The use of constructed wetlands (CWs) has become increasingly popular in pollutant removal in combined sewer overflows, while the performance in dealing with odor compounds in CWs has remained an open question. In this study, Tidal flow Wetland (TW), Iron-carbon Wetland (IW) and Tidal flow Iron-carbon Wetland (TIW) were parallel constructed, where novel substrates modified with iron-carbon and different hydrodynamics in optimizing removal efficiency were compared. The degradation kinetics of geosmin (GSM), a typical kind of odor compounds, were selected to indicate the removal efficiency. The biological features in different constructed wetlands were investigated, in terms of microbial community distribution, functional genes and metabolic pathways. In contrast to TW, IW and TIW exhibited enhanced performance in degrading of GSM. At the steady stage, 19.74% and 23.19% of the GSM was removed in a 24-hrs cycle for IW and TIW respectively. The degradation process followed the pseudo-first-order kinetics. Cyanobacteria, which produced GSM as parts of their metabolites, and Flavobacterium and Sphingomonas, which acted as the degrader on the other hand, together contributed to the variation of GSM concentration in the constructed wetlands. The adding of iron-carbon in the substrates increased the abundance of Flavobacterium and Sphingomonas, while decreased the growth of Cyanobacteria, and weakened the biosynthetic pathway of terpenoids. Tidal flow further enhanced the aerobic environment of the wetland and stimulates the metabolic activities of microorganisms, therefore enhanced the pathway of metabolism and degradation of odor compounds. Consequently, such combination further favored the degradation of GSM and the final removal efficiency.
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