Phytoremediation of indoor air represents an innovative, cost-effective and eco-friendly strategy to control indoor air quality that could integrate more traditional methods (e.g. ventilation and source control), especially in non-industrial environments. Since the end of the ‘80s, it is known that simple potted plants used as passive biofilters can remove Volatile Organic Compounds (VOCs) from indoor air even at low concentrations. In the last thirty years, many studies were carried out to quantify the removal rates of specific plant species towards different VOCs and the removal efficiencies that can be obtained introducing plants in a closed environment. Nevertheless, there are no well-assessed methodologies yet.
Considering all the factors that influence indoor air quality is crucial to comprehensively assess potted plants' removal capacity in closed environments. Therefore, basic indoor air models have been expanded and integrated with plants' abatement effect in order to develop an original indoor air model suitable for this purpose. The model consists in a mass balance where VOC concentration depends on the volume considered, on the outdoor pollutant concentration and on the ventilation rate (Air Change per Hour, ACH). At the same time potential indoor sources, and removal rate (sink) due to potted plants are taken into account in the model. The novel depletion term introduced is function of the plant's leaf area and of the VOC removal rate per unit of leaf area. The latter is species-specific and must be derived from experimental studies.
A real-existing copy shop, a non-industrial environment of particular interest, was chosen as a case study. The model was first calibrated on the basis of available measured concentrations without plants and then applied to estimate the removal efficiency obtainable with a defined leaf area of Zamioculcas Zamiifolia on ethylbenzene, xylenes and styrene concentrations (contaminants typically emitted by copiers). The estimated removal efficiencies (0.23 - 4.14% range) show that the significance of plants' removal contribution is strongly related to ventilation, but also show that the model is able to capture main features involved in idoor air quality.
It can be concluded that the proposed model wants to be a step forward towards the rational use of potted plants in indoor air mitigation interventions. After defining the VOC to address and the plant species to use, it allows the evaluation of the impact of inserting a given leaf area in a defined indoor environment and the determination of the leaf area necessary to obtain a specific abatement efficiency. Moreover, it could also guide the necessary process of standardisation of the protocols in the field, especially for the experimentations in real environments.