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Subsurface-flow constructed wetlands (SSF CWs), which include horizontal subsurface–flow constructed wetlands (HSSF CWs) and vertical subsurface–flow constructed wetlands (VSSF CWs), have become increasingly popular for the treatment of various waste streams such as wastewater, landfill leachate, and stormwater runoff. These wetlands utilize a variety of natural physical, chemical, and microbial processes to effectively remove contaminants. This article aims to provide valuable insights into the application of subsurface-flow wetlands for the treatment of stormwater runoff by collecting and reviewing relevant articles. Within the realm of stormwater contaminants, this review primarily focuses on nutrients, heavy metal, and per- and polyfluoroalkyl substances (PFAS), which are commonly found in stormwater runoff worldwide. The removal percentages of these contaminants vary across different studies, depending on factors such as the characteristics of the contaminants, the type and scale of the subsurface-flow wetland, as well as the selection of plants and substrates used. This study provides valuable insights into the various processes that significantly contribute to the removal of contaminants, including adsorption, plant uptake, and biodegradation. The removal percentage of PFAS ranges from 1% to 99% in constructed wetlands. The wide range of PFAS removal comes from differences between PFAS category, plant and soil type, wetland configuration, and matrix effects. Additionally, this paper brings attention to the current gaps and limitations present in the research conducted within this field. It is imperative to conduct further studies utilizing real-world or synthetic stormwater runoff to deepen our comprehension in this domain. Furthermore, considering that each category of PFAS possesses unique properties, conducting individual studies on each group becomes crucial to attain a comprehensive understanding of the behavior and transformation of PFAS in CWs. [ABSTRACT FROM AUTHOR]

[Display omitted] Per- and polyfluoroalkyl substances (PFAS) are present in landfill leachate, posing potential challenges to leachate disposal and treatment. This work represents the first study of a thin-water-film nonthermal plasma reactor for PFAS degradation in landfill leachate. Of the 30 PFAS measured in three raw leachates, 21 were above the detection limits. The removal percentage depended on the category of PFAS. For example, perfluorooctanoic acid PFOA (C8) had the highest removal percentage (77% as an average of the three leachates) of the perfluoroalkyl carboxylic acids (PFCAs) category. The removal percentage decreased when the carbon number increased from 8 to 11 and decreased from 8 to 4. The effects of various landfill leachate components, including sodium chloride, acetate, humic acids, pH, and surfactants, had no or minor impacts (<30%) on PFOA mineralization in synthetic samples. This might be explained by the plasma-generation and PFAS-degradation mainly occurring at the gas/liquid interface. Shorter-chain PFCAs were produced as intermediates of PFOA degradation, and shorter-chain PFCAs and perfluorosulfonic acids (PFSAs) were produced as intermediates of perfluorooctanesulfonic acid (PFOS). The concentrations of the intermediates decreased with decreasing carbon number, suggesting a stepwise removal of difluoromethylene (CF 2) in the degradation pathway. Potential PFAS species in the raw and treated leachates were identified at the molecular level through non-targeted Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The intermediates did not show accurate toxicity per Microtox bioassay. [ABSTRACT FROM AUTHOR]