What advantage does ferric sulfate have over alum as a coagulant?

Ferric sulfate is advantageous over alum as a coagulant primarily due to its ability to produce a more dense floc. This denser floc enhances the settling process during sedimentation, allowing for more efficient removal of particulate matter and impurities from the water. The denser nature of the floc improves the overall clarity of the treated water because it tends to settle faster and more completely than the floc produced by alum.

In terms of the other considerations, while factors like cost, effectiveness at high temperatures, and color removal are important in the context of coagulation, they do not directly influence the immediate benefit of floc density. Ferric sulfate does exhibit some advantages in these areas, but the key distinguishing feature remains its production of denser, more robust floc, which is crucial for effective water treatment processes.