Over the past few years our team has worked with researcher Corbin Sparks, Master's of Applied Science candidate, and his team at Toronto Metropolitan University (TMU) to conduct research on the efficiency of microbial communities to remove airborne pollutants. Our role in this research has been to simply provide the necessary testing equipment and allow the science to prove itself. The following article is pulled from an interview we conducted with Mr. Sparks on this project.

What facility are we in and where was the testing done? 

"Currently we're in Toronto Metropolitan University's Center for Urban Innovation Facility, and all of our testing was actually done in one of the labs just downstairs."

What is your research focus? 

"I've been researching the removal of Volatile Organic Compounds [VOCs], using an active green wall produced by New Earth Solutions, along with testing the microbial ecosystem that is present within that wall before and after they've been exposed to those volatile organic compounds."

"The literature suggests that there can be changes to the composition of the bacteria, fungi and yeast that are present within the roots over time. So this means that after each test I take a sample of the the water and a root swab, and I test what kind of bacteria, fungi, and yeast are present within the roots."

What is your thesis? 

"I'm working on is testing the VOC removal efficiency of an active green wall to determine how it's removing certain chemicals over time based on the microbes present in the plant roots. So these are things like bacteria, fungi, and yeasts, and essentially they're the ones that are going to be removing the chemicals from the air because their metabolism is so much faster than that of the plants. [The microbes] also have a wide enough range of food sources that they will actually be able to use those chemicals as foods, whereas some of the plants may not be able to break them down into energy."

"The plants provide a [structural] support along with the nutrients to support the microbes, but then the bacteria and fungi are the ones that will essentially eat those volatile compounds over time and just release CO2 and other less toxic gases back to the environment."

When you say "the release of CO2", there's a lot of information out there about how that may or may not be a concern for with people with plants. Can you explain whether that is a concern or why it's not? 

"The concern with having too much CO2 indoors is that over time it can, or in too high a concentration indoors CO2 leads to things like drowsiness and many other health concerns or conditions. But with the plants, because it's in a green wall, the plants are going to be absorbing that CO2 from the bacteria and fungi. So as the bacteria and fungi remove chemicals and produce CO2, the plants will happily take up that CO2 and produce fresh oxygen, effectively canceling out any additional CO2 produced by the green wall [as long as it has enough light for photosynthesis]."

What one question would you want to find the answer to as it pertains to your research? 

"One of the main questions that I'd like to find out through this research is how exactly the bacterial and fungal microbes are changing over time. So are there more of a specific species of bacteria or less of them over time after they've been exposed to those chemicals."

Could you describe some of the differences between the VOC removal capabilities with water only versus water plus plants? 

"Essentially, when the green wall is running just with the water, it means that there aren't going to be many microbes present within it. There would only be a small number from what was in the water to begin with. When you have plants in the wall, they're bringing their own small ecosystem of bacteria and fungi into the wall. So there would be more microbes that are able to remove a wider variety of chemicals from the air in the planted green wall versus just water alone."

"To add on to this, the removal of the chemicals when it's just the water isn't really due to biological processes. Most of the time it'll be due to the chemicals just depositing onto the surface of the green wall or of the test enclosure itself, or it'll be from the chemicals mixing into the water. That being said, most of the chemicals we tested don't mix into water very efficiently, so they would tend to stay in the air throughout the duration of the test."

Do you have any thoughts on the optimal plant selection for this technology?

"In terms of optimal plant selection, some researchers have looked into what types of plants to use. But a lot of these tests have mostly just been to discern whether or not an outdoor plant is better than an indoor plant."

"There was some research conducted in Australia a couple of years ago where they were testing outdoor plants that are native to Australia versus common indoor plants, things like Pothos Ivy. What they found is that the indoor plants performed better for removing volatile organic compounds than the outdoor plants. This is likely due to indoor plants being bred to grow indoors where they're naturally going to be exposed to more VOCs because indoor air generally has a higher concentrations than outdoor air. In a case of microevolution, indoor plants may have become better suited for removing volatile compounds faster just because they've been grown in these conditions."

Finally, have you received any recognition for the work you are doing?

"Yes, I was nominated for a scholarship from the Air and Waste Management Association of Ontario in 2022, where they actually brought me out to their annual conference. At the conference, I got to talk about the research and some of my early findings about the removal of VOCs, along with what food sources the microbes in the green wall were consuming after they'd been exposed to the VOCs."

Any final remarks?

"This research is exciting because it's going to add to the wealth of data that we have that active hydroponic green walls are able to remove chemicals at a fast enough rate that they can either supplement or replace air circulation systems in some cases. "