What is a sludge blanket in a clarifier?

• A. A layer of clarified liquid that collects at the top
• B. A layer of settled solids that aids in trapping particulates
• C. A layer of floating debris that prevents overflow
• D. A layer of aerated sludge for microbial growth

Answer: (B)

A sludge blanket in a clarifier refers to a layer of settled solids that accumulates just above the bottom of the clarifier. This layer plays a critical role in the treatment process as it helps to trap particulates from the incoming wastewater. The settled solids within the sludge blanket can effectively capture and retain suspended particles, helping to improve the overall clarity of the treated water as it flows upward through the clarifier. This mechanism aids in the removal of contaminants, ensuring that the water leaving the clarifier meets desired quality standards.

In this context, it's important to recognize the other choices. The layer of clarified liquid that collects at the top is the supernatant, not the sludge blanket, which is specifically composed of settled solids. A layer of floating debris would indicate issues with separation rather than effective treatment, and while aerated sludge supports microbial growth, it typically exists in biological treatment processes like aerobic digestion rather than describing a sludge blanket in a clarifier.