What effect will the addition of alum have on the pH of wastewater?

Adding alum, or aluminum sulfate, to wastewater results in a decrease in pH. This occurs because alum is an acidic compound that, when dissolved in water, undergoes hydrolysis. The hydrolysis process releases hydrogen ions (H+), which leads to an increase in acidity and subsequently lowers the pH of the solution.

The primary function of alum in wastewater treatment is to act as a coagulant, aiding in the aggregation of suspended particles to facilitate their removal. While it is effective in this role, it also impacts the overall chemistry of the water, causing a lowering of the pH. Therefore, when alum is introduced into wastewater, it will generally lead to a more acidic environment, confirming that the addition indeed decreases the pH of the wastewater.