Why is ozone treatment often followed by granular activated carbon, which removes assimilated organic carbon caused by the action of the ozone treatment?

• A. To Remove Tastes And Odors
• B. To Remove Color
• C. To Prevent The Regrowth Of Bacteria In The Distribution System
• D. To Prevent Nitrification In The Distribution System

Answer: (C)

When ozone treats a water, it oxidizes natural organic matter and often breaks it down into smaller, more biodegradable compounds. These assimilable organic carbons become easy food for bacteria, which can lead to regrowth in the distribution system if they’re not removed. Granular activated carbon after ozonation effectively adsorbs these small, biodegradable organics and the resulting by‑products, reducing the nutrients available for bacteria. By removing this assimilable carbon, the system is less prone to bacterial regrowth, helping maintain water quality and a stable disinfectant residual. Taste, odor, and color removal can also occur with GAC, but the key reason here is preventing bacterial regrowth. Nitrification isn’t directly addressed by this step.