The in situ pilot-scale phytoremediation of airborne VOCs and particulate matter with an active green wall

Abstract

Atmospheric pollutant phytoremediation technologies, such as potted-plants and green walls, have been thoroughly tested in lab-scale experiments for their potential to remove air pollutants. The functional value of these technologies, however, is yet to be adequately assessed in situ, in 'high value' environments, where pollutant removal will provide the greatest occupant health benefits. Air pollution in countries such as China is a significant public health issue, and efficient air pollution control technologies are needed. This work used pilot-scale trials to test the capacity of potted-plants, a passive green wall and an active green wall (AGW) to remove particulate matter (PM) and total volatile organic compounds (TVOCs) from a room in a suburban residential house in Sydney, Australia, followed by an assessment of the AGW's potential to remove these pollutants from a classroom in Beijing. In the residential room; compared to potted-plants and the passive green wall, the AGW maintained TVOCs at significantly lower concentrations throughout the experimental period (average TVOC concentration 72.5% lower than the control), with a similar trend observed for PM. In the classroom, the AGW reduced the average TVOC concentration by ~28% over a 20 min testing period compared to levels with no green wall and a filtered HVAC system in operation. The average ambient PM concentration in the classroom with the HVAC system operating was 101.18 µg/m 3 , which was reduced by 42.6% by the AGW. With further empirical validation, AGWs may be implemented to efficiently clean indoor air through functional reductions in PM and TVOC concentrations.

An Assessment of the Suitability of Active Green Walls for NO2 Reduction in Green Buildings Using a Closed-Loop Flow Reactor

“…Comparatively, botanical biofilters process large volumes of air, treat a variety of air pollutants (i.e., VOCs, PM, and NO x ), and generally have a limited substrate depth (i.e., reduce the space occupied and maintain aesthetic appeal). In this regard, it is important that active green walls are considered within the context of their full functionality (i.e., VOC filtration [33,43], PM filtration [30,31], CO 2 reduction [40], enhanced humidity and temperature [36], biophilic benefits [68]) and not solely as phytoremediators of a limited number of pollutants.…”

“…Replicate biofilters were housed in open-ended poly vinyl chloride (PVC) pipe (88 mm internal diameter, 120 mm in length). Each PVC pipe contained a coconut husk-based growth substrate packed to a depth of 85 mm to represent a realistic active green wall substrate depth that would be sufficient to support plant growth, as has been tested in previous research [34,43]. Coconut husk is a favourable substrate for use as a growth substrate in botanical biofilters as it has not been associated with bioaerosol emissions [44], and has a demonstrated capacity to filter VOCs [33] and PM [30].…”

Active Botanical Biofiltration in Built Environment to Maintain Indoor Air Quality

“…However, different climate zones should be investigated (including hot and cold) to justify the applicability of indoor ABB systems along with the energy-saving potential. Two pilot-scale AGWs were tested in both residential housing and a classroom to assess the removal capacity of both total volatile organic compounds (TVOCs) and PM (Pettit et al, 2019a). Analysis of the investigated data confirmed the reduction of TVOC and PM concentrations to a level that the classroom's current HVAC system could not achieve in normal conditions.…”

“…This approach was defined as active botanical biofiltration (ABB) by Pettit et al (2018a) where Liewellyn and Dixon (2011) stated the system as the botanical indoor air biofilter (BIAB) (Llewellyn and Dixon, 2011;Pettit et al, 2018a). Moreover, researchers used several other nomenclatures to refer this same system such as an active living wall (ALW) or active green wall (AGW) system when they applied this technology to the existing living wall or green wall systems (here living wall and green wall both indicate the similar vertical greening system) (Irga et al, 2017a;Pettit et al, 2019a). So far, research has been carried out dealing with different aspects of ABB to reduce overall air pollutants, such as the impact of plant quantity and type; temperature and airflow; media substrates; plant nutrition and irrigation; and lighting.…”

The evolution of botanical biofilters: Developing practical phytoremediation of air pollution for the built environment

“…Due to the extreme variation amongst indoor environments, such as differently sized rooms, different layouts, different lighting conditions, different ventilation rates, different ambient air quality and different pollution sources, it is necessary to assess active green wall operation within a range of environments to truly understand whether these systems can make worthwhile improvements to the air quality of indoor environments. Nonetheless, the limited number of in situ studies that have been performed have indicated that active green walls can improve the air quality of at least some indoor environments [72]. In addition to indoor applications, commercial active green walls are currently being installed in outdoor environments in select urban centres around the globe and system performance in such environments and the removal of NOx and O3 remains an area of important future research [73].…”