Removal of pharmaceutical active compounds in wastewater by constructed wetlands: Performance and mechanisms

The occurrence of pharmaceutical active compounds (PhACs) in aquatic environments is a cause for concern due to potential adverse effects on human and ecosystem health. Constructed wetlands (CWs) are cost-efficient and sustainable wastewater treatment systems for the removal of these PhACs. The removal processes and mechanisms comprise a complex interplay of photodegradation, biodegradation, phytoremediation, and sorption. This review synthesized the current knowledge on CWs for the removal of 20 widely detected PhACs in wastewater. In addition, the major removal mechanisms and influencing factors are discussed, enabling comprehensive and critical understanding for optimizing the removal of PhACs in CWs. Consequently, potential strategies for intensifying CWs system performance for PhACs removal are discussed. Overall, the results of this review showed that CWs performance in the elimination of some pharmaceuticals was on a par with conventional wastewater treatment plants (WWTPs) and, for others, it was above par. Furthermore, the findings indicated that system design, operational, and environmental factors played important but highly variable roles in the removal of pharmaceuticals. Nonetheless, although CWs were proven to be a more cost-efficient and sustainable technology for pharmaceuticals removal than other engineered treatment systems, there were still several research gaps to be addressed, mainly including the fate of a broad range of emerging contaminants in CWs, identification of specific functional microorganisms, transformation pathways of specific pharmaceuticals, assessment of trans-formation products and the ecotoxicity evaluation of CWs effluents.