Separation mechanisms

Sieving or surface filtration
- The particles cannot pass through the pores in the filter medium & are retained in a layer which becomes continuously thicker
- The filtration becomes increasingly fine but the volume flowing through decreases continuously
- Cross – flow filtration belong to this type of filtration

Depth filtration
- Increasingly, separation media are used which consist of very porous materials & which as a result of their very large surface & labyrinthine structure compel the liquid to take a very circuitous part
- The particle are thereby held back by a mechanical sieving effect because of their size
- The gradually block the pores & thereby decrease the flow rate through the filter or
- The particles are fixed by adsorption
- This adsorption occurs because of difference in electrical charges between the filter & the material retained
- Sieving & adsorption effects usually occur together