Biofilter / Odor Control / Waste Air Treatment

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Definition of Biofilters and Description


  Biofiltration is an air pollution control technology which utilizes microorganisms to biologically degrade odors and other volatile air pollutants contained in waste air streams. The microorganisms exist on the surface and in a thin water film surrounding the surface of the biofilter material. During the biofiltration process the contaminated air is slowly pumped through the biofilter material. The pollutants are adsorbed by the filter material's surface, and absorbed into the water film. Simultaneously the microorganisms biologically consume i.e. metabolize the pollutants, producing energy, biomass, and metabolic end products, mainly CO2 and H2O. The biofiltration process results in a complete decomposition of the pollutants without creating hazardous byproducts.

Biofilters are technical applications that use the biofiltration process to remove odorous compounds and other air pollutants like volatile organic compounds (VOC) from waste air. The name "biofilter" may be confusing by the imagination of normal filters which simply separate pollutants from fluids or gases. In a biofilter the pollutants are "consumed" by the microorganisms and degraded into biomass, water and CO2. This allows the filter material to continuously regenerate itself. The term bio-catalyst or bio-reactor would therefore be more suitable, however the name biofilter is commonly accepted and used.


  The filter material which can be peat, cocos, tree bark or better root wood is adsorbing the odourous compŁounds resp. the pollutants of the waste air stream. Naturally microorganism on and in the filter material are going to degrade them more or less without residues.

Biofilters are applicated for example to clean odourous air streams of industries like paint shops, waste water treatment plants (WWTP), food and animal feedstuff industry or composting plants.

Biofilters are suitable for elimination of gaseous or volatile toxic organic aerosols. Detailed informations about applications and requirements of biofilters and biofilter systems are presented by the german regulations "VDI Richtlinie 3477 - Biofilter".

Indispensable for a good function of a biofilter is the providing of adequate physical and chemical conditions such as temperature, humidity, nutrient supply and pH-value. Only if these conditions are kept in a perfect status the microorganism will metabolize on a high level to degrade as much pollutants as possible.

Providing this needs distinct microbiological, technical and physical knowledge in projecting, planning and constructing biofilter plants. Just filling organic media onto a grid is the most simple but very sure not the best way to build a biofilter. Such "biofilters" will cause problems within short time or even get out of function.


  The easiest design of a biofilter is the age-old practice of covering landfills with soil. The odorous air rises through the layer of soil where microorganism degrade the odorous compounds. However to plan, design and build a biofilter that will continuously run reliably, it takes technical and microbiological expertise and experience. A crucial prerequisite for the successful functioning of biofilters is the creation and maintenance of suitable physical and chemical conditions for microorganism to thrive. This includes maintaining the right temperature, moisture, pH-value and amount of nutrients. Bioteg Biofilter Systems therefore consist of the following basic components:

     - Ventilator
     - Air humidifier (with integrated heating, if necessary)
     - Air distributor
     - Filter material
     - Control Panel