Which statement best describes the function of preliminary treatment?

• A. It removes pathogens from wastewater
• B. It disinfects the effluent
• C. It removes large solids and grit
• D. It equalizes pH

Answer: (C)

Preliminary treatment is all about protecting the plant and its downstream processes by getting rid of the big stuff right away. By removing large solids and grit early on, pumps, screens, and pipes aren’t clogged or worn down, and the rest of the treatment steps can operate more smoothly. In practice, this stage uses bar screens to catch large debris and grit chambers to settle out sand and gravel, which helps prevent damage and fouling later on. Pathogens aren’t the target here—disinfection and pathogen removal happen later, during biological treatment and final disinfection. Equalizing pH is handled in other portions of the plant with chemical dosing and mixing, not the primary job of preliminary treatment. So the best description is that this stage removes large solids and grit.