Wastewater Treatment Operator Certification Practice Test

What are colloids?

1. Solids that settle rapidly

2. Dissolved solids

3. Solids found in the grit channel

4. Very small, finely divided solids that remain dispersed in a liquid for a long time

The correct answer is: Very small, finely divided solids that remain dispersed in a liquid for a long time

Colloids are defined as very small, finely divided solids that remain suspended in a liquid for extended periods due to their small size and the effects of Brownian motion. This means that colloidal particles are typically in the size range of 1 nanometer to 1 micrometer, which is too small to be removed by conventional filtration methods and do not settle out rapidly under the influence of gravity. In wastewater treatment, understanding colloids is essential because they can significantly affect various processes, including coagulation, flocculation, and sedimentation. Since colloidal particles are small and stable in a liquid, they require specific treatment techniques to remove them effectively from wastewater. The other options do not accurately describe colloids. Solids that settle rapidly refer to larger particles that can be removed through sedimentation. Dissolved solids are particles that are completely dissolved in the liquid and not suspended. Solids found in the grit channel pertain to larger, heavier materials that settle quickly and are removed from the wastewater early in the treatment process.