CO2 from buildings could be used to improve rooftop gardens

Waste CO2 from building exhaust could be repurposed and used to improve rooftop gardens, according to a new study by the University of Cambridge.

Rooftop farms and gardens have a range of environmental benefits, as they can cool the surrounding area, increase building insulation and improve air quality. However, the plants grown here are often smaller and less healthy because they are exposed to more wind and solar radiation and have less soil moisture.

As CO2 is vital for plant growth, a team of researchers tested whether waste CO2 from building ventilation systems could be used to boost rooftop gardens by growing corn and spinach on the roof of a building on the Boston University campus.

“We wanted to test whether there is an untapped resource inside buildings that could be used to grow taller plants on rooftop farms,” ​​said Dr Sarabeth Buckley, post-doctoral researcher at the Department of Plant Sciences from the University of Cambridge. “Creating more favorable conditions that increase growth could help make rooftop trusses more successful and therefore more viable options for installation on buildings.”

Spinach and corn use different photosynthesis pathways, with spinach using a C3 pathway which is more sensitive to high CO2 levels.

Spinach was expected to benefit more from the escape vents, while corn served as a control to see how the vents affected plant growth.

Large ventilators were also placed in front of other control plants, to gauge whether air movement from the vents was a contributing factor.

The researchers found that spinach grown next to the air vents had four times the biomass of spinach grown next to a control fan. Even when high winds reduced the size advantage, plants were still twice as tall as controls.

“Many aspects of this system still need to be determined before it can be implemented, such as the optimal air application design and the possible extent of enhanced growth effect,” Buckley warned. “Furthermore, there is a decrease in growth with increasing wind speed, so the optimum wind speed should be found and incorporated into the system design.”

However, it does not appear that the change in size was entirely due to the influx of CO2, as the maize, which should have benefited less, also grew two to three times larger than the control plants.

The team, which has published its work in Frontiers of sustainable food systemsthink the study has important implications for how waste CO2 could be used to improve plant growth.

“We hope this could lead to the further development of this system and its eventual implementation in rooftop gardens and farms,” Buckley said. “If this happens, we hope that more roof trusses will be installed. They could provide a host of environmental and social benefits such as building energy savings, carbon reduction, climate mitigation, urban heat reduction, local food production, community building opportunities and aesthetic and mental health benefits.


Marjorie N. McClure