Which one of the following is known as the heart of sewage treatment?

Correct option is B

Secondary treatment is considered the heart of sewage treatment because it is the stage where biological processes play a crucial role in removing organic matter from wastewater. This step relies on microorganisms, such as bacteria, to break down organic pollutants in the sewage. It is essential for reducing the biological oxygen demand (BOD) and improving water quality.
Key Features of Secondary Treatment:
1. Purpose: To biologically degrade dissolved and suspended organic matter using aerobic or anaerobic processes.
2. Processes Involved:
· Aerobic Treatment: Includes activated sludge systems, trickling filters, and oxidation ponds.
· Anaerobic Treatment: Includes anaerobic digesters for breaking down organic sludge.
3. Importance: It significantly reduces organic pollution, making the water safe for further treatment or discharge into the environment.
Information Booster:
1. Biological Oxygen Demand (BOD): Reduced significantly in secondary treatment, indicating improved water quality.
2. Microorganisms: Bacteria and protozoa play a major role in degrading organic pollutants.
3. Activated Sludge Process: A widely used method in secondary treatment for its efficiency and effectiveness.
4. Efficiency: Secondary treatment typically removes 85–90% of organic pollutants.
5. End Goal: Produces effluent suitable for tertiary treatment or safe discharge into natural water bodies.
Additional Knowledge:
· Primary Treatment (a): Removes about 50–60% of suspended solids but does not address dissolved organic pollutants.
· Tertiary Treatment (c): Enhances water quality by removing nutrients, pathogens, and fine suspended solids, making it suitable for reuse or safe discharge.
· Advanced Treatment (d): Focuses on removing micropollutants, pharmaceuticals, and heavy metals for specific reuse applications.