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Elevated salinity inhibits nitrogen removal by changing the microbial community composition in constructed wetlands during the cold season
We investigated whether subsurface flow constructed wetlands (SSF-CWs) can remove nitrogen from saline wastewater and if salinity affected nitrogen removal during the cold season (average water temperature < 10°C). Eight Iris pseudacorus-planted SSF-CWs were fed with normal (salinity, 1.3‰–1.5‰) (CWP) or saline (salinity, 6.3‰–6.5‰) (CWP+) wastewater, while eight unplanted SSF-CWs were fed with normal (CWU) or saline wastewater (CWU+). The systems were run continuously at a hydraulic loading rate of 187.5 mm·d−1 and a hydraulic retention time of 4 days. The nitrogen removal efficiency, plant parameters, and bacterial abundance and community composition were measured. In CWP, 80% of ammonium-nitrogen (NH4+-N) and 52% of total nitrogen (TN) were removed. In contrast, the removal rates of NH4+-N and TN in CWP+ were reduced by 27% and 37%, respectively. Under the higher salinity, not only was there a decrease in plant biomass (32.1%) and nitrogen uptake (50.1%), but also reduced growth (37.8%), activity (68.0%), and oxygen release (62.9%) of roots. The bacterial community composition was also different in the elevated salinity. Elevated salinity is associated with lower nitrogen removal in SSF-CWs, which we speculate is a result of suppressed wetland macrophyte growth and activity, and changes in microbial community composition.
MF17171 Accepted 08 November 2017
© CSIRO 2017