To address algae growth in sedimentation basins, which combination is applied per liter when drains are used?

• A. 5 g Copper Sulfate and 5 g Lime
• B. 10 g Copper Sulfate and 10 g Soda Ash
• C. 10 g Copper Sulfate and 10 g Lime
• D. 5 g Copper Sulfate and 10 g Soda Ash

Answer: (C)

Algae control in sedimentation basins relies on using copper sulfate to kill the algae while lime raises the water’s pH and helps with coagulation and settling. When drains are used, you want both actions in one step: the algaecide to reduce algae growth and the lime to optimize pH so copper sulfate stays effective and the algae flocs settle more readily with the sludge. Applying ten grams of copper sulfate together with ten grams of lime per liter provides that combined effect—sufficient algicidal action plus the pH and coagulation aid needed for efficient sedimentation. Using soda ash instead of lime changes the pH control and coagulation dynamics, and the other options either under-dose the algaecide or pair it with a different pH adjuster.