The phytoremediation of indoor air pollution: a review on the technology development from the potted plant through to functional green wall biofilters

Pettit

et al. 2019

Environ Sci Pollut Res

Volatile organic compounds (VOCs) are of public concern due to their adverse health effects. Botanical air filtration is a promising technology for reducing indoor air contaminants, but the underlying mechanisms are not fully understood. This study assessed active botanical biofilters for their single-pass removal efficiency (SPRE) for benzene, ethyl acetate and ambient total volatile organic compounds (TVOC)s, at concentrations of in situ relevance. Biofilters containing four plant species (Chlorophytum orchidastrum, Nematanthus glabra, Nephrolepis cordifolia 'duffii' and Schefflera arboricola) were compared to discern whether plant selection influenced VOC SPRE. Amongst all tested plant species, benzene SPREs were between 45.54-59.50%, with N. glabra the most efficient. The botanical biofilters removed 32.36-91.19% of ethyl acetate, with C. orchidastrum and S. arboricola recording significantly higher ethyl acetate SPREs than N. glabra and N. cordifolia. These findings thus indicate that plant type influences botanical biofilter VOC removal. It is proposed that ethyl acetate SPREs were dependent on hydrophilic adsorbent sites, with increasing root surface area, root diameter and root mass all associated with increasing ethyl acetate SPRE. The high benzene SPRE of N. glabra is likely due to the high wax content in its leaf cuticles. The SPREs for the relatively low levels of ambient TVOCs were consistent amongst plant species, providing no evidence to suggest that in situ TVOC removal is influenced by plant choice. Nonetheless, as inter-species differences do exist for some VOCs, botanical biofilters using a mixture of plants is proposed. Keywords Air pollution; botanical biofilters; phytoremediation; green walls; VOCs 'active green walls', which utilise mechanical assistance to funnel air into the biofilter substrate, improves their bioremediation efficiency to the extent that functional air remediation is probable (Torpy et al. 2015). These systems may also be practical for large infrastructure use, given that they are accessible, robust, cost-effective and have a low-energy footprint. Although the available types of botanical biofiltration systems differ in design, they all use active airflow facilitated with devices such as impellers that increase the airflow across or through the systems and therefore allow larger volumes of air to be processed by the biofilter. Whilst there is a growing body of literature that demonstrates the air pollutant remediation capabilities of this technology (Pettit et al. 2019), to date, the potential for plant selection to enhance botanical biofilters ability to filter some of the more dangerous air pollutants is required. Plant selection is known to have an influence on VOC removal efficiency for static, potted-plant systems (e.g. Kim et al. 2010). Whilst the nature of the plant characteristics that determine these effects have yet to be resolved, there may be phylogenetic associations where certain groups of plants are more effective for the removal of certain forms of VOC (Ki...

Section: Discussionsupporting

confidence: 71%

Section: Introductionmentioning

confidence: 99%

Does plant species selection in functional active green walls influence VOC phytoremediation efficiency?

Pettit

et al. 2019

Environ Sci Pollut Res

“…Active green walls are a green technology that can simultaneously treat a large number of air pollutants at a relatively low cost. This technology builds upon the vast literature purporting the air phytoremediation potential of potted plants ( [24,[26][27][28], plus references therein). Whilst pollutant reduction by potted plants has been well described, for in situ use, such systems will be severely limited in their efficacy [29].…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2019

Nitrogen dioxide (NO 2 ) is a common urban air pollutant that is associated with several adverse human health effects from both short and long term exposure. Additionally, NO 2 is highly reactive and can influence the mixing ratios of nitrogen oxide (NO) and ozone (O 3 ). Active green walls can filter numerous air pollutants whilst using little energy, and are thus a candidate for inclusion in green buildings, however, the remediation of NO 2 by active green walls remains untested. This work assessed the capacity of replicate active green walls to filter NO 2 at both ambient and elevated concentrations within a closed-loop flow reactor, while the concentrations of NO and O 3 were simultaneously monitored. Comparisons of each pollutant's decay rate were made for green walls containing two plant species (Spathiphyllum wallisii and Syngonium podophyllum) and two lighting conditions (indoor and ultraviolet). Biofilter treatments for both plant species exhibited exponential decay for the biofiltration of all three pollutants at ambient concentrations. Furthermore, both treatments removed elevated concentrations of NO and NO 2 , (average NO 2 clean air delivery rate of 661.32 and 550.8 m 3 ·h −1 ·m −3 of biofilter substrate for the respective plant species), although plant species and lighting conditions influenced the degree of NO x removal. Elevated concentrations of NO x compromised the removal efficiency of O 3 . Whilst the current work provided evidence that effective filtration of NO x is possible with green wall technology, long-term experiments under in situ conditions are needed to establish practical removal rates and plant health effects from prolonged exposure to air pollution.

“…As a possible solution to mitigate poor indoor air quality, a large body of research has tested the capacity of potted-plants to clean VOCs from the indoor environment (Aydogan and Montoya 2011; Cruz et al 2014a;Cruz et al 2014b;Hörmann et al 2017;Hörmann et al 2018;Irga et al 2013;Orwell et al 2004;Sriprapat et al 2014;Sriprapat and Thiravetyan 2013;Teiri et al 2018;Treesubsuntorn et al 2013;Treesubsuntorn and Thiravetyan 2012;Wood et al 2002). The use of plants for indoor air remediation offers an economical and sustainable departure from conventional techniques such as adsorption filters, photocatalytic oxidation purifiers, and ozone generators, that are often expensive, remove a constrained range of VOCs, and can produce harmful by-products (Irga et al 2018). However, the existing experiments on potted-plant VOC removal have most commonly been limited to laboratory-scale chambers, and despite the high VOC removal rates documented in these studies, it has been proposed that their removal rates in situ may be of lower practical value (Irga et al 2013;Llewellyn and Dixon 2011), as the pollutant removal rate is dependent upon the rate at which polluted air can diffuse to the active components of the potted-plant microcosm.…”

Section: Introductionmentioning

confidence: 99%

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

Pettit

Torpy

2018

Air Qual Atmos Health

Self Cite

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.