Massachusetts Wastewater Practice Exam

In wastewater treatment, what is a common effect of low mixing speed on floc?

1. It doesn't aggregate properly

2. It settles too rapidly

3. It floats to the top

4. It becomes too thick

The correct answer is: It doesn't aggregate properly

In wastewater treatment, low mixing speed can significantly impact the behavior of floc, which is a mass of coagulated particles in the water. When mixing speed is insufficient, it prevents the floc from properly aggregating. This is because adequate mixing promotes collision and adhesion between particles, enabling them to come together and form larger, more stable aggregates. Without sufficient agitation, the particles may not encounter each other often enough, leading to incomplete floc formation and resulting in lower overall treatment efficiency. Additionally, if the mixing speed is too low, the dispersion of chemicals like coagulants can be ineffective, further diminishing the floc's ability to bind together. This can ultimately lead to a less efficient removal of contaminants during the treatment process.