Which treatment is specifically designed to target pollutants that remain after primary and secondary treatments?

Tertiary treatment is specifically designed to address pollutants that persist after primary and secondary treatments in wastewater management. Primary treatment involves the removal of solid materials, while secondary treatment focuses on biological processes to break down organic matter. However, these two stages do not effectively remove all contaminants, particularly nutrients like nitrogen and phosphorus, as well as pathogens and some remaining suspended solids.

Tertiary treatment comes into play after these initial stages to further purify the effluent. This level of treatment can include various processes such as advanced filtration, chemical treatments (like chlorination or ozonation), and biological nutrient removal systems to target and eliminate these remaining pollutants. By achieving higher standards of water quality, tertiary treatment ensures that the water released back into the environment or reused is less harmful.

The other treatments mentioned—preliminary, secondary, and processes like activated sludge—are essential steps in wastewater management but do not focus specifically on the residual pollutants remaining after the earlier treatment phases. Thus, tertiary treatment is integral for achieving comprehensive wastewater treatment objectives.