A biological process where a microorganisms (bacteria or fungus) is used to remove pollutants and odour from a gaseous waste stream.  The air stream carrying teh pollutants passes through the packing bed where bio degradation takes places. The microorganism grow on the media and feed on the VOC and other pollutants on the waste stream and convert it to non-doourous compounds such as CO2 and H2O. Trickling filters and bio scrubbers rely on a bio film and the bacterial action in their recirculating waters.

Typical odour removal efficiency in biofilters range from 75% for highly hydrophobic odorants to 99% for water soluble odorants.

Biofilters are ideal where pollutant levels are relatively constant. If pollutant levels fluctuate greatly the bacteria population may not be sustainable and therefore may result in loss of efficiency.  Pre-treatment should be used if toxicity level exceeds the threshold of the micro-organisms. Pre-treatment especially via chemical scrubbers or water scrubbers are common to increase moisture and balance PH levels.

BioFilter material are categorized as inorganic media (sand, gravel, geotextile, different shapes of plastic media, glass beads, etc.) and organic media (peat, wood chips, coco shell fragments, compost, etc.). Inorganic media typically require less frequent replacement and may have lower back pressure. Organic media provide additional feed to the microorganisms and are typically lower cost.

Biofilters have the advantage of an enviornmentally friendly solution with no harmful chemicals or excessive energy requirements. The main disadvantage of biofilter is their sensitivity to variation in pollutant levels, PH, and humidity. The system must be frequently monitored and maintanined.

Open Bed biofilter monitoring includes detection of low flow zones using infrared cameras and determination of local biobed efficiency using static hood sampling and in-field olfactometry or in-lab olfactometry.

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