What is the effective pH range for removing particulate matter with alum as a coagulant?

The effective pH range for removing particulate matter with alum as a coagulant is 5.5 to 8.5. This pH range is critical because aluminum sulfate (alum) functions optimally under these conditions to form flocs that capture and remove suspended particles from water.

At a pH lower than 5.5, the solubility of alum increases, leading to excessive aluminum ions in the water, which can destabilize the coagulation process and reduce the overall effectiveness of particle removal. Similarly, at pH levels above 8.5, the aluminum hydroxide precipitates can form more rapidly and may not effectively interact with the particulate matter, reducing its coagulative properties.

Maintaining the pH within the range of 5.5 to 8.5 ensures that the coagulation reaction proceeds efficiently, allowing for optimal floc formation and subsequent sedimentation or filtration of particulate matter from the water supply. Hence, this pH range is essential for maximizing the effectiveness of alum in water treatment processes.