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

Surface runoff

Surface runoff is the water flow that occurs when soil is infiltrated to full capacity and excess water from rain, meltwater, or other sources flows over the land. This is a major component of the water cycle. Runoff that occurs on surfaces before reaching a channel is also called a nonpoint source...

, and microbiotic

Microbiology

Microbiology is the study of microorganisms, which are defined as any microscopic organism that comprises either a single cell , cell clusters or no cell at all . This includes eukaryotes, such as fungi and protists, and prokaryotes...

 oxidation of contaminants in air.

Examples of biofiltration include;

• Bioswale
  Bioswale
  Bioswales are landscape elements designed to remove silt and pollution from surface runoff water. They consist of a swaled drainage course with gently sloped sides and filled with vegetation, compost and/or riprap...
  
  s, Biostrips, Biobags, Bioscrubbers, and Trickling filter
  Trickling filter
  A trickling filter consists of a fixed bed of rocks, lava, coke, gravel, slag, polyurethane foam, sphagnum peat moss, ceramic, or plastic media over which sewage or other wastewater flows downward and causes a layer of microbial slime to grow, covering the bed of media...
  
  s
• Constructed wetland
  Constructed wetland
  A constructed wetland or wetpark is an artificial wetland, marsh or swamp created as a new or restored habitat for native and migratory wildlife, for anthropogenic discharge such as wastewater, stormwater runoff, or sewage treatment, for land reclamation after mining, refineries, or other...
  
  s and Natural wetlands
• Slow sand filter
  Slow sand filter
  Slow sand filters are used in water purification for treating raw water to produce a potable product. They are typically 1 to 2 metres deep, can be rectangular or cylindrical in cross section and are used primarily to treat surface water...
  
  s
• Treatment pond
  Treatment pond
  A treatment pond treats water fouled by anaerobic bacteria. It is used mainly by tree nurseries, dairy farms and other agricultural companies near horse or cattle sheds or barns...
  
  s
• Green belt
  Green belt
  A green belt or greenbelt is a policy and land use designation used in land use planning to retain areas of largely undeveloped, wild, or agricultural land surrounding or neighbouring urban areas. Similar concepts are greenways or green wedges which have a linear character and may run through an...
  
  s
• Living wall
  Living wall
  A green wall is a wall, either free-standing or part of a building, that is partially or completely covered with vegetation and, in some cases, soil or an inorganic growing medium. The concept of the green wall dates back to 600 BC with the Hanging Gardens of Babylon...
  
  s
• Riparian zone
  Riparian zone
  A riparian zone or riparian area is the interface between land and a river or stream. Riparian is also the proper nomenclature for one of the fifteen terrestrial biomes of the earth. Plant habitats and communities along the river margins and banks are called riparian vegetation, characterized by...
  
  s, Riparian forest
  Riparian forest
  A riparian forest is a forested area of land adjacent to a body of water such as a river, stream, pond, lake, marshland, estuary, canal, sink or reservoir. -Etymology:...
  
  s, Bosque
  Bosque
  Bosque is the name for areas of gallery forest found along the riparian flood plains of stream and river banks in the southwestern United States...
  
  s

When applied to air filtration and purification, biofilters use microorganisms to remove air pollution

Air pollution

Air pollution is the introduction of chemicals, particulate matter, or biological materials that cause harm or discomfort to humans or other living organisms, or cause damage to the natural environment or built environment, into the atmosphere....

.
The air flows through a packed bed and the pollutant transfers into a thin biofilm

Biofilm

A biofilm is an aggregate of microorganisms in which cells adhere to each other on a surface. These adherent cells are frequently embedded within a self-produced matrix of extracellular polymeric substance...

 on the surface of the packing material.