Which process removes organic pollutants in wastewater treatment?

• A. Biological treatment (activated sludge) metabolizes organics by microbes
• B. Filtration only
• C. Ultraviolet treatment only
• D. Sedimentation only

Answer: (A)

Microorganisms break down organic pollutants during biological treatment, turning them into biomass, carbon dioxide, and water. In the activated sludge process, microbes metabolize a wide range of dissolved and colloidal organics, using them as food and energy. Aeration keeps the microbes active, so they continuously digest the contaminants, lowering the organic load (BOD/COD) before the water moves on to secondary clarification where the microbial biomass settles out.

Filtration targets mainly suspended solids and may remove some attached organics, but it doesn’t fundamentally break down dissolved organics. Ultraviolet treatment inactivates pathogens, not the organic molecules themselves. Sedimentation mostly removes solids by gravity, not dissolved organics that have already been dissolved. So the biological treatment step is the primary method for removing organic pollutants from wastewater.