Question

The last step in the wastewater treatment is a ____________ process.

• A. biological
• B. mechanical
• C. chemical
• D. physical

Answer 1

The correct option is C

chemical

Explanation for the correct answer: (C) Chemical:

• Wastewater treatment plant is a facility that treats wastewater from domestic as well as industrial sources.
• The last or the tertiary process involved in the treatment is a chemical process.
• In this process chemicals are added to remove phosphorus and nitrogen from water.
• Chlorine is added to remove harmful micro-organisms and disinfect the water.

Explanation for the incorrect answers:

(A) Biological:

• The secondary process in wastewater treatment is a biological process.
• In this step, organic matter in the sludge are broken down with the help of bacteria.

(B) Mechanical:

• The primary process in wastewater treatment is a biological process.
• First sewage is passed through screens of vertical bars.
• Then the wastewater is passed through grit and sand removal tanks called grit chamber.

(D) Physical:

• A part of the primary process involves the physical process of sedimentation.
• In this process water is put in a sedimentation tank where solid wastes like faeces settle down at the bottom.

Therefore, the correct answer is (C) chemical.