Briefly describe the primary steps of a wastewater treatment process.

• A. Physical removal of solids (screening/settling), biological degradation of organics (activated sludge or biofilm), and disinfection with chlorine or alternative methods; possible nutrient removal.
• B. Only chemical precipitation and filtration.
• C. Aeration without solids removal.
• D. Discharging raw wastewater.

Answer: (A)

Wastewater treatment is a sequence of core actions that first separate solids, then biologically degrade the remaining organics, and finally inactivate pathogens before the water is discharged. The physical removal stage uses screening to catch large debris and settling tanks to remove settleable solids, which reduces the load and protects downstream equipment. The biological stage employs systems like activated sludge or biofilm reactors where microorganisms consume organic matter, converting it into microbial biomass, CO2, and treated water, which lowers the organic load (BOD/COD) and helps stabilize the effluent. The final disinfection step uses chlorine, UV, or other methods to kill residual pathogens, ensuring the treated water is microbiologically safe for release; many plants also implement nutrient removal to cut nitrogen and phosphorus levels and protect the receiving water from eutrophication. The other options omit essential parts—relying only on chemical precipitation/filtration ignores the biological degradation and disinfection needs; aeration without solids removal leaves solids and does not achieve proper treatment; discharging raw wastewater bypasses the treatment process entirely.