What effect does aluminum sulfate (alum) have on wastewater pH when used in sufficient amounts?

When aluminum sulfate (alum) is added to wastewater, it primarily acts as a coagulant, helping to remove suspended particles and pollutants from the water. In sufficient amounts, alum dissociates into aluminum ions and sulfate ions upon dissolving in water. The aluminum ions can react with water to produce some degree of acidity, leading to a decrease in pH.

Although the direct effect might seem minimal in certain contexts or concentrations, typically, the use of alum is associated with a lowering of pH, especially in larger dosages where the hydrolysis of aluminum ions becomes more pronounced. Thus, the idea that alum has no effect on pH doesn't align with the chemical behavior observed when it is added to wastewater.

In summary, the correct answer relates to the understanding that alum indeed has an effect on pH, notably lowering it when used adequately, making choice C not a valid conclusion in this scenario.