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, <i>Spathiphyllum Wallisi</i> and <i>Syngonium Podophyllum</i>, 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. Botanical biofilters have demonstrated promising <i>in-situ</i> results for reducing indoor and urban air pollutants. The current research highlights the air-cleaning potential a granular activated carbon-based growth substrate can add to botanical biofilters for the removal of NO₂, but not O₃. Under elevated NO₂ concentrations, a growth substrate composition of 50% GAC and coconut husk produced an average clean air delivery rate of 1013.0 ± 173.1 m³ ·h⁻¹ ·m⁻³ of the biofilter substrate, outperforming botanical biofilters without GAC that underwent the same testing conditions. Furthermore, insight has been provided into the adsorption characteristics of GAC within botanical biofilters.