One purpose of preliminary treatment is to remove materials that are not readily biodegradable.

• A. Non-biodegradable
• B. Readily Biodegradable
• C. Inert Solids
• D. Nutrients

Answer: (B)

The main idea is that preliminary treatment is aimed at removing solids that won’t break down quickly in the biological stages that follow. These inert solids—things like plastics, grit, and other debris—are not readily biodegradable, so letting them pass would lead to equipment wear, clogging, and inefficiencies in later treatment steps. By removing them early, the system protects pumps and screens and helps the downstream biological processes operate smoothly. Readily biodegradable materials are the ones the biological treatment is designed to consume, so they aren’t the targets of preliminary removal. Nutrients are typically addressed later in the treatment train, not during preliminary screening. Therefore, the concept best captured here is removing materials that are not readily biodegradable, i.e., inert solids.