Which option corresponds to a rural on-site waste treatment tank that collects and decomposes waste?

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

Answer: (D)

A septic tank provides on-site wastewater treatment by collecting household waste and beginning its decomposition through anaerobic digestion. It settles solids to form sludge at the bottom and scum at the top, while the clarified liquid (effluent) exits to a drain field for further treatment in the soil. This setup is characteristic of rural, on-site systems that handle waste locally rather than at a centralized plant.

Wetland-based treatment systems use plants and microbial processes in constructed wetlands to treat wastewater, not a single tank. Secondary and tertiary sewage treatment refer to deeper treatment stages in centralized facilities after initial (primary) treatment, so they aren’t on-site, single-tank solutions.