies wastewater treatment operations into three primary categories based on their underlying mechanisms: physical unit operations, chemical unit processes, and biological unit processes. Chemical methods rely on adding specific reagents to alter the molecular state, pH, surface charge, or solubility of pollutants, making them easier to separate from water. Step-by-step Explanation: Let us systematically analyze the scientific mechanism behind each listed technique:
• Activated Sludge (Option A): This is a biological method. It uses a mixed community of aerobic microorganisms to oxidize and consume dissolved organic matter within an aerated tank, converting pollutants into stable biological flocs.
• Sedimentation (Option B): This is a physical method. It relies on gravitational forces to settle out heavy suspended solids at the bottom of a clarifier tank, without changing the chemical structure of the water.
• Coagulation (Option C): This is a definitive chemical method. Very fine suspended particles and colloidal matter carry negative surface electrical charges that cause them to repel one another, keeping them permanently suspended. Adding chemical coagulants (such as Alum, $\text{Al}_2(\text{SO}_4)_3$, or Ferric Chloride, $\text{FeCl}_3$) neutralizes these surface charges. This chemical reaction allows the destabilized particles to stick together and form larger, heavier masses called flocs that settle out easily.
• Reverse Osmosis (Option D): This is a physical/mechanical separation method. It forces water under high pressure through a semi-permeable membrane to screen out dissolved ions based on molecular size. Therefore, coagulation represents the chemical treatment method.