During the clarification process, there is the separation of liquid and solids. The solids are sent to the Gravity Sludge Thickener, another settling tank that further separates solids from liquids. You can see in the video, the arm moves very slowly to move all of the floating solid waste to the bottom of the thickener.
![](https://i.ytimg.com/vi/V7UoPG5QIbQ/maxresdefault.jpg)