What is a Biofilter?

A Biofilter is any group of microorganisms cultivated in a closed biomedia with the intention of purifying contaminated gases or liquids. How could a biological filter of this kind help purify harvested rainwater for example? One of the biggest points to harvesting rainwater is making absolute certain that the water is clean and pure enough to drink. Biofilters have been around as long as nature itself, but have become wide spread with the ever propelling of modern day technologies. In nature water purification occurs because one organisms waste is another organism’s food, and thereby sustaining the biosphere’s food web. Biofilters are usually a second or third stage of filtering, usually done following a mechanical filter, or series of mechanical filters. Once the basic concept of a biofilter is understood, the creative possibilities of building one become only as limited as the human imagination.

“Biofilter” comes from the term biological filter, which can trace its origins to the Greek words for life “bios” and thought “logos”, with the word filter having more recent meaning in the material “felt” used to stain liquids in the past. After pondering the etymology, a poetic linguist may say that biofilters are “living strainers”. Microorganisms that feed off of the impurities in a liquid or gas, and in this way producing energy to be consumed by other organisms in the food web. A biofilter will combine these basic principles of nature’s law in a more sustainable way by harmonizing humankinds distancing, artificial and ego intense glorifying technological advancements with billions of years of natural evolution. A biofilter incorporates the very essence of the third law of competition; when organisms learn to work together in order to survive in a niche.

The secret to sustainable water filtration systems such as micro organic biological filtration is: “let nature do all the work”. If microorganisms have air, water, food, then they will thrive. Some microorganisms live and swim freely in water, while others can skim to the surface for oxygen, while still others can be attached to rocks, pebbles, limestone, sand, and pretty much any hard surface, as well as straw and roots. In nature, processes, such as settlement and filtration usually occur through sand or soil. Microorganisms decompose and break down organic material into nutrients. The end result is a balanced food web of consumption and production.

Biofilters such as those that could be used in rainwater harvesting have mechanical filters like grates, wire mesh, sponges, brushes, sand, gravel and others that keep big things like leaves and twigs out as well as smaller ones that keep dust particles out only as a first stage. In second stages of most biofilters, for pond water, grey water treatment, and even blackwater management, the system chosen for biological filtration can vary as widely as those used in rainwater harvesting. Most commonly the upspout or downspout systems are chosen. In up spout filters, the water comes from below and gets in contact with the biomedia (pebbles, limestone rings, bones… etc.), which is home to microorganisms that eat any decomposing micro organic materials naturally and then storing the water or passing it on to another, more intense filtraion system, like activated carbon. Down spout filters work in a similar fashion, but usually have better primary filters, and recycle the water constantly back into the biofilter, or into others more refined as in the example of up spouts.

There are two main types of downspouts; trickle down (or drip systems) and flood systems. Trickle down systems work with pockets of air all throughout the biomedia, as the flow of water is random. The flood systems, on the other hand generally use a pump and their biomedia tend to move around constantly inside the biofilter chamber. Both systems are common in freshwater pond filters and saltwater aquariums, but if the water is to be consumable, it needs a finer drinking water biofiltration using multiple layers of sand and gravel (especially if the water comes from some untimely origin such as in the cases of wastewater management biofiltration systems). As is done in underground streams to purify the natural well spring, by running for miles and miles under the earth, until finally crystal clean drinking water comes flowing right out of the ground.

Sand and gravel can be as much a circuit of biomedia as those installed in top dollar aquarium pumped multi-system filters or even more highly evolved breakdown organisms, found in the ocean. The fact is however; biofilter microorganisms need a place to thrive! They need place that has “air”, “water” and “food”. Rainwater biofilters differ from other kinds of biofiltration systems because the water is already very clean, and needs very little to become drinkable, but if contaminated, these systems for being a hundred percent positive about the harvested rainwater, become far more important and sustainable in the long run than highly expensive activated carbon systems that leave ecological footprints.


Posted in Filters by Administrator on August 16, 2005.

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