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

Concept

Sewage treatment is commonly divided into primary, secondary, and tertiary stages according to the kind of removal process used.

The central biological stage uses microorganisms to break down dissolved and colloidal biodegradable organic matter that physical settling cannot remove.

Application

Secondary treatment is that biological stage. Processes such as activated sludge and trickling filters use microbial action to lower the organic load, so secondary treatment is commonly described as the heart of sewage treatment.

Contrast

• Primary treatment mainly removes coarse and settleable solids by screening, grit removal, and sedimentation.

• Tertiary treatment polishes the secondary effluent through processes such as nutrient removal, filtration, or disinfection.

• Advanced treatment uses specialized processes when removal beyond conventional secondary treatment is required.

Result

Therefore, the answer is Secondary treatment.