- The term "bio filter" encompasses many diverse organic air and water filtration techniques, including bioswales, slow sand filters and green walls. A bioswale is a bio filter that uses a drainage slope filled with compost to remove and purify surface runoff from a parking lot or other industrialized area. Slow sand filters also treat surface runoff by using gravitational pull to move water through a small sand pit infused with bacteria, fungi and protozoa that naturally purify. Green walls, also called vertical gardens, are structures that are covered in vegetation for the purpose of cleansing the air and are often attached to sides of buildings.
- Regardless of their specifics, all bio filters work to remove the same basic pollutants that can contaminate water and air. These contaminants are broken into classes: inorganic contaminants, organic chemicals and pathogens. Inorganic contaminants include anything metallic that is potentially harmful, such as lead or cadmium, as well as phosphates and nitrates that often come from artificial fertilization techniques. Organic pollutants mainly consist of pesticides used for crop protection. Pathogens are arguably the most dangerous of the pollutant classes and encompass a range of organisms that cause disease in humans and animals.
- While there are passive air bio filtration systems, like green walls, there are also active methods that work in larger air circulation systems to cleanse the air. In these situations, the air is forcibly passed through a small tube coated with biofilm, a controlled community of helpful bacteria and protozoa. Pollutants are caught by the micro-organisms in the biofilm and are removed from the air. Air bio filters are used throughout the world, especially in businesses or factories where air pollution is a production byproduct, like pharmaceutical manufacturing, wood manufacturing, paint manufacturing and resin manufacturing.
- One of the most widely used water bio filtration techniques is the trickling filter, a multilayer system that uses gravity to move water through it. A trickling filter passes water through downward-sloping tiers of gravel, peat moss, rocks and foam to purify sewage and waste water and make it suitable for drinking. This method of filtration has been popular throughout Europe for over 200 years, with countries like England, France and Denmark still using it today.
- While bio filters are effective purification systems that are also good for the environment, they are still under investigation by scientists and health officials because the role of micro-organisms in bio filtration is not fully understood. However, the benefits of the system are universally agreed upon, and bio filtration is gaining popularity as a chemical purification alternative all around the world.
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