What reason explains why some suspended material in wastewater is not removed by sedimentation in one hour?

Some suspended material in wastewater may not be removed by sedimentation due to having a specific gravity close to that of water. Sedimentation relies on the principle that denser particles will settle out of the water column under the influence of gravity. When suspended particles have a specific gravity that is very similar to that of water, they do not have enough gravitational force acting on them to overcome the buoyancy provided by the water. As a result, these particles remain suspended and do not settle at the bottom of the tank within the sedimentation timeframe.

Conversely, particles that are either significantly denser than water will settle more rapidly, while those with lower specific gravity may float. The presence of chemicals or high turbulence can affect sedimentation by altering particle behavior and interactions, but it is primarily the specific gravity that determines whether a particle will settle effectively in a sedimentation process.