Waterguide - Filtration

What is filtration?

Filtration is an essential process in water treatment. It is used to remove contaminants such as particles, suspended matter, bacteria, organic substances and chemicals from the water. This primarily mechanical process, which can also have physical and chemical filtration effects, focusses on the separation or purification of suspensions or solutions.

The substances in the water fall into two categories: solid particles and dissolved substances. Solid particles such as suspended solids and granular particles are almost completely removed by filtration if the particle size and density are high enough. In this process, the water flows through a porous medium (filter media) that retains the relevant particles on the surface or inside.

What is a suspension?

A suspension is a heterogeneous mixture of materials consisting of a liquid and finely distributed, insoluble inorganic and organic solid matter (particles (10-2 – 10-6 m) and colloids (10-6 – 10-9 m). A treatment process is used to clean this water and remove insoluble particles and colloids, so that you are left with a solution.

What is a solution?

A solution is a homogeneous mixture of materials consisting of at least two chemical substances, the solvates and the solvent, which makes up most of the solution. In a water treatment context, especially reverse osmosis, the aim is to separate water (solvent) from the dissolved salts (solvates), depending on downstream process requirements.

What types of filtration are there?

Deep filtration: In deep filtration, the water flows through a porous filter medium which, depending on the filter type, absorbs the undissolved particles or colloids mechanically (sieving of relevant particle sizes) and physically (physisorption) or chemically (chemisorption) “deep” inside the medium, which enables it to be retained.

Surface filtration (membrane technology): In pressure-operated surface filtration, the water flows through a semi-permeable membrane, which – depending on the pore dimension – can retain particles, colloids, diatomic or polyatomic molecules (diatomic molecules are in the range of 10-10 m, large molecules with several atoms in the range of 10-9 m) down to individual ions. Over time, the suspended dirt particles form a coating (fouling) on the surface of the membrane. “In the case of dissolved substances, this coating only starts to form once the solubility threshold has been exceeded (scaling).”

Furthermore, the filters are also divided into fine filters, multi-layer filters and sand filters.

Example: Membrane module for reverse osmosis


Surface/membrane filtration through

How can one conceive of the scales involved?

Size comparison:

Dimensions of a sugar cube: 1,6 • 10-2 x 1,6 • 10-2 x 1,1 • 10-2 m

Add 1010 m

1,6 • 10-2 • 1010 m = 160 000 000 m = 160 000 km

-> Circumference of the Earth approx. 40 000 km

You would have to circle the Earth along the equator four times to reach the 1010 m difference.

Herco filter systems:

  • Fine filters and activated carbon filters
  • Backwashable fine filters
  • Safety fittings
  • Sand filters, iron removal filters, activated carbon filters
  • Multi-media filters
  • Side-stream filters for cooling circuits



You can find out more on filtration in our waterguide and product center:

Custom-made filtration unit

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