Hobrafilt
DEPTH FILTER SHEETS
Characteristics
A filtersheet is essentially a three-dimensional, deep filter consisting of adsorbents of a large inner surface. This can be imagined as a labyrinth of little chambers and channels of different lengths inside the sheet where dirt is captured. Contrary to screen filtration, the presence of adsorbents in a deep filtersheet will multiply the total filtration area and, thereby, increase the quantity of the solution being filtered.
Filtration mechanism
Three different filtration types as specified below are applied in the filtration process over filtersheets. In practice, normally, none of the three filtration mechanisms occurs separately during filtration due to the wide range of particle size but they are more or less combined, which is decisive for the filtration result.
- Mechanical filtration – direct filtration of foreign substances. All particles greater than the filtersheet holes are captured mechanically on its surface.
- Electrostatic adsorption – light molecular interactions, Van der Waals forces, occurring among the particles of solutions and the filtersheet material and ensuring that particles smaller than the dimensions of the sheet's inner pores are captured in the little chambers and channels of the filtersheet.
- Electrokinetic adsorption – this is based on the existence of Zeta potential and is applied in microbiologically effective sheets. Excellent filtration/separation effects towards negatively charged particles of dirt, microorganisms and viruses suspended in the liquid being filtered are achieved through the change of the naturally negative electrokinetic charge of the filtersheet to positive - i.e. Zeta potential. This is achieved by a special treatment with polyelectrolytes that are not harmful to health. This treatment makes it possible to capture particles up to ten times smaller than the dimensions of the filtersheet pores.
