Which of the following is a sign that sludge needs to be wasted from a clarifier?

The thickening of the sludge layer is a clear indication that sludge needs to be wasted from a clarifier. When sludge accumulates excessively, it can lead to various operational issues within the treatment process. An overly thick sludge layer may hinder proper settling and separation of solids from the liquid phase, potentially resulting in poorer effluent quality. This thickening signifies that the system is not maintaining the appropriate balance of solids and liquid, which is essential for optimal clarifier performance.

Proper management of sludge removal is critical for ensuring that the clarifier operates effectively. Regularly wasting sludge helps maintain a healthy environment for biological processes and prevents the buildup of solids, which can lead to decreased treatment efficiency and potential operational problems downstream. Thus, monitoring the thickness of the sludge layer is an important practice in wastewater management to promote effective treatment processes.