Granular activated carbon (GAC) filters are particularly effective for which of the following?

Granular activated carbon (GAC) filters are specifically designed to adsorb organic compounds, which includes various taste and odor-causing substances commonly found in water. The large surface area of the activated carbon allows it to trap these contaminants effectively, improving the overall sensory quality of the water. This makes GAC filters particularly valuable in water treatment processes aimed at enhancing palatability and aesthetic qualities for both potable water and wastewater applications.

In contrast, the other choices do not align with the capabilities of GAC filters. For instance, enhancing water hardness and softening water pertain to processes that involve ion exchange or other chemical treatments rather than adsorption. Likewise, while pH levels can be adjusted through different methods, GAC filters do not serve to increase or decrease the pH directly. Therefore, the primary function of GAC filters in removing taste and odor compounds is what sets the correct response apart and emphasizes their significant role in improving water quality.