Constructed wetlands (CWs) modified with adsorbents such as biochar, granular activated carbon (GAC), and natural zeolite were investigated to optimise the post-treatment of municipal wastewater effluent with a focus on the removal of organic and inorganic trace compounds. The study evaluated the removal efficiency of a wide range of persistent trace organic compounds (TrOCs), per- and polyfluoroalkyl substances (PFAS) and heavy metals (HMs) typically detected in municipal wastewater effluent concentrations ranging from ng/L to µg/L.A systematic review of the literature dealing with removal mechanisms such as sorption, ion exchange, co-precipitation, microbial degradation, and plant uptake was conducted to improve understanding of removal processes in CWs. Laboratory-scale batch and column experiments were conducted to determine the adsorption capacities of the selected media and to evaluate the influence of pH, particle size, and competitive ion presence on HM retention. In particular, competitive adsorption and remobilisation effects were examined for ammonium and HMs in natural zeolite. Pilot-scale experiments were carried out in vertical subsurface flow constructed wetlands (VSSF-CWs) modified with the selected adsorbents to evaluate real-world application under varying environmental conditions and hydraulic loading rates. The results demonstrated a better removal of bulk organics, nutrients, HMs and TrOCs, including PFAS compared to conventional wetlands, especially in GAC-containing CWs. Ecotoxicological assessments confirmed a significant reduction in effluent toxicity by the adsorbent-modified systems. Scanning electron microscopy coupled with energy dispersive x-ray (SEM-EDS) analysis revealed the contribution of individual adsorbents to overall contaminant retention and surface interactions. Compared to conventional CWs, the modified systems provide superior effluent quality with significant reduction of contaminants to levels that comply with the revised EU Urban Wastewater Treatment Directive 2024/3019 (UWWTD), which requires advanced removal of selected TrOCs. Adsorbent-modified constructed wetlands are cost-effective, energy-efficient and environmentally friendly solutions, suitable for centralised and decentralised wastewater treatment and reuse applications. Their implementation supports Sustainable Development Goal 6 by ensuring clean water and sanitation while enhancing ecosystem services. The optimum design and adsorbent selection depend on site-specific conditions, influent characteristics, and treatment objectives. Future research should focus on long-term performance, regeneration, and resource recovery strategies for used adsorbents, as well as detailed life cycle and cost assessments.
Luca Marco Ofiera (2025) studied this question.