As the TOC increases, the TOC percentage removal required from a source water supply _______.

• A. Increases as alkalinity decreases
• B. Increases as alkalinity increases
• C. Decreases as pH increases
• D. Decreases as temperature increases

Answer: (A)

Alkalinity acts as a buffer that helps keep the treatment pH in the optimal range for removing natural organic matter. When alkalinity is low, there’s less buffering, so dosing coagulants or oxidants can swing the pH away from that optimum. This reduces the effectiveness of TOC removal, so a larger fraction of the TOC must be removed to meet the same target. With higher alkalinity, the pH remains closer to the ideal range during treatment, allowing more TOC to be removed with the same processes, so the required percentage removal is smaller. Thus, the TOC percentage removal required increases as alkalinity decreases.