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Membrane technology

Get particles out of the process water


In membrane technology, process or waste water flows under pressure over specially developed technical membranes made of ceramic or plastic, which function similarly to filters. The separation of ingredients and liquid takes place on the membrane.

In particular, the process can filter suspended solids from the water. The structure of the membrane is selected precisely to suit the application.

How membrane filtration works


Membrane processes, in addition to processes such as distillation or absorption, are separation processes that can be used to separate particulate substances and long-chain organic molecules from water. Depending on the physical and chemical properties of the membrane, water can pass through the membrane and other substances are retained.

The process water is repeatedly pumped from the process water tank into the membrane module by a circulation pump and flows over the surface of the ultrafiltration membrane. The ceramic tubular membrane, specially selected for the particular filtration task, allows the water to pass through but retains macromolecules and particles. The process water passes through the membrane under pressure perpendicular to the direction of overflow and flows purified into the filtrate tank.

With regard to the pore size, different degrees of filtration are distinguished

  • Microfiltration: > 0.1 µm
  • Ultrafiltration: < 0.1 µm
  • Nanofiltration: < 2 nm
  • Reverse osmosis

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Membrane filtration – the processes


Microfiltration

Here, as in ultrafiltration and nanofiltration, filtration works according to the cross-flow principle: the water to be filtered is forced through the filter with overpressure. Depending on the application, the filter can be made of stainless steel, plastic or textile fabric.

To prevent the filter from clogging, a circuit must be set up on the inflow side, through which more water continuously reaches the filter than should pass through it. It is also important to swirl the water on the inflow side so that no cake forms that clogs the filter.

Ultrafiltration

Ultrafiltration reaches a degree of fineness above which even bacteria and viruses can be removed from the water. Unlike a disinfection process, the organic component of this size is completely removed from the water. This makes cold sterilization possible, which is sometimes required in the pharmaceutical industry, for example.

Because of the significantly higher water pressure, ceramic filters are used here which can withstand the high loads permanently.

The process is used in drinking water and wastewater treatment, in the purification of washing or process water, e.g. for the removal of surfactants, and in the food industry for the separation of proteins.

Nanofiltration

Nanofiltration captures even the smallest molecules and multivalent ions. Depending on the dimensioning of the membrane, precisely defined molecules can thus be filtered out. Nanofiltration is usually used together with reverse osmosis.

Applications for nanofiltration are the purification of acids via the selective separation of metals, desalination, decolorization, concentration of process solutions, separation of COD.

Reverse osmosis

Reverse osmosis works on a different principle. It makes use of the physical law according to which molecules are evenly distributed in a liquid.

Raw water and pure water are separated by a semi-permeable membrane. Due to physics, the pure water would migrate to the raw water. Salt water, for example, attracts fresh water. If the pressure on the raw water side is now increased, the process is reversed: more pure water accumulates on the clean water side.

The process is often used for seawater desalination, but it is also suitable for filtering many other undesirable substances from the water, e.g. nitrate, nitrite, drug residues, viruses, bacteria, fungicides, herbicides, asbestos, hormones, germs, lime or uranium. All substances harmful to your health will be eliminated.

Advantages of membrane filtration


  • Can be used specifically with regard to certain substances
  • Complete removal of unwanted components
  • Can be used permanently
  • Very gentle

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