Outline the typical stages of a municipal wastewater treatment plant and the purpose of each stage.

• A. Primary treatment removes settleable solids; secondary treatment uses biological processes to degrade organics; tertiary treatment removes nutrients and disinfects.
• B. Primary disinfection; Secondary removes nutrients; Tertiary solids removal.
• C. Primary aeration; Secondary disinfection; Tertiary filtration.
• D. Primary biological digestion; Secondary chemical precipitation; Tertiary just for odor control.

Answer: (A)

Municipal wastewater treatment is designed in stages that progressively remove contaminants: first physical separation to remove settleable solids, then a biological stage to break down remaining organic matter, and finally an advanced stage to remove nutrients and disinfect before discharge.

Primary treatment uses gravity to settle out solids, producing sludge and a clearer effluent. Secondary treatment employs microorganisms in aerated tanks or biofilms to oxidize and degrade dissolved and suspended organics, greatly reducing biochemical oxygen demand and improving water quality. Tertiary treatment goes further to remove nutrients such as nitrogen and phosphorus and to disinfect the water, with additional options like filtration or chemical treatments depending on the plant.

This sequence captures the typical goals: remove solids, then degrade organics, then address nutrients and pathogens. Other descriptions mix up where disinfection or nutrient removal occur or emphasize odor control as the main purpose, which doesn’t align with the standard progression.