GAC contactors can be used when the formation of trihalomethanes or other disinfection by-products cannot be prevented by what?

• A. Increasing the chlorine dose
• B. Adjusting the disinfectants or other treatment processes
• C. Filtration methods
• D. Removing organics before disinfection

Answer: (B)

The formation of trihalomethanes (THMs) and other disinfection by-products is largely influenced by the organic material present in the water. When traditional methods of increasing chlorine doses or adjusting other treatment processes do not effectively control the formation of these by-products, granular activated carbon (GAC) contactors become an essential tool.

Using GAC contactors is particularly beneficial because they adsorb organic compounds that can react with chlorine during disinfection, thereby reducing the overall level of THMs formed. If the mere adjustment of disinfectants or treatment processes does not sufficiently mitigate the risk of by-product formation, GAC contactors provide a physical and chemical means of addressing the issue by targeting the precursors of THMs before disinfection occurs.

This option underscores the importance of controlling organic content in water treatment, as it illustrates that merely modifying chlorine levels may not adequately address the problem of disinfection by-products, thus necessitating the use of GAC as a supplemental treatment method.