Question

After which stage in a water treatment plant is it safe to discharge the treated water into water bodies and why?

Answer 1

Treated water is considered safe for discharge into water bodies after the tertiary treatment stage in a water treatment plant. Tertiary treatment represents the most advanced phase of the treatment process, where the focus is on further refining the quality of water beyond what is achieved in primary and secondary treatments.

Primary treatment involves the removal of large solids and sedimentation of smaller particles, while secondary treatment primarily focuses on the biological degradation of dissolved organic matter using microorganisms. While these stages significantly reduce pollutants, the water at this point may still contain dissolved nutrients like nitrogen and phosphorus, as well as residual pathogens, which can be harmful if released into the environment.

Tertiary treatment addresses these remaining contaminants through advanced methods such as filtration, nutrient removal, and disinfection. Filtration removes the fine suspended particles that secondary treatment may not catch. Nutrient removal is crucial to prevent eutrophication, a process where excess nutrients in water bodies lead to algal blooms that can deplete oxygen levels and harm aquatic life. Disinfection, often done through chlorination or ultraviolet light, ensures that any remaining pathogens are killed, reducing the risk of waterborne diseases.