Which statement best describes preliminary treatment?

• A. It adds disinfectant to water.
• B. It reduces the oxygen demand of the flow.
• C. It primarily removes large solids and grit from the wastestream.
• D. It eliminates all pathogens.

Answer: (C)

The main idea behind preliminary treatment is to remove large solids and grit from the incoming wastewater to protect downstream equipment and processes. This step uses things like bar screens and grit chambers to capture bulky debris and abrasive materials (sand, gravel, grit, rags, plastics) so pumps, channels, and subsequent treatment stages can operate smoothly. It’s not about disinfecting water, reducing the oxygen-demanding load, or eliminating all pathogens—those functions occur in later stages of treatment.