One purpose of a WWTP is to satisfy the oxygen demand of the waste flow before it's discharged to the environment?

• A. To oxidize pathogens before discharge
• B. To remove solids in the primary clarifier
• C. To disinfect the effluent
• D. To satisfy the oxygen demand of the waste flow before discharge

Answer: (D)

Wastewater contains biodegradable organic matter that would consume dissolved oxygen if released untreated. A treatment plant lowers that biodegradable organic load, reducing the biochemical oxygen demand so the effluent doesn’t rob the receiving water of oxygen after discharge. That’s the purpose described here: easing the oxygen burden the waste would impose on the environment. Other plant functions like removing solids, disinfection, or oxidizing pathogens are important for different reasons, but they’re not about meeting the oxygen demand of the waste before discharge.