Ferric sulfate has which advantage over aluminum sulfate (alum)?

• A. Lower cost
• B. It is less harmful to aquatic life
• C. More dense floc
• D. Better pH control

Answer: (C)

Choosing ferric sulfate has the advantage of producing more dense floc in water treatment processes. This denser floc is beneficial because it settles more quickly and efficiently during the clarification stage, which can improve the overall effectiveness of the sedimentation process. A denser floc can enhance the removal of impurities and suspended particles from the water, leading to clearer and cleaner treated water.

In comparison, while aluminum sulfate (alum) is also used for coagulation, the floc it forms is generally lighter and less dense. This can result in slower settling rates and less efficient removal of contaminants.

The other options, such as lower cost or less impact on aquatic life, may not distinctly favor ferric sulfate over aluminum sulfate, as price can vary based on market conditions and environmental impacts are complex and depend on specific circumstances in which these chemicals are used. Moreover, while ferric sulfate can assist in better pH control in certain situations, aluminum sulfate also has its own mechanisms for pH management depending on the water chemistry involved. Therefore, the production of a more compact floc is a clear and significant advantage of using ferric sulfate in water treatment applications.