In which treatment process is biological decomposition primarily employed?

• A. Primary treatment
• B. Sludge digestion
• C. Tertiary treatment
• D. Clarification

Answer: (B)

Biological decomposition is primarily employed in the sludge digestion process, which is designed to break down organic materials present in the sludge generated during wastewater treatment. During this process, microorganisms such as bacteria play a crucial role by feeding on the organic matter, effectively reducing its volume and stabilizing it. This not only reduces odors and pathogens but also transforms the organic materials into more manageable forms, such as biogas, which can be captured and used as a source of energy.

While other treatments, such as primary treatment, do involve some biological aspects, they primarily focus on physical processes like sedimentation to remove solids from the wastewater. Tertiary treatment aims to further purify the treated water through advanced filtration and chemical treatment methods but does not primarily hinge on biological decomposition. Clarification serves primarily to settle solids out of the water, which is also a physical separation process, rather than a biological one. Thus, sludge digestion is the correct choice, emphasizing the role of biological processes in wastewater treatment.