Which approach uses natural wetlands to treat wastewater?

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

Answer: (C)

Natural wetlands treat wastewater by harnessing the ecosystem processes that occur in saturated soils. In a wetland-based system, wastewater flows through a constructed or existing wetland where plants, soils, and microbes work together to remove contaminants. Plant roots oxygenate the rhizosphere and provide surfaces for biofilms; sediments trap solids; soils adsorb nutrients and metals; and microbial activity breaks down organic matter and nutrients such as nitrogen through pathways like nitrification and denitrification. This combination effectively reduces biochemical oxygen demand, suspended solids, and nutrients, often with low energy and maintenance costs and with the added benefit of habitat creation.

This approach is distinct from secondary treatment, which relies on mechanical biological processes in aerated tanks; from tertiary treatment, which provides extra polishing steps after secondary; and from septic tanks, which rely on anaerobic digestion in a tank with a drain field rather than a wetland ecosystem.