Air biofiltration works by passing contaminated air through a bed of material where microorganisms break down pollutants.
Air biofiltration is an environmentally friendly technology primarily used to treat odorous and contaminated air, such as that vented from mechanically ventilated livestock buildings. It relies on natural biological processes to clean the air before it is released into the atmosphere.
The Core Mechanism
The fundamental principle is quite simple, leveraging the power of microbes.
- Creating the Bed: A bed of biological material, normally wood chips, is created within a contained structure. This material, often called the filter media, provides a large surface area and a suitable habitat for microorganisms. Common media include wood chips, compost, bark, peat, or a mixture of these.
- Air Flow: The ventilation air flows through the material. This flow brings the airborne contaminants (like gases and odors) into contact with the biological media and the microbes living on it.
- Microbial Absorption and Degradation: Gases are absorbed by cultures of microbes that develop within the bed. These microbes, typically bacteria and fungi, live in a thin layer of water (a biofilm) that coats the media particles. When the pollutant gases dissolve into this water layer, the microbes consume them as a food source, converting them into harmless substances like carbon dioxide and water through metabolic processes.
How Pollutants are Removed
The process involves several steps:
- Mass Transfer: Pollutants in the air stream transfer from the gas phase to the liquid phase (the biofilm on the media). This requires the gases to be water-soluble.
- Absorption: The gases dissolve into the water layer.
- Biodegradation: Microorganisms within the biofilm metabolize the dissolved pollutants. This is the core of the biofiltration process.
Where Biofilters Are Used
As mentioned in the reference, biofilters are commonly used on mechanically ventilation livestock buildings to treat the ventilation air. This helps reduce odors, ammonia, hydrogen sulfide, and other volatile organic compounds (VOCs) released from animal waste, improving air quality around the facility.
Key Components of a Biofilter System
- Filter Bed: The heart of the system, containing the biological media.
- Media: The material providing surface area for microbes (e.g., wood chips).
- Support Structure: Holds the media in place.
- Air Distribution System: Ensures even flow of air through the media bed.
- Humidification System: Often used to keep the air moist, which is crucial for microbial activity and gas absorption.
- Drainage System: Removes excess water.
Air biofiltration is an effective and sustainable method for treating air pollution by utilizing natural microbial activity within a specialized filter bed.
