Developing design criteria for active green wall bioremediation performance: Growth media selection shapes plant physiology, water and air flow patterns

Emerging data indicates that incumbent mechanical/physio-chemical air handling systems inadequately address common indoor air quality (IAQ) problems, including elevated CO₂ levels and volatile organic compounds (VOCs), with compounding negative impacts to human health. Preliminary research suggests that active plant-based systems may synthetically address these challenges. However, in order to design system performance parameters, the significance of species selection and biogeochemical mechanisms of growth media design need further characterization towards an effective bioremediative interface with air handling systems. Here, through three different species across three different growth media designs, we investigate trade-offs between CO₂ sequestration through photosynthesis and CO₂ production by metabolically active root-zones (that may remediate VOCs). Across the species, hydroponic media produced 61% greater photosynthetic leaf area compared to organic media which produced 66% more root biomass. CO₂ concentration changes driven by differing plant and growth media (organic vs. hydroponic) treatments were measured within a semi-sealed chamber. Repeated estimations of net CO₂ concentrations throughout plant development revealed decreasing influxes of CO₂ within the chamber over time, indicating evolving photosynthesis/respiration balances. Multivariate analysis indicates growth media design, through impacts to water availability, air flow rates and plant development, was a more significant driver of bioremediation performance metrics than species selection.