Enhanced removal of heavy metals and metalloids by constructed wetlands: A review of approaches and mechanisms

Constructed wetlands (CWs) are increasingly employed to remediate heavy metal and metalloid (HMM)-polluted water. However, the disadvantages of HMM removal by conventional CWs (without enhancement), such as an unstable and un-predictable removal efficiency, hinder the reliability of this technology. The objective of this study was to review research on enhanced CWs for HMM removal. In particular, we performed a bibliometric analysis to evaluate research trends, crit-ical literature, and keyword evolution in recent years. Subsequently, we reviewed various enhanced approaches for the application of CWs for the removal of HMMs, including the use of improved substrates, aquatic macrophytes, microorgan-isms, bioelectrochemical coupling systems, hybrid CW, external additives, and operation parameters. Furthermore, the main mechanisms underlying HMM removal by these approaches are summarized. Our review clearly reveals that re-search on the remediation of HMM-polluted water via CW technology is receiving increased attention, with no apparent trends in topics. The selection of appropriate enhanced approaches or operation parameters as well as methodological im-provements should be based on the dominant environmental conditions of the CW column and removal mechanisms for the targeted HMMs. Based on the established literature, several suggestions are proposed to guide the optimization of the design and operation of efficient CWs for the treatment of HMM-polluted water.

Automated summary

This study reviewed the research on enhanced constructed wetlands (CWs) for the removal of heavy metals and metalloids (HMMs) from polluted water. A bibliometric analysis was performed to evaluate research trends, critical literature, and keyword evolution. The study found that research on CW technology for the remediation of HMM-polluted water is receiving increased attention, with no apparent trends in topics. Suggestions for optimizing the design and operation of efficient CWs for HMM-polluted water treatment are proposed based on the established literature.