Which of the following are the three major stages of sewage treatment?

The three major stages of sewage treatment are Primary, Secondary, and Tertiary.

Primary treatment focuses on the physical processes that remove large solids and sediments from wastewater through sedimentation and screening. This stage aims to reduce the load on subsequent treatment processes and is critical for preventing fouling and damage to equipment.

Secondary treatment enhances the process by using biological methods to further break down organic matter. This stage typically involves aeration tanks, where microorganisms consume the organic pollutants, effectively reducing the biochemical oxygen demand (BOD) in the water.

Tertiary treatment is the final stage and aims to polish the effluent by removing remaining impurities and pathogens. This can involve advanced filtration, chemical disinfection, or nutrient removal processes. Tertiary treatment ensures the water is safe for discharge into the environment or for potential reuse.

Together, these three stages form a comprehensive approach to sewage treatment, addressing solid waste, organic contaminants, and harmful pathogens efficiently and effectively. The other options presented do not encapsulate the full scope of sewage treatment processes as specifically as the Primary, Secondary, and Tertiary framework does.