Massachusetts Wastewater Practice Exam

What is the role of lime in wastewater treatment?

1. Oxygenation

2. Precipitation of metals

3. pH adjustment

4. Filtration

The correct answer is: pH adjustment

Lime plays a critical role in wastewater treatment primarily through its function in pH adjustment. The addition of lime (calcium hydroxide) raises the pH of wastewater, making it less acidic. This is important because many biological processes used in wastewater treatment are optimal at a neutral or slightly alkaline pH. Additionally, raising the pH can enhance the solubility of certain compounds, facilitating processes such as the precipitation of heavy metals, which can then be removed more effectively. While lime can contribute to the precipitation of metals, its primary and most widely recognized function in wastewater treatment is pH adjustment. By maintaining an appropriate pH level, lime ensures that both biological and chemical treatment processes can operate efficiently, supporting overall wastewater management efforts. In contrast, lime does not play a direct role in oxygenation or filtration, which are related to different aspects of the treatment process.