Florida Wastewater Practice Test

What is the most likely cause of a high sludge blanket in a clarifier?

1. Too much chlorine addition

2. Filamentous bacteria causing slow settling

3. Low MLSS concentration

4. Rapid influent flow

The correct answer is: Filamentous bacteria causing slow settling

The most likely cause of a high sludge blanket in a clarifier is related to filamentous bacteria causing slow settling. When filamentous bacteria are present in excess, they can create a network of filaments that entraps floc particles, leading to poor settling characteristics. This results in the excess accumulation of solids in the clarifier, contributing to a high sludge blanket. The presence of this type of bacteria indicates that the solids are not settling properly, which can hinder the separation process designed to clarify the wastewater effectively. In contrast, excessive chlorine addition can disrupt the microbial community, and low mixed liquor suspended solids (MLSS) concentration would generally lead to less sludge accumulation in the clarifier. Rapid influent flow can also result in poor settling, but it would typically not lead to a high sludge blanket by itself without the additional influence of settling characteristics affected by bacteria or other factors. Overall, the interaction between filamentous bacteria and the settling process is critical in understanding the formation of a high sludge blanket in clarifiers.