Massachusetts Wastewater Practice Exam 2025 - Free Wastewater Practice Questions and Study Guide

To neutralize a waste stream with a pH of 10.6, the objective is to lower the pH towards a more neutral level, which is typically around 7. The appropriate approach involves adding a substance that is acidic, as this will counteract the alkaline properties of the waste stream.

Sulfuric acid is a strong acid that dissociates completely in water, releasing hydrogen ions (H+) which effectively decrease the pH of the solution. When sulfuric acid is added to a basic solution, the hydrogen ions will react with the hydroxide ions (OH-) present, leading to the formation of water and thereby reducing the overall pH of the waste stream.

In contrast, calcium carbonate, while it can lower pH as it reacts with acids, is more suited to raise pH when reacting with acids due to its buffering capabilities. Sodium hydroxide would further increase the pH, as it is a strong base. A pH 7 buffer would not actively neutralize the alkaline conditions because it is designed to maintain a stable pH rather than change it.

Therefore, the most suitable and effective choice for neutralizing a waste stream with a pH of 10.6 is sulfuric acid, as it