A team of agricultural researchers at Boston University came up with the idea while brainstorming ways to make urban environments more sustainable. As cities become denser, humans require more resources, and climate change worsens, buildings will likely require modifications to serve multiple purposes and recycle resource byproducts. Busy lecture halls with indoor climate control systems, it turns out, are a perfect example of such modifications. The building’s exhaust contains high levels of CO2, which plants convert to energy during photosynthesis.
Rather than releasing that CO2 into the environment uncontrolled, the researchers thought to direct their building’s exhaust toward an experimental rooftop garden. The garden, nicknamed BIG GRO, contained beds of spinach and corn. While both are common edible plants, corn photosynthesizes in a way that requires less CO2 than spinach, allowing it to serve as a control while the spinach ideally revealed the system’s advantages and disadvantages.
Beds were placed close to exhaust vents with large fans directing the exhaust toward the plants. (The team also installed an additional control containing both vegetables, which did not receive any exhaust air at all but were similarly fanned.) For four and a half weeks, the researchers monitored the plants’ growth and leaf quantity. Then they harvested the fruits—er, vegetables—of their labor.
The plants that had been exposed to the building’s exhaust had grown up to four times larger than the plants placed next to a control fan. The spinach in particular had quadruple the biomass of its control; the corn, despite its own special brand of photosynthesis, had two to three times the biomass of its control. Though the corn’s growth causes the team to think the extra CO2 wasn’t the only reason their experiment succeeded, there’s now concrete reason to believe rooftop farms like BIG GRO could benefit from buildings’ otherwise wasted exhaust.
“We are hoping this could lead to the further development of this system and eventual implementation in rooftop gardens and farms,” said study lead Dr. Sarabeth Buckley in a statement. “They could provide a multitude of environmental and social benefits such as energy savings for the building, carbon drawdown, climate mitigation, urban heat reduction, local food production, community building opportunities, and aesthetic and mental health benefits.”