Why does filtration typically follow PAC addition in a water treatment plant?

Filtration typically follows PAC (Powdered Activated Carbon) addition in a water treatment plant primarily because the PAC can lead to the formation of floc and particulates that must be removed from the treated water. PAC is added to adsorb organic compounds and improve water quality by enhancing the removal of impurities. As PAC binds to these impurities, it can aggregate and create a mass of particles, leading to an increase in turbidity.

The filtration process that occurs after PAC addition serves to capture and remove these particulates from the water. If not filtered out, the turbidity caused by the PAC and the adsorbed impurities could compromise the clarity and overall quality of the treated water. Thus, the reason for placing filtration after PAC addition is to ensure that these unwanted turbidity-inducing particles are effectively removed, resulting in cleaner and clearer water ready for further treatment processes, such as disinfection.

The other options, while related to different aspects of water treatment, do not capture the primary reason filtration is necessary after PAC addition. PAC does not inherently neutralize pH levels or significantly reduce chlorine demand; those are separate processes in water treatment. While PAC can assist in some degree of disinfection by adsorbing certain contaminants, the primary focus of filtration following