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Biological exhaust air cleaning is used whenever exhaust air has to be cleaned from volatile organic compounds (VOCs) and odours. Biofilters play a major role in this process. The polluted exhaust air is passed through a filter medium where the VOCs and odours are separated. Normally, this medium is an organic carrier material where microorganisms are grown on. They convert the VOCs and odours into non-critical components by means of their metabolism. Especially regarding the removal of odorous substances, biofilters are a very efficient and comparatively inexpensive way of biofiltration - with an efficiency of up to 99 %. BIOCAT-biofilters have a high degree of efficiency in a wide range of applications, even for exhaust air components that are difficult to dissolve in water.

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When it comes to filter material, there are a few points to consider. The filter material should have a large surface area. This ensures a good exchange rate between exhaust air and filter material and provides sufficient space for microorganisms to colonise. The filter material must be designed in such a way that it has a good water holding capacity. The colonised microorganisms are only viable in a moist environment.

In general, different filter materials are used in one batch. The reason for this: it ensures both a good stability of the filter bed and a larger surface. In addition, the added microorganisms must be sufficiently supplied with inorganic nutrients and trace elements, unless this is provided by the composition of the exhaust air. The temperature inside the biofilter system plays a decisive role as well. Temperatures between 5 °C and 40 °C are favourable for the microorganisms to work properly.

A regular changing of the filter material ensures that the filter effect always works perfectly. Depending on the material, it should be replaced every two to five years.



The BIOCAT-biofilters from Wessel-Umwelttechnik work on the basis of certain heterotrophic microorganisms. Microbial degradation with the help of oxygen converts pollutants and odours into naturally formed carbon dioxide and water. First of all, the harmful substances are accumulated on the surface of the carrier material, changing from the gas into a water phase, thus making them accessible to the microorganisms. The biofilter systems from Wessel Umwelttechnik are designed modular. Therefore, they can be extended if needed and be realised in a space-optimised way.


Biological exhaust air purification is a cost-effective and efficient solution for many companies and municipalities to achieve the legal clean gas values of TA Luft and other regulations such as BImSchV, BREF. Biofilters have proven themselves over many years in a wide range of applications.

The advantages of Wessel-BIOCAT-filters are:

  • High efficiency
  • High operational reliability
  • Low operating costs
  • Low investment costs
  • No secondary emissions such as additional CO2, CO, SO2, NOx, dioxin, etc.
  • Modular design and separate connection of individual segments


Biofilters are suitable for exhaust air cleaning for almost all industrial sectors and municipal applications, as long as the pollutants contained in the exhaust air are water-soluble and non-toxic for the microorganisms added. These include, among others:

  • Animal feed production plants
  • Biogas plants
  • Waste treatment plants
  • Rendering plants
  • Slaughterhouses
  • Agricultural holdings
  • Food processing and luxury food industry
  • Chemical industry
  • Pharmaceutical industry
  • Automotive and supplier industry
  • Rubber processing industry
  • Semiconductor industry
  • Plastics processing industry



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