biofiltration is a pollution control technique using living material to capture and biologically degrade process pollutants. common uses include processing waste water, capturing harmful chemicals or silt from surface runoff, and microbiotic oxidation of contaminants in air. thumb|right|biofilter installation at a commercial composting facility. examples of biofiltration include; * bioswales, biostrips, biobags, bioscrubbers, and trickling filters * constructed wetlands and natural wetlands * slow sand filters * treatment ponds * green belts * living walls * riparian zones, riparian forests, bosques ==control of air pollution== when applied to air filtration and purification, biofilters use microorganisms to remove air pollution. the air flows through a packed bed and the pollutant transfers into a thin biofilm on the surface of the packing material. microorganisms, including bacteria and fungi are immobilized in the biofilm and degrade the pollutant. trickling filters and bioscrubbers rely on a biofilm and the bacterial action in their recirculating waters. the technology finds greatest application in treating malodorous compounds and water-soluble volatile organic compounds (vocs). industries employing the technology include food and animal products, off-gas from wastewater treatment facilities, pharmaceuticals, wood products manufacturing, paint and coatings application and manufacturing and resin manufacturing and application, etc. compounds treated are typically mixed vocs and various sulfur compounds, including hydrogen sulfide. very large airflows may be treated and although a large area (footprint) has typically been requiredâa large biofilter (>200,000 acfm) may occupy as much or more land than a football fieldâthis has been one of the principal drawbacks of the technology. engineered biofilters, designed and built since the early 1990s, have provided significant footprint reductions over the conventional flat-bed, organic media type. thumb|right| air cycle system at biosolids composting plant. large duct in foreground is exhaust air into biofilter shown in next photo  one of the main challenges to optimum biofilter operation is maintaining proper moisture throughout the system. the air is normally humidified before it enters the bed with a watering (spray) system, humidification chamber, bioscrubber, or biotrickling filter. properly maintained, a natural
Air_pollution_control_systems Biodegradable_waste_management Environmental_engineering Environmental_soil_science Volatile_organic_compound_abatement Waste_treatment_technology Water_filters