Carbon dioxide can revolutionize rooftop farming, here is the proof

A new way to boost the growth of plants in rooftop farms.
Rupendra Brahambhatt
The BIG GRO system.
The BIG GRO system.

Dr. Sarabeth Buckley

Humans constantly breathe out large amounts of CO2 and when we are inside a building for a period of time, it creates high concentrations of carbon dioxide inside the building. This CO2 is removed through a building's exhaust system.

Interestingly, a team of researchers from Boston University has proposed a system called BIG GRO in which excess CO2 from a building’s exhaust system can be utilized as a fertilizer to grow thriving rooftop gardens.

“Plants take in CO2 as a source of food and when they are exposed to lots of CO2, they will grow bigger than they would have otherwise. I grew plants at the end of a building's exhaust system on the rooftop to provide them with excess CO2,” lead author and postdoctoral research fellow at the University of Cambridge, Dr. Sarabeth Buckley told IE.

Dr. Buckley and her team employed BIG GRO to cultivate spinach and corn on the rooftop of a building located inside the Boston University campus. They noticed that when the plants were exposed to high concentrations of CO2, they grew bigger and healthier.

CO2 makes rooftop gardens more viable

Carbon dioxide can revolutionize rooftop farming, here is the proof
Plants grown on roof using the BIG GRO system.

According to the United States Environment Protection Agency (EPA), the practice of growing plants on a building’s roof has several ecological and financial benefits. A rooftop garden improves the air quality in an area, reduces a building’s carbon footprint, makes it more energy efficient by acting as an insulator, and also enhances water quality.

However, rooftop gardens are hard to manage since plants experience a lot of stress when they are grown on a building’s roof. Direct exposure to sunlight, rainfall, and wind affect their growth, and most of the time, either the plants die, or they grow unhealthy. Moreover, setting up a rooftop garden with adequate water and nutrient supply for plants has its own challenges.

The researchers noticed this problem, and while looking for a solution, they realized that the carbon dioxide supply can create favorable conditions for plants grown in rooftop gardens. Since CO2 is basically food for plants, has the power to amplify photosynthesis, and is abundant in urban settings as humans are always breathing it out. It could increase plant growth, make rooftop farms more successful, and therefore more viable options for installation on buildings.

Carbon dioxide can revolutionize rooftop farming, here is the proof
Dr. Sarabeth Buckley working on the BIG GRO system.

In order to test this theory, the researchers decided to grow spinach and corn plants by placing them near the CO2 exhaust vents on the roof of a building. They created a rooftop garden setup using various devices and technologies and named it BIG GRO.

While explaining the different elements of BIG GRO, Dr. Buckley said, “I tested a variety of application systems, but ended up using a relatively simple aluminum ramp to move the exhaust air towards the plants. I also used milk crates with felt liners designed by a company called Recover Green Roofs, based in Boston, to grow all of the plants. This is the primary method used in rooftop farms in Boston.”

She further added, “To monitor environmental conditions, I used HOBO loggers that were attached to the vents and fans and recorded conditions such as CO2 concentrations, temperature, and relative humidity every 5 minutes.”

The concentration of CO2 in the air that came out of the vents was 800 parts per million. Such concentrations are more than enough for supporting healthy plant growth. The researchers also grew some spinach and corn plants near the control fans (away from the CO2 vents) so that they could compare the differences in the growth of the plants.

The results of this experiment were in alignment with what the researchers expected. The corn and spinach plants placed near the vents grew two to three times larger in size than the ones which were grown near the control fans. The researchers also realized that wind speed also played a significant role in plant growth.

For instance, high wind speed from the vent had a negative impact on plant growth. Therefore, in a system like BIG GRO, along with CO2 concentration, the wind is also required to be maintained at optimum levels.

What is the importance of systems like BIG GRO?

Carbon dioxide can revolutionize rooftop farming, here is the proof
Plants receiving CO2 from the vents.

According to Dr. Buckley, if BIG GRO is able to create a more hospitable environment for plants in rooftop gardens and allow them to grow larger, it could make rooftop gardens a more viable option for building owners who don't want to invest in an expensive green roof. This could lead to increased installation of rooftop farms, which provide various benefits ranging from heat management to energy savings and improving the overall quality of life.

However, BIG GRO's exhaust air application system needs to be optimized before it becomes a viable and mainstream technology. During their study, the researchers only grew plants directly around the vents, but ideally, people should be able to grow plants at a larger distance from the vent and still receive the same benefits.

Moreover, they also need to test the effectiveness of BIG GRO for various other plants and in different rooftop settings. Dr. Buckley plans to test and further develop BIG GRO in New York. She would like to help increase production in the many rooftop farms that already exist and the overall amount of rooftop gardens in NYC.

The study is published in the journal Frontiers in Sustainable Food Systems.

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