Long-term performance of eight green wall plants in removing xenobiotic organic compounds from greywater across varied operational conditions

Green walls present a novel on-site approach for greywater treatment and reuse in densely populated urban areas, addressing the critical need for sustainable water management. However, the challenge lies in understanding the effectiveness of processes that drive the removal of emerging contaminants, particularly xenobiotic organic compounds (XOCs) originating from the use of personal care products and household chemicals. Therefore, a year-long mesocosm study was conducted on a large-scale green wall system, incorporating eight distinct plant species, to provide a scientific understanding of how different plant species and operational conditions (hydraulic loading, dosing frequency, and drying periods) impact XOCs removal. Results showed >80 % removal of hydrophobic and positively charged XOCs under all conditions, primarily through media-driven hydrophobic and electrostatic interactions. However, the removal of hydrophilic and negatively charged XOCs varied across plant species and was significantly impacted under high hydraulic loading and prolonged drying periods (i.e., 14 days). The system demonstrated the ability to effectively remove XOCs from large volumes of greywater, up to 120 l/m 2 /day, provided greywater dosing is applied in pulses with intermittent drying in between. This study provides valuable insights into designing and operating green walls and similar nature-based solutions for effective removal of emerging contaminants from wastewater. • Hydrophobic and positively charged XOCs exceeded 80 % removal under all conditions. • Hydrophilic and negatively charged XOCs removal varied across plant species. • Plants with dense and hairy roots removed higher XOCs than those with thick roots. • Pulse dosing with intermittent drying improved XOCs removal under high loading. • Longer dry period (14-days) reduced XOCs removal in green wall due to plant stress.