Which process refers to the stage designed to remove contaminants to very high quality, including nutrients and pathogens?

Which process refers to the stage designed to remove contaminants to very high quality, including nutrients and pathogens?

• A. Secondary Sewage Treatment
• B. Wetland-Based Treatment Systems
• C. Septic Tanks
• D. Tertiary Sewage Treatment

Answer: (D)

The main idea is the polishing step of wastewater treatment that pushes water quality up to a level suitable for reuse or safe discharge. This stage, tertiary sewage treatment, is specifically designed to remove contaminants to very high quality, including nutrients like nitrogen and phosphorus and pathogens. Secondary treatment mainly relies on biological processes to reduce organic matter and some suspended solids, but it doesn’t consistently remove nutrients to low enough levels or kill remaining pathogens. Septic tanks provide only primary treatment by letting solids settle, with limited removal of nutrients or microbes. Wetland-based systems can further reduce pollutants, but they’re not universally the controlled, high-grade polishing step used to meet strict nutrient and pathogen targets. So the best answer is the tertiary stage because it adds advanced processes—such as nutrient removal, disinfection, and sometimes membrane filtration—to achieve very high-quality effluent suitable for reuse or sensitive environments.

The main idea is the polishing step of wastewater treatment that pushes water quality up to a level suitable for reuse or safe discharge. This stage, tertiary sewage treatment, is specifically designed to remove contaminants to very high quality, including nutrients like nitrogen and phosphorus and pathogens. Secondary treatment mainly relies on biological processes to reduce organic matter and some suspended solids, but it doesn’t consistently remove nutrients to low enough levels or kill remaining pathogens. Septic tanks provide only primary treatment by letting solids settle, with limited removal of nutrients or microbes. Wetland-based systems can further reduce pollutants, but they’re not universally the controlled, high-grade polishing step used to meet strict nutrient and pathogen targets. So the best answer is the tertiary stage because it adds advanced processes—such as nutrient removal, disinfection, and sometimes membrane filtration—to achieve very high-quality effluent suitable for reuse or sensitive environments.