What happens to PAC particles when they are coated with coagulants or other water treatment chemicals?

• A. They enhance their capacity to adsorb
• B. They lose their capacity to adsorb
• C. They increase their size
• D. They become ineffective for taste and odor control

Answer: (B)

When PAC (Powdered Activated Carbon) particles are coated with coagulants or other water treatment chemicals, they lose their capacity to adsorb. This happens because the coating can occupy the active sites on the PAC, which are essential for adsorption processes. These active sites are where contaminants, odors, and tastes would normally bind to the PAC. When coagulants or other chemicals adhere to these surfaces, they effectively block contaminants from being adsorbed, thus diminishing the overall effectiveness of the PAC in removing impurities from water.

The interaction between the PAC and coagulants may also change the physical and chemical characteristics of the PAC particles, potentially reducing their overall efficiency in treatment processes. As a result, while coagulants serve important functions in water treatment, such as aggregating suspended solids for easier removal, their presence can impede the ability of PAC to adsorb pollutants, which is vital for maintaining water quality.