When needed, what is the goal of tertiary wastewater treatment?

• A. Nutrients and pathogens
• B. Remove settable solids
• C. Increase turbidity
• D. Increase dissolved salts

Answer: (A)

Tertiary wastewater treatment aims to finish polishing the water by removing substances that still pose environmental or health risks after the initial treatment steps. The main goal is to remove nutrients, like nitrogen and phosphorus, which can fuel algal blooms in rivers and lakes, and to reduce pathogens to protect public health. Disinfection and advanced nutrient-removal processes are typical parts of this stage, helping the effluent meet strict quality standards for discharge or reuse.

Removing settable solids is handled earlier in primary and secondary treatment, not the primary focus of tertiary treatment. Increasing turbidity would indicate more suspended material, which is undesirable, and increasing dissolved salts isn’t the objective of tertiary treatment either, since higher salinity can limit usability of the water.