ALTERNATIVES TO PURIFY INDOOR AIR
The rapid growth of the population favors increasing energy demand and therefore of energy efficient solutions. One of the more efficient systems is the nature and one of the most important lungs of the earth are plants and microorganisms that surround it. The bio-technology and bio-mimesis are immersed in science in this field and therefore with possible potential solutions.
NASA studied from 1973 the VOCs. Volatile Organic Compounds present in enclosed buildings, VOCs are gases that become inhalable vapor at room temperature, some have proven health effects, but others are highly toxic. NASA began testing common house plants and their ability to purify indoor air. A research paper by NASA found that “house plants can purify and renew the air inside our homes and workplaces, protecting us all from any side effects associated with prevalent toxins such as formaldehyde, ammonia and benzene. ” (XanaNatura , 2012).
A more benign addition to air filtration could be the use of houseplants. In addition to basic photosynthesis that removes carbon dioxide and returns oxygen to the air, plants can remove toxicants from air, soil, and water in at least two ways. First, they can metabolize some toxic chemicals, releasing harmless by-products, and second, they can incorporate toxicants such as heavy metals into plant tissues, thus sequestering them. (Claudio, 2011)
Given enough time nature can restore a site contaminated with organic compounds such as VOCs. One reason for this is that, frequently, materials such as VOCs that are toxic to some life are food for others. Most of the biological breakdown of VOCs is done by beneficial microbes, higher plants are not typically directly involved but facilitate the process . Some pollutant-degrading species are usually present and active in most environments, and the act of introducing the pollutant only increases their relative numbers and/or activity levels (Nedlaw Living Walls, 2012).
Advantages of using plants to clean air: Improved air quality, reduced energy consumption, no hazardous waste, disposal issues and Aesthetic appeal. (Darlington, 2001)
REMOVING CONTAMINANTS WITH NATURAL PROCESSES
The indoor air biofilter system works by employing technology that is an adaptation of two separate industrial processes:
1. Biofiltration. In this process, a contaminated air or water stream is passed through a biologically active substrate where beneficial microbes use the pollutants—such as VOCs—as their food source. Nothing accumulates within the biofiltration system, however, since microbes degrade the contaminants into their benign constituents of carbon dioxide (CO2) and water.
2. Phytoremediation. This process has traditionally used green plants to facilitate the recovery of contaminated soils, a process typically used to clean-up contaminated brownfield sites. Using this same fundamental technology, plants can be indirectly involved in cleaning up contaminated indoor air by assisting in the growth and effectiveness of the beneficial microbes and creating the environment where they can thrive. (Arsenault, 2013) (Washington, 2012)
IMPROVE FILTERING CAPABILITY OF PLANTS
Just as ventilation can be realized through either mechanical or natural means, it is now possible to realize highly effective air filtration through natural processes that can be coupled with mechanical systems. Potted plants in a space are not capable of achieving the same or even similar results. The reason is because the removal of air contaminants is accomplished not by the leafy parts of the plants but by microbes that exist on the roots. In potted plants, the roots are obviously contained in soil which has little or no exposure to the air. Further, the pot itself is impermeable meaning that air will not flow through the sides of the pot. Even if it did, it would not likely be able to flow through the soil so it would never reach the roots or the microbes that could do the job of cleaning the air. Therefore, while potted plants may absorb some small amount of carbon dioxide and replace it with oxygen through photosynthesis, they will have little other impact on indoor air quality. And they will certainly not filter out contaminants. (Arsenault, 2013) (Washington, 2012).
For more than 30 years, B.C. “Bill” Wolverton, a retired civilian scientist for NASA, investigated the use of plants as air- and water-purifying systems for enclosed environments in space missions. Through his research, Wolverton found the air-cleaning capacity of houseplants can be improved exponentially by increasing air circulation to the roots of the plants, where symbiotic microorganisms help make the substances culled from air bioavailable to the plant.
Experiments conducted elsewhere by Stanley J. Kays and colleagues at the University of Georgia also documented the ability of different plant species to remove VOCs such as benzene, toluene, octane, and trichloroethylene. One indoor contaminant of particular concern is formaldehyde, which is released by many household products, among them pressed woods, some types of foam insulation, paper products, some paints and varnishes, and permanent-press fabrics. As Wolverton found earlier, these investigators also found that formaldehyde removal by plants was diffusion-limited. That means increasing the circulation of contaminated air through the root system and leaves improved the formaldehyde-removal effect. (Claudio, 2011).
IMPACT OF BIOFILTRATION ON INDOOR AIR QUALITY
Impact of biofiltration on IAQ. The graph presents two lines. The first line indicates concentration of VOCs in a space under a range of ventilation (typical ventilation). The concentrations are presented relative to those seen when the space is subjected to ventilation rates 7.5 litres per person per second. The second line is the relative concentration when the space is subjected to the same range of ventilation but the air in the space is also treated with a standard-sized biofilter (ventilation + biofilter). (Nedlaw Living Walls, 2012) (see table in images).
Arsenault, P. J. (2013). Indoor Air Biofilters Deliver Clean Air Naturally. Ontario, Canada: Sponsored by Nedlaw Living Walls Inc. http://continuingeducation.construction.com/crs.php?L=326&C=951.
Claudio, L. (2011). Planting Healthier Indoor Air. USA: Environ Health Perspect.
Darlington, A. B. (2001). Indoor Air Biofilters. Guelph, Ontario: http://www.ces.uoguelph.ca/posters/biofilter.pdf. Department of Plant Agriculture, University of Guelph.
Nedlaw Living Walls. (2012). Nedlaw Living Walls. Obtenido de Indoor Air Contaminants: http://www.naturaire.com/indoor-air-pollutants
Washington, W. (2012). LIVING WALL BIOFILTERS: PUTTING NATURE TO WORK CLEANING INDOOR AIR. Washington DC: National convention and design expotition. The american institute of architects.
XanaNatura . (2012). XanaNatura . Obtenido de http://xananatura.blogspot.com/2011/12/plantas-purificadoras-del-aire-i.html