Abstract

Constructed wetlands (CWs) are consolidated technologies used for removing organic matter (OM) and nutrients (nitrogen (N) and phosphorus (P)) from wastewater. Recently, these systems have been implemented for treating wastewater under saline conditions. In this context, the aim of this study was to evaluate the effect of wastewater with different levels of salinity, expressed as electrical conductivity (EC), on the removal efficiencies of OM and on the growth of vegetation planted in CW mesocosms. For this, five horizontal subsurface flow constructed wetlands (HSSFs) planted with Cyperus papyrus were operated under different salinity levels: 1 (CW-C), 2.5 (CW-2.5), 5 (CW-5), 7.5 (CW-7.5) and 10 mS/cm (CW-10) using CW-C as a control system. To analyze the effects of different salinity levels, the removal efficiencies of chemical oxygen demand (COD) and biological oxygen demand (BOD5) were evaluated. Moreover, the growth characteristics of Cyperus papyrus were compared in the different CWs through the determination of chlorophyll concentration and nutrient contents in different plant tissues. The results of this study showed that the removal efficiencies of OM were above 50%. Regarding the effect of salinity on the removal of contaminants, the COD and BOD5 removals decreased 18% and 31%, respectively, from CW-C to CW-10 (p .05). The sodium (Na+) concentration in Cyperus papyrus increased 82% when the salinity increased from 1 (CW-C) to 10 mS/cm (CW-10). In contrast, the chlorophyll concentration decreased 17% with increasing salinity (from 1 to 10 mS/cm). Finally, the vegetation presented mechanisms of salt tolerance, mainly Na+ accumulation in plant tissues. Despite these results, the technology of CWs could be a feasible alternative for the treatment of saline wastewater improving the plant selection.