Articles techniques et présentations

Historically, indoor air quality (IAQ) has received less attention than outdoors, although people spend >90% of their time in the indoor environment. A major group of indoor air pollutants is volatile organic compounds (VOCs), which are detrimental to human health even at low concentrations. Conventional technologies, i.e., activated carbon filtration, are considered unsustainable and have been extensively studied in modeling. Botanical biofiltration is a more sustainable and robust technology that can remove VOCs from indoor environments, employing physical-chemical and biological mechanisms. A botanical biofilter consists of a substrate and a botanical compartment where bacteria are present; hence modeling the technology becomes challenging. Previous modeling work is based on one-dimensional mathematical models that only predict the concentration at the outlet of a botanical biofilter. Notably, these models were limited by the number of boundary conditions that can be applied to the botanical biofilter and indoor environment, which is very complex. The present work integrates a 3D mass transfer multiphysics model in COMSOL Multiphysics® to simulate the removal of VOCs in the indoor environment using botanical biofiltration. The indoor environment is represented as an air domain with two external boundaries to apply an inlet and outlet flow. An additional source of VOCs inside the air domain was also considered. Secondly, the botanical biofilter geometry is built inside the air domain consisting of two domains corresponding to the vegetation and the substrate compartment. They are defined as unsaturated porous media with a liquid, gas, and porous matrix. Dispersion and adsorption were also added as boundary conditions in the substrate.
The multiphysics coupling of “Reacting Flow, Diluted Species” was chosen to solve the problem as it combines the Chemical Reaction Engineering Module with the CFD Module. The first solves the diffusion-convection equation with additional terms/sinks to represent the reaction rate of the VOCs due to the botanical biofilter; the second module solves the k-ε Turbulent Flow Model. The VOC concentration in the air domain and the botanical biofilter is visualized by streamline and surface plots. Also, the velocity and pressure are obtained. The present model can predict the time required to reach a zero VOC concentration in an indoor environment considering multiple boundary conditions. Such analysis is necessary to design and optimize an air purification technology. Parametric sweeps can be carried out to vary the model parameters like the botanical biofilter geometry, vegetation and substrate properties, mass transfer diffusion and dispersion coefficient, and the continuous or intermittent sources of VOCs. The latter leads to the optimization of botanical biofiltration.