Performance and mechanisms of reactive substrates in constructed wetlands: Emerging contaminant removal and greenhouse gas mitigation-A comprehensive review

Emerging contaminants (ECs) comprise a diverse group of chemical species with complex structures and varying degrees of persistence, posing significant long-term environmental risks. Constructed wetlands (CWs) are increasingly recognized for their ability to remove ECs from various environmental matrices. Recent advancements in reactive substrates have demonstrated enhanced physicochemical properties, such as improved adsorption capacity, electrical conductivity, and redox potential. These advancements not only mitigate the adverse effects of trace ECs on microbial communities and plants in CWs but also enhance the stability of EC removal processes and reduce greenhouse gas (GHG) emissions. However, detailed reviews of the efficacy and mechanisms of reactive substrates in CWs for the removal of various ECs and the reduction of GHG emissions are still lacking. This review provides a comprehensive overview of the removal capabilities and mechanisms associated with four key reactive substrates: zeolite, biochar, manganese ore, and iron ore. The focus is on their effectiveness against antibiotic resistance genes (ARGs), persistent organic pollutants (POPs), endocrinedisrupting chemicals (EDCs), per- and polyfluoroalkyl substances (PFASs), and pharmaceuticals and personal care products (PPCPs). Additionally, the review examines the role of carbon-based and metal-based substrates in mitigating methane (CH4) and nitrous oxide (N2O) emissions within CWs, highlighting their effects and underlying mechanisms. This review offers valuable insights and guidance for achieving sustainable ECs treatment and GHG reduction in CWs.