We all know that plants take in carbon dioxide and release oxygen. It's one reason to keep greenery around the house: to make the air more breathable. Less well-known is that plant roots also improve the air we breath. When roots are exposed to air, they absorb toxins like toluene and formaldehyde and break them down into more benign forms.
Two university teams are now exploiting this fact by building appliance-sized "biofilter" units. Researchers at Purdue University have created a Biowall that lives inside a home's heating, ventilation, and air conditioning system. Made up of stacked plants growing aeroponically, the wall reduces airborne nasties and could even help reduce energy costs if deployed fully.
The Biowall is based on research by Bill Wolverton, an ex-NASA scientist. In the 1970s, NASA realized that sealed space capsules could make astronauts sick if the air wasn't properly recycled. Wolverton looked into using plants for purification and built a 45-foot BioHome to demonstrate his designs. He's since published several books on the topic, and sells a Plant Purifier system he created.
In the past, American homes have been nothing like space ships. Drafty and inefficient, most people didn't need to worry about toxic build-up. Perversely, as homes have become better insulated, they've started to circulate air less effectively. Hence the need for new solutions.
The Purdue wall was originally part of a student team's entry into the Solar Decathlon in 2011 and has now been taken on as a standalone project by students and three faculty. It recently won an award from the U.S. Environmental Protection Agency and is likely to be featured in a show-home that the company Whirlpool is fitting out near Purdue's campus.
"If you had a biofilter inside the home to keep the air relatively clean, you could bring in less outside air and therefore save money," says Bill Hutzel, the professor who's overseeing the project. "In the right situation, where a living plant wall was both an aesthetic and functional component, you might have a marketable, viable product."
The plants include English Ivy and Golden Pothos and grow out of commercial filters that are sprayed with water and fertilizer. "The tricky thing to keep the roots moist enough, so they don't completely dry out," Hutzel says. The air, which comes through a home's return air duct, doesn't pass straight through but is kept there awhile, giving the wall time to work its magic. Tests so far have shown the ability to reduce volatile organic compounds by about 15%.
A team at Syracuse University has built a similar "botanical air filter." As well as reducing toxics, it reduced heating and cooling costs by 15%, according to one published study.
Commercial filters could do a similar job. But Hutzel points out you need to replace them at some point and dispose of something covered in nasty stuff. The plants actually metabolize the pollutants. "The way we're thinking about it is that the Biowall would be the equivalent of a self-cleaning filter," he says. "It would slowly rejuvenate itself over time."