Air Biofilters Information
Air biofilters are air pollution control devices that use microorganisms to capture and biologically degrade air pollutants. The microorganisms oxidize volatile organic compounds (VOCs) and odorous compounds and convert them into carbon dioxide and water. They often treat malodorous compounds and water-soluble VOCs.
The biofiltration process includes degradation of compounds in the filter and a pre-treatment humidification system. Pollutants enter the pre-treatment system where humidity-enhanced wet deposition helps capture pollutants in a liquid phase. They are then flushed through the biofilter media where a thin, biological film surrounds each particle. The aerobic environment allows bacteria to oxidize the VOCs and odorous compounds and converts them into carbon dioxide and water.
When using air biofilters, the biggest challenge can be maintaining the correct amount of moisture throughout the system. Air is typically humidified before entering the filter bed with a watering system (sprayer), a humidification chamber, bioscrubber, or biotrickling filter.
Air biofilters may use organic packing media such as peat, vegetable mulch, or wood chips for humidification purposes, or a combined natural and synthetic component. Organic packing media typically has a lifespan of several years. Use of combined material systems containing a mix of synthetic and organic materials greatly increases life expectancy. Other options include:
- Ceramics/fiber mesh pads
- Bulk plastics / UV resistant polymers
Packing media is the most important consideration of air biofilters. It provides a surface for bacteria to colonize. The ideal packing media has a high specific surface area, high void fraction, low passage diameter, low maintenance cost, and is constructed from inert materials.
A high specific surface area increases the amount of space available for bacteria to colonize.
The void fraction relates to the flow rate. A higher void fraction decreases flow restriction and allows for a higher system throughput.
The free passage diameter is the maximum particle size that can pass through the system unobstructed. The free passage diameter must be small enough to cause interaction between microorganisms and VOCs or odorous compounds, although it must be large enough so that clogging or plugging does not occur.
Maintenance cost is another factor that can affect packing media selection and may be affected by media weight and service life.
Inert materials are non-corrosive, chemically resistant, and have a long decay life. The use of inert materials greatly extends the life of the packing media. UV resistance is another feature that should be considered when specifying packing media.
Air biofilters are common in wastewater applications, chemical plants, and oil well operations. Air biofilters are also employed by industries, such as food and drink, pharmaceuticals, and product manufacturing of wood, paint, coatings, and resins.
VDI 3477--Guidelines for the biodegradation of air pollutants by biofilters.