Effect of Soilless Substrate Volumetric Water Content on Particulate Matter Reduction in a Plant-Based Biofilter System

Background and objective: This study was conducted to quantify the reduction of particulate matter (PM) through a plant-based biofilter system, with the moisture content of the soilless substrate set at at different levels to enable comparison.Methods: For the experiment, a biofilter system (0.054 m<sup>3</sup>) consisting of an upper part with plants and soilless substrate acting as a filter and a lower part incorporating a wind blower for air circulation was constructed. Four <i>Aglaonema commutatum</i> 'Snow white' were planted in the biofilter system. Volumetric water content (VWC, %) of the substrate was set at different levels between 10% to 40%. The initial PM concentration in the sealed glass chamber (5.88 m<sup>3</sup>) was set to 500 μg⋅m<sup>-3</sup>, and the changes in PM concentration were measured 15 minutes after operation of the biofilter system.Results: As the substrate VWC in the biofilter system increased, the amount of PM<sub>2.5</sub> and PM<sub>10</sub> reduction decreased, with a linear response (<i>p</i> < .001), mostly due to increased pressure drop (PD) and decreased airflow rate (AFR) of the biofilter system. As the substrate VWC increased (from 10% to 40%), the PD increased (from 0.040 to 0.118 kPa), and AFR decreased (from 112.7 to 76.8 m<sup>3</sup>⋅h<sup>-1</sup>).Conclusion: Consequently, as the substrate VWC increased from 10% to 40%, the PD of the air passing through the substrate increased and the AFR decreased, resulting in a significant decrease in the PM reduction efficiency. Further research is required to determine the optimal substrate VWC that is effective in reducing PM without increasing the PD, while maintaining the proper growth of the plants.