Sand or disc filter
In a continuous sand filter, biologically purified waste water is passed through a filter bed consisting of grains of sand, which retain the floating particles. Using an airlift, this sand is continuously circulated over a sand washer, and the particles removed. A more compact alternative to a sand filter can be a disc filter. Here the particles are filtered through filter plates that can be rinsed clean via rotation and a spray system.
The aim of this technique is to remove further suspended matter from the effluent, so as to make it reusable.