Botanical Biofilters for the Phytofiltration of Urban Air Pollutants
- Publication Type:
- Thesis
- Issue Date:
- 2021
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Air quality is of emerging importance due to the rapid growth of urban populations that are exposed to air pollution in both indoor and outdoor environments. As a potential solution, active green walls or botanical biofilters have been developed to assist in the removal of air pollutants directly from environments where people live. Through the use of active airflow, these vertically orientated, botanical systems pass a contaminated airstream through the plant growth substrate and foliage to filter air pollutants. The work presented here explores the capacity of active green walls to filter air pollution through laboratory, indoor and outdoor studies. Firstly, laboratory-based experiments revealed that the single pass removal efficiency (SPRE) of different volatile organic compounds (VOCs) by active green walls is influenced by the VOC’s chemical properties, with average SPREs ranging from 19.76-96.34%. Modelling revealed that highly polar, small molecular weight molecules were removed with greatest efficiency. Secondly, pilot-scale trials assessed an active green wall’s pollutant removal within a classroom, with average total VOC and PM concentrations reduced by ~28% and ~42.6% respectively, over 30 min trial periods, compared to levels with no green wall but having a HVAC-filtration system in operation. Thirdly, botanical biofiltration of NO₂ was assessed at ambient and elevated concentrations within a closed-loop flow reactor, while the concentrations of NO and O₃ were simultaneously monitored. Biofilter treatments using two plant species (𝘚𝘱𝘢𝘵𝘩𝘪𝘱𝘩𝘺𝘭𝘭𝘶𝘮 𝘸𝘢𝘭𝘭𝘪𝘴𝘪𝘪 and 𝘚𝘺𝘯𝘨𝘰𝘯𝘪𝘶𝘮 𝘱𝘰𝘥𝘰𝘱𝘩𝘺𝘭𝘭𝘶𝘮) exhibited exponential decay for the biofiltration of all three pollutants at ambient concentrations. Furthermore, both treatments removed elevated concentrations of NO and NO₂. Subsequently, botanical biofilters were field-assessed for the filtration of traffic associated air pollutants – NO₂, O₃ and PM₂.₅ – from roadside ambient air in Sydney, Australia. Over two six-month research campaigns, all of the tested systems filtered NO₂, O₃ and PM₂.₅ with average SPREs of up to 71.5%, 28.1% and 22.1% respectively. Clean air delivery rates of up to 121 m³/h, 50 m³/h and 40 m³/h per m² of active green wall were achieved for the three pollutants respectively, with pollutant removal efficiency positively correlated with their ambient concentrations. An additional trial identified that active green walls filtered elevated air pollutant concentrations associated with the 𝘉𝘭𝘢𝘤𝘬 𝘚𝘶𝘮𝘮𝘦𝘳 wildfires, with average SPREs of 63.17%, 38.79% and 24.84% for NO₂, O₃ and PM₂.₅ respectively. These cumulative findings reveal that active green walls may play an important role in enhancing air quality and reducing air pollution exposure.
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