What are the three main stages of wastewater treatment?

The three main stages of wastewater treatment are correctly identified as primary, secondary, and tertiary treatment. Each stage serves a distinct purpose in the overall process of treating wastewater to ensure that it is safe for discharge into the environment or for reuse.

In the primary treatment stage, the main goal is to physically remove large solids and contaminants from the wastewater through processes such as screening and sedimentation. This helps in reducing the load of pollutants before further treatment stages.

The secondary treatment stage focuses on the biological processes that break down organic matter in the wastewater. This is typically accomplished using microorganisms that digest the organic pollutants, significantly reducing the biochemical oxygen demand (BOD) and improving water quality.

Tertiary treatment, or advanced treatment, is the final step, where any remaining impurities are removed. This can include filtration, disinfection (using methods such as chlorination or UV treatment), and nutrient removal to ensure that the effluent meets regulatory standards and is safe for discharge or reuse.

The other options present different terminologies or processes that are not standard stages in conventional wastewater treatment, leading to a misunderstanding of the correct framework used in the field.