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

Abstract

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...

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

“…As the mixture of VOC species and quantity of emitted VOCs varies amongst different plant species [59], it is possible that differences in biogenic VOC emissions between the S. wallisii and S. podophyllum biofilters may have contributed to the interaction between light type and botanical biofilter species, influencing the rate of NO 2 decay. Additionally, botanical biofilters are also capable of filtering out a range of VOCs [33] and the degree to which various VOCs are filtered is dependent on the plant species present within the biofilter [35]. These traits may have also differentially influenced the VOC concentration profile within the flow reactor and therefore, it is possible that the VOC profile associated with each plant species may have had ramifications for the NO 2 decay rate constants of each of the botanical biofilters.…”

“…Several recent studies have reported that green wall systems, in particular active green walls, have a high capacity to phytoremediate several air pollutants including particulate matter (PM) [30,31] and VOCs [32,33]. Regarding green wall VOC removal, biodegradation of VOCs by the rhizospheric bacteria along with substrate adsorption are considered as the primary sinks for VOC removal [24,34], however, plant-associated effects also play a role in VOC removal [35]. In the current experiment, all treatments contained both plants and substrate as discriminating between the substrate and plant effects are of no interest in practical applications of this technology.…”

Active botanical biofiltration of air pollutants using Australian native plants

“…For the determination of VOC and PM removal efficiencies, a flow through chamber was used, previously described in Irga et al (2019). In brief, the modules were placed in a sealed Perspex chamber (0.6 m 3 ; 216 L).…”

“…To determine the native species VOC removal capacity the same method described in Irga et al (2019) was applied. In brief, gaseous benzene was used as the VOC in this experiment (solubility at 25 °C = ~ 1/71 g/L).…”

“…In a similar experiment conducted previously (Irga et al 2019), the VOC SPREs of 4 common ornamental species in active green walls were compared, also detecting species differences for both benzene and ethyl acetate removal efficiencies. The benzene removal efficiency range amongst species recorded by Irga et al (2019) was relatively consistent, with <15% variability amongst species, with SPRE ranging from 45.54-59.50%. The ornamental species, N. glabra, was found to have the highest benzene removal efficiency, likely due to its high leaf wax content.…”