If THMs are still a problem after softening, and changing the disinfectant is not an option, what other treatment process can be used and what is its disadvantage?

If THMs are still a problem after softening, and changing the disinfectant is not an option, what other treatment process can be used and what is its disadvantage?

• A. Granular activated carbon, rather expensive
• B. Ozone treatment, high energy cost
• C. UV disinfection, no residual
• D. Parallel filtration, slow

Answer: (A)

To reduce THMs when you can’t change the disinfectant, focus on removing the organic precursors before chlorination. Granular activated carbon provides a surface that adsorbs natural organic matter in the water, which are the compounds that lead to THM formation. By lowering these precursors, the potential for THM formation drops downstream, giving you the desired reduction without altering the disinfection chemistry. The main drawback is cost. Implementing GAC involves capital equipment for contactors, plus ongoing operating expenses for regenerating or replacing the carbon and for backwashing and disposal of spent media. Ozone would also reduce organics, but it involves a different, energy-intensive treatment and changes in chemistry, which isn’t allowed here. UV disinfection eliminates pathogens but leaves no residual in the distribution system and doesn’t remove THM precursors, so it doesn’t address THMs directly. Parallel filtration isn’t targeted at THM precursors and wouldn’t reliably resolve the problem on its own.

To reduce THMs when you can’t change the disinfectant, focus on removing the organic precursors before chlorination. Granular activated carbon provides a surface that adsorbs natural organic matter in the water, which are the compounds that lead to THM formation. By lowering these precursors, the potential for THM formation drops downstream, giving you the desired reduction without altering the disinfection chemistry.

The main drawback is cost. Implementing GAC involves capital equipment for contactors, plus ongoing operating expenses for regenerating or replacing the carbon and for backwashing and disposal of spent media.

Ozone would also reduce organics, but it involves a different, energy-intensive treatment and changes in chemistry, which isn’t allowed here. UV disinfection eliminates pathogens but leaves no residual in the distribution system and doesn’t remove THM precursors, so it doesn’t address THMs directly. Parallel filtration isn’t targeted at THM precursors and wouldn’t reliably resolve the problem on its own.