Removal pathways of pharmaceuticals and personal care products within vertical flow constructed wetlands as a decentralized greywater treatment

Although vertical flow constructed wetlands (VFCWs) have already demonstrated good performance in removing pharmaceutical and personal care products (PPCPs) from greywater (GW), removal pathways such as soil adsorption, microorganism biodegradation and plant absorption still need further exploration. In this two-year study, removal pathways of PPCPs from synthetic GW were evaluated, for the first time, using six VFCWs planted with Phragmites australis and Iris pseudacorus and filled with expanded clay (85-95 % share) mixed with innovative admixtures (5-15 % share): zeolite and biologically activated biochars - i) from plant residues and ii) cellulose from toilet paper. The estimated retained mass of PPCPs in VFCWs, based on removal efficiency, showed high values for some compounds, such as the UV filter-Octocrylene (OC: 237.6 mg), which can be related to high inlet concentrations due to its octanol-water partition factor (log Kow: 7.53), affecting the phase distribution, and to analytical difficulties leading to high limit quantification value (LOQ: 100 ng L^-1), underestimating removal efficiency. Although hydrophobicity has proven to be an important factor in understanding the PPCP fate in VFCWs, substrate composition showed its relevance. The estimated accumulation of PPCPs in VFCWs, applying semi-quantitation approach, revealed their greater presence in the underground part, with at least 77 % of PPCP accumulation occurring through adsorption process in the rhizosphere and 23 % at depth. The complementary study on monitoring PPCPs in real GW and benchmarking VFCW treatment with centralized wastewater treatment showed that decentralized GW treatment can remove OC with at least 84 % efficiency.