Research progress on the application of manganese oxides in constructed wetlands: Efficiency, mechanisms, and prospects

As an eco-friendly wastewater treatment technology, constructed wetlands (CWs) hold significant application value in pollutant removal. Manganese oxides (MnOx) have emerged as a frontier research focus for CW substrate materials due to their unique redox properties, outstanding adsorption capacity, and remarkable catalytic activity. The fundamental physicochemical properties, sourcing pathways, and modification optimization strategies of MnOx substrates are reviewed. The removal efficacy and mechanisms of MnOx in CWs for organic contaminants, nitrogen, phosphorus, and heavy metals, are specifically elucidated. Furthermore, the regulatory role of MnOx in controlling greenhouse gas emissions within CWs is thoroughly analyzed. The ecological effects of MnOx on microbial community structure and plant growth within CWs are explored from a microecological perspective. However, the application of MnOx in CWs still faces scientific challenges, including unclear synergistic removal mechanisms for multiple pollutants, undefined pathways for greenhouse gas reduction, and insufficient understanding of electron transfer processes. This review provides theoretical foundations for optimizing MnOx-based substrates in CWs, offering significant guidance for advancing the technology toward higher efficiency, sustainability, and environmental friendliness.