Question

Microbes have been used by humans in household, industrial and agricultural setups. One such use is shown in the diagram given below.

1. Tank A represents primary treatment of sewage while Tank B shows its secondary treatment. State one difference between the two kinds of sewage treatment. 
2. Identify the tank in which flocs are added. 
3. What is the purpose of using microbes in sewage treatment?

Answer 1

1. • Primary Treatment (Tank A – First Sedimentation): In this stage, physical methods are used to remove large solid particles and some organic matter. In Tank A, sewage is allowed to settle. Heavy particles (sludge) settle at the bottom, while lighter materials like grease float on the surface. About 30–40% of organic matter is removed in this step.
   • Secondary Treatment (Tank B – Aeration): This stage uses microorganisms to break down organic matter present in sewage.
     In Tank B, air is pumped in to help aerobic microbes grow. These microbes digest the organic waste and reduce it by about 85–90%.
2. Flocs: Flocs are groups of bacteria and fungal filaments formed during secondary treatment in the activated sludge process.
   They consume organic matter in the sewage. These flocs are formed in the aeration tank (Tank B) and help in breaking down waste.
3. 
   
   • Pollution Reduction: Microorganisms reduce organic pollutants (measured as BOD), which makes the water cleaner.
   • Safe Disposal: The treated water becomes safe to release into rivers or to reuse.
   • Sludge Management: Microbes help form activated sludge. This sludge can either be reused (sent back to Tank B) or broken down in a digester to produce biogas.