Ageing process characterization of innovative substrates in vertical-flow constructed wetlands after treating greywater

Vertical flow constructed wetlands (VFCWs) have recently been adopted for surface water pollution mitigation and applied in various treatment types (e.g., stormwater, wastewater, etc.) and target pollutants. However, their longevity and sustainability have been questioned, as well as the use of novel substrates to improve removal performance. In this context, here, VFCWs filled with the innovative admixtures zeolite and biochar produced in a circular economy way (i.e., biochar from plant residues and from sewage cellulose), in the proportions of 5 and 15 % mixed with expanded clay, are tested to improve the removal efficiency of personal care products (PCPs) from greywater (GW). The ageing process of these substrates after treating GW was evaluated for the very first time by physicochemical characterization. Proximate analyses and other measurements, as well as the study of pollutant removal kinetics, were performed at different depths within the VFCWs and defined timeframe. In the dye removal adsorption test, biochar substrates showed higher removal than zeolite ones at the initial condition, with 15 % sewage cellulose-based biochar being the best. After GW treatment, the 1st sampling depth showed lower correlation (R²) for dye adsorption compared to other scenarios due to the possible greater abundance of microorganisms in the plant rhizosphere, which may have negatively affected the soil adsorption process. Nonetheless, as VFCWs have performed well in removing macropollutants and target PCPs from GW for over a year, it is likely that other removal mechanisms, such as biodegradation by microorganisms and uptake by plants played a significant role.