Irga, PJ, Pettit, TJ & Torpy, FR 2018, 'The phytoremediation of indoor air pollution: a review on the technology development from the potted plant through to functional green wall biofilters', Reviews in Environmental Science and Bio/Technology.View/Download from: Publisher's site
Poor indoor air quality is a health problem of escalating magnitude, as communities become increasingly urbanised and people's behaviours change, lending to lives spent almost exclusively in indoor environments. The accumulation of, and continued exposure to, indoor air pollution has been shown to result in detrimental health outcomes. Particulate matter penetrating into the building, volatile organic compounds (VOCs) outgassing from synthetic materials and carbon dioxide from human respiration are the main contributors to these indoor air quality concerns. Whilst a range of physiochemical methods have been developed to remove contaminants from indoor air, all methods have high maintenance costs. Despite many years of study and substantial market demand, a well evidenced procedure for indoor air bioremediation for all applications is yet to be developed. This review presents the main aspects of using horticultural biotechnological tools for improving indoor air quality, and explores the history of the technology, from the humble potted plant through to active botanical biofiltration. Regarding the procedure of air purification by potted plants, many researchers and decades of work have confirmed that the plants remove CO2 through photosynthesis, degrade VOCs through the metabolic action of rhizospheric microbes, and can sequester particulate matter through a range of physical mechanisms. These benefits notwithstanding, there are practical barriers reducing the value of potted plants as standalone air cleaning devices. Recent technological advancements have led to the development of active botanical biofilters, or functional green walls, which are becoming increasingly efficient and have the potential for the functional mitigation of indoor air pollutant concentrations.
Indoor air quality has become a growing concern due to the increasing proportion of time people spend indoors, combined with reduced building ventilation rates resulting from an increasing awareness of building energy use. It has been well established that potted-plants can help to phytoremediate a diverse range of indoor air pollutants. In particular, a substantial body of literature has demonstrated the ability of the potted-plant system to remove volatile organic compounds (VOCs) from indoor air. These findings have largely originated from laboratory scale chamber experiments, with several studies drawing different conclusions regarding the primary VOC removal mechanism, and removal efficiencies. Advancements in indoor air phytoremediation technology, notably active botanical biofilters, can more effectively reduce the concentrations of multiple indoor air pollutants through the action of active airflow through a plant growing medium, along with vertically aligned plants which achieve a high leaf area density per unit of floor space. Despite variable system designs, systems available have clear potential to assist or replace existing mechanical ventilation systems for indoor air pollutant removal. Further research is needed to develop, test and confirm their effectiveness and safety before they can be functionally integrated in the broader built environment. The current article reviews the current state of active air phytoremediation technology, discusses the available botanical biofiltration systems, and identifies areas in need of development.
Pettit, T, Irga, PJ & Torpy, FR 2018, 'Functional green wall development for increasing air pollutant phytoremediation: Substrate development with coconut coir and activated carbon.', Journal of hazardous materials, vol. 360, pp. 594-603.View/Download from: UTS OPUS or Publisher's site
Functional green walls are gaining attention due to their air cleaning abilities, however the air cleaning capacity of these systems may be improved through substrate modification. This experiment investigated the capacity of several green wall media to filter a range of air pollutants. Media, consisting of differently sized coconut husk-based substrates, and with different ratios of activated carbon were evaluated through the use of scaled down model 'cassettes'. Tests were conducted assessing each substrate's ability to filter particulate matter, benzene, ethyl acetate and ambient total VOCs. While the particle size of coconut husk did not influence removal efficiency, the addition of activated carbon to coconut husk media improved the removal efficiency for all gaseous pollutants. Activated carbon as a medium component, however, inhibited the removal efficiency of particulate matter. Once the substrate concentration of activated carbon approached 50%, its gas remediation capacity became asymptotic, suggesting that a 50:50 composite medium provided the best VOC removal. In full-scale botanical biofilter modules, activated carbon-based substrates increased benzene removal, yet decreased particulate matter removal despite the addition of plants. The findings suggest that medium design should be target pollutant dependent, while further work is needed to establish plant viability in activated carbon-based media.
Pettit, T, Irga, PJ & Torpy, FR 2018, 'The in situ pilot-scale phytoremediation of airborne VOCs and particulate matter with an active green wall', Air Quality, Atmosphere and Health.View/Download from: Publisher's site
© 2018, Springer Nature B.V. 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 g/m3, 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.
Torpy, FR, Pettit, T & Irga, P 2018, 'Applied horticultural biotechnology for the mitigation of indoor air pollution', Journal of People, Plants, and Environment, vol. 21, no. 6.View/Download from: UTS OPUS
Exposure to indoor air pollution is an emerging world-wide problem, with growing evidence that it is a major cause of morbidity worldwide. Whilst most indoor air pollutants are of outdoor origin, these combine with a range of indoor sourced pollutants that may lead to high pollutant levels indoors. The pollutants of greatest concern are volatile organic compounds (VOCs) and particulate matter (PM), both of which are associated with a range of serious health problems. Whilst current buildings usually use ventilation with outdoor air to remove these pollutants, botanical systems are gaining recognition as an effective alternative. Whilst many years research has shown that traditional potted plants and their substrates are capable of removing VOCs effectively, they are inefficient at removing PM, and are limited in their pollutant removal rates by the need for pollutants to diffuse to the active pollutant removal components of these systems. Active botanical biofiltration, using green wall systems combined with mechanical fans to increase pollutant exposure to the plants and substrate, show greatly increased rates of pollutant removal for both VOCs, PM and also carbon dioxide (CO2). A developing body of research indicates that these systems can outperform existing technologies for indoor air pollutant removal, although further research is required before their use will become widespread. Whilst it is known that plant species selection and substrate characteristics can affect the performance of active botanical systems, optimal characteristics are yet to be identified. Once this research has been completed, it is proposed that active botanical biofiltration will provide a cheap and low energy use alternative to mechanical ventilations systems for the maintenance of indoor environmental quality.
Irga, PJ, Braun, JT, Douglas, ANJ, Pettit, T, Fujiwara, S, Burchett, MD & Torpy, FR 2017, 'The distribution of green walls and green roofs throughout Australia: Do policy instruments influence the frequency of projects?', Urban Forestry and Urban Greening, vol. 24, pp. 164-174.View/Download from: UTS OPUS or Publisher's site
© 2017 Elsevier GmbH Green roofs and green walls are gaining popularity as a means of mitigating a range of environmental impacts associated with urbanisation. Although this technology has been widely implemented in some parts of the world, uptake within Australia has been slow. This might be attributed to a range of factors, including a lack of awareness; a scarcity of urban green infrastructure policies; a lack of examples to give urban designers confidence in the technology; and perhaps also a limited number of professionals capable of installing green infrastructure systems. This paper researches the distribution of green wall and green roof projects in urban Australia, and the possible influence of local government policies and guidelines that have been designed to promote the increase of green infrastructure in Australia's cities. Differences were observed among project distributions and frequency, both within and between cities. In addition, councils that offered policy instruments and guidance tended to have more green wall and green roof projects than those which have no such policies in place. Compared to successful examples seen internationally, further policy implementation in Australia could increase the frequency of green infrastructure projects, indicating that governmental influence may play a substantial role in encouraging green infrastructure installation.
Pettit, T, Irga, PJ, Abdo, P & Torpy, FR 2017, 'Do the plants in functional green walls contribute to their ability to filter particulate matter?', Building and Environment, vol. 125, pp. 299-307.View/Download from: UTS OPUS or Publisher's site
© 2017 Elsevier Ltd Indoor air quality has become a growing concern as people are spending more time indoors, combined with the construction of highly sealed buildings that promote thermal efficiency. Particulate matter (PM) is a common indoor air pollutant, with exposure to high concentrations associated with several detrimental health outcomes. Active botanical biofilters or functional green walls are becoming increasingly efficient and have the potential to mitigate high suspended PM concentrations. These systems, however, require further development before they become competitive with industry standard in-room air filters. Whilst the plant growth substrate in active biofilters can act as a filter medium, it was previously not known whether the plant component of these systems played a function in PM filtration. This study thus examines the influence of the botanical component on active green wall PM single pass removal efficiency (SPRE), with a focus on evaluating the air filtration features of different plant species in green wall modules. All tested botanical biofilters outperformed biofilters that consisted only of substrate. Green walls using different plant species had different single pass removal efficiencies, with fern species recording the highest removal efficiencies across all measured particle sizes (Nephrolepis exaltata bostoniensis SPRE for PM 0.3-0.5 and PM 5-10 = 45.78% and 92.46% respectively). Higher removal efficiencies were associated with increased pressure drop across the biofilter. An assessment of plant morphological data suggested that the root structure of the plants strongly influenced removal efficiency. These findings demonstrate the potential to enhance active botanical biofiltration technology with appropriate plant species selection.