Corresponding VDI guideline: VDI 3477

• Microbiological degradation
• Organic filter material: Natural degradation
• Homogeneous repartition and streaming of the air through the filter bed
• Integrated preconditioning
• High separation results / high efficiency
• Upgradeability (for variable crude gas amounts)
• Low pressure loss
• Corrosion resistant
• Weather resistant
• Low maintenance and running costs
• Easy overview and easy handling of the display

The biofilter materials available differ in flow properties and in their biological activity. The term "biologically active" includes several factors:

• The filter material provides a high inner surface offering a good settlement area for the microorganisms and allows a constant growth of the micro-biological flora.
• It provides almost any "consumables" to the microorganisms (like water, nutrients, nitrogen and phosphate containing minerals) necessary for a constant growth of the flora and the decomposition of the pollutants.
• A homogenous air repartition over the entire biofilter surface avoids dead zones and punctual overloading in the filter bed thus ensuring a constant removal efficiency of the pollutants.
• In additon to that, a homogenous air repartition also ensures a sufficient O2-supply to the microorganisms, which is in turn crucial for a complete degradation of the pollutants and a high cleaning performance.
• During operational breakdowns the microorganisms will subsist from the nutrients contained in the biofilter material itself.

The filter layer itself being an organic material is of course subject to a natural, biological decomposition. Under optimal process conditions the biofilter material offers a long lifetime and needs to be exchanged every 3-5 years only.

The disposal of the old filter material presents no problem at all since it can be reused in landscaping or composting afterwards. The possible filter material exchange has to be kept in mind at the design phase (driving access, maintenance openings) in order to guarantee the longterm operation of the biofilter.

The efficiency of the biofilter material and its bioflora depends on the operational safety of the pre-conditioning unit. Its proper function is therefore ensured by especially sophisticated measuring and control equipment. This is extremely important since a breakdown of the pre-conditioning would have negative effects not being reversible at all or to a limited extent only (possible consequences: drying out of the filter material, change of pH-value or aerosol deposition).

An external rehumidification of the filter material is therefore only possible to a limited extent: Irregular water absorption would lead to zones overwetting thus causing a considerable flow resistance.

Such over-wetted zones would not be flowed through efficiently by the waste air anymore. The degradation of the pollutants would consequently fail and lead to an anaerob, odour-intensive decomposition as a result of the produced oxygen deficit. The residual dry zones that would be easily flowed through and overloaded, would continue to dry out which is also known as "chimney effect".