Artificial wetlands are used in over 50 countries to sustainably treat wastewater. These constructed wetlands (CWs) make use of natural biogeochemical and physical processes to remove organic matter and nutrients, while providing co-benefits such as ecosystem services and recreation. However, their performance can be variable, as local weather conditions, wastewater composition and operation can affect contaminant removal. In this Review, we discuss the global application and distribution of CWs, and factors affecting their functioning. Based on data from 335 field-scale CWs, hybrid CWs (which use two or more types of CW during water treatment) are the most effective for water-quality improvement and greenhouse gas mitigation, removing 76%, 63% and 72% of organic matter, nitrogen and phosphorus, respectively (based on the median values). Plant species, substrate selection, and environmental and hydraulic conditions affect performance, with variations in contaminant removal performance mainly related to temperature, hydraulic residence time and pollutant loading rates. Pollutant removal and long-term performance of CWs can be enhanced through strategies such as artificial aeration, cold-resistant plant selection, electron donor supplementation and clogging repair. Engineers and scientists must work together to design and manage CWs, ideally maximizing their co-benefits alongside pollution control.
Organic matter and nutrient removal performance, greenhouse gas emission fluxes and variables that affect these factors in constructed wetlands (CWs) are described using a global database of 2,457 water-quality observations and 129 greenhouse gas measurements extracted from 244 peer-reviewed publications.
Field-scale CWs were used in over 50 countries globally during 2001–2021, mainly in Europe (38.8%), Asia (32.8%), North America (14.0%) and Africa (8.1%).
There are clear differences in organic and nutrient removal in different types of CWs; hybrid CWs show the best median removal efficiencies for chemical oxygen demand (75.7%), ammonia-nitrogen (72.1%), total nitrogen (63.4%) and total phosphorus (71.8%), respectively.
Hybrid CWs have lower nitrous oxide (median fluxes 1.4 mg m−2 d−1), methane (median fluxes 91.5 mg m−2 d−1) and carbon dioxide (median fluxes 4.6 g m−2 d−1) emissions; their global warming potential is the lowest of the CW types.
Future CW design and management should prioritize ecosystem services while balancing water pollutant removal and socioeconomic benefits.
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This work was carried out with the support of the National Natural Science Foundation of China (no. 51925803), National Key Research and Development Program of China (no. 2021YFC3200602), Shandong Province Natural Science Foundation (ZR2021YQ36), QiLu Young Scholar Start-up Foundation of Shandong University and Young Taishan Scholars Program of Shandong Province (no. 202103017).
The authors declare no competing interests.
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Wu, H., Wang, R., Yan, P. et al. Constructed wetlands for pollution control. Nat Rev Earth Environ (2023). https://doi.org/10.1038/s43017-023-00395-z