Which of the following is explicitly prohibited from discharge into the collection system due to potential interference with the treatment process?

• A. Volatile organics
• B. High strength BOD/TSS loadings
• C. pH between 5 and 10
• D. Other toxic materials that may interfere with the treatment process

Answer: (D)

The main idea is to keep anything that could harm or disrupt the treatment process out of the sewer. Treatment plants rely on biological and physical processes that can be severely affected by toxic or inhibitory substances. When toxic materials enter the collection system, they can kill or inhibit microbes, upset digestion, cause foaming, corrosion, or other problems that reduce treatment efficiency and damage equipment. Because of that risk, substances described as “other toxic materials that may interfere with the treatment process” are explicitly prohibited from discharging to the sewer.

Volatile organics, high strength BOD/TSS, and pH in a wide range can cause issues and are typically managed by permit limits, pretreatment requirements, or process controls. But the broad category of toxic materials that may interfere with treatment directly targets the kind of substances most likely to jeopardize the plant’s operation, making it the best answer.