Question

Arrange the following steps involved in the sewage treatment in correct order from initial to the last.
A. Coagulation and Flocculation
B. Chemical disinfection
C. Screening
D. Distribution of treated water
E. Sediment and filtration
Choose the correct answer from the options given below:

• A. E, C, B, A, D
• B. C, E, B, A, D
• C. C, E, A, B, D
• D. C, A, B, E, D

Hint:

Standard wastewater treatment sequence:
1. Screening (preliminary physical removal).
2. Primary sedimentation (gravity settling).
3. Secondary/tertiary coagulation and flocculation.
4. Disinfection (chlorination to kill pathogens).
5. Effluent distribution or reuse.

Answer 1

The Correct Option is C

Concept:
Sewage and wastewater treatment comprises sequential stages: preliminary, primary, secondary, and tertiary treatments.
These stages progressively remove large floating solids, settleable organic sludge, colloidal matter, and pathogenic organisms before the treated effluent is redistributed or discharged.

Step 1: Step-by-Step Wastewater Treatment Process:
1. Screening (C): The initial preliminary physical step. Raw influent passes through coarse and fine bar screens to intercept large floating debris, plastics, and rags to prevent clogging of downstream pumps.
2. Sedimentation and Filtration (E): In primary treatment, wastewater enters primary settling basins where gravity settling separates settleable suspended organic solids as primary sludge, followed by filtration to remove coarse particulate matter.
3. Coagulation and Flocculation (A): Chemical coagulants (such as alum or ferric chloride) are mixed into the water to destabilize colloidal charges, followed by gentle flocculation to form settleable flocs.
4. Chemical Disinfection (B): Disinfectants such as chlorine gas, sodium hypochlorite, or ozone are added to destroy pathogenic bacteria, viruses, and parasites before water release.
5. Distribution of Treated Water (D): The final step where treated, disinfected water is pumped through pipelines for municipal reuse, agricultural irrigation, or safely returned to water networks.

Step 2: Chronological Sequence of Operations:
Arranging these operational stages in order:
C (Screening) arrow E (Sediment and filtration) arrow A (Coagulation and Flocculation) arrow B (Chemical disinfection) arrow D (Distribution)
Final Answer:
The correct operational order is C, E, A, B, D, which corresponds to option (C).