What is the purpose of tertiary wastewater treatment?

The purpose of tertiary wastewater treatment is to further refine and improve the quality of secondary effluent before it is released into the environment or returned for reuse. This process is essential for removing remaining contaminants, particularly nutrients like nitrogen and phosphorus, which can contribute to water pollution and eutrophication in receiving waters.

Tertiary treatment often involves advanced filtration, chemical treatment, and biological processes designed specifically to target and reduce these nutrients and other pollutants that are not adequately removed during secondary treatment. The term "polishing" suggests that this stage fine-tunes the water quality to ensure it meets strict regulatory standards for discharge or reuse, thereby safeguarding public health and the environment.

In contrast, the other options do not accurately represent the primary aim of tertiary treatment. For instance, prevention of solid removal is not a goal of this stage, nor is it primarily focused on reducing pathogenic organisms or organic contaminants through microbial action, as these are typically addressed in earlier stages of treatment.