Active botanical biofilters for nitrogen dioxide and ozone removal using granular activated carbon

Botanical biofilters can remediate numerous air pollutants and show potential for the removal of indoor NO₂ and O₃. Granular Activated Carbon (GAC) is a promising new addition to botanical biofilter growth media, increasing efficiency in Volatile Organic Compound (VOC) remediation, but it remains untested for other gaseous pollutants. This work assessed the capacity of an active botanical biofilter with a GAC growth medium to filter gaseous NO₂ and O₃ within a closed-loop flow-through reactor. We incorporate the effects associated with two plant species, Spathiphyllum Wallisi and Syngonium Podophyllum, substrate moisture, and varying ratios of GAC to coco coir on pollutant removal efficiency. All GAC containing substrates exhibited exponential decay for NO_2, with a 50% GAC wetted substrate composition producing the peak decay rate (0.27 ± 0.048 ppb.s^-1) and Clean Air Delivery Rate (CADR) at 1013.0 ± 173.1 m³·h^-1·m^-3of biofilter substrate. All treatments demonstrated non-significant removal of elevated O₃, possibly due to higher concentrations tested in the current work. There was no difference in NO₂ and O₃ removal rates or CADR between the two-plant species. This work provides promising results for the use of GAC within an active botanical biofilter to improve the removal of high concentrations of NO₂.