Efficiency of horizontal subsurface flow constructed wetlands cultivated with grasses of different root systems

Abstract

The objective of this study was to evaluate the influence of stoloniferous and fasciculated root systems, of Tifton 85 and vetiver grass respectively, on pollutant removal for primary treatment of sewage in horizontal subsurface flow constructed wetlands (HSSF-CWs). For this, three HSSF-CWs measuring 4 m × 1 m × 0.25 m, filling with gneiss gravel # 0 (D60 of 7.0 mm and 48.4% porosity) as substrate, were used. One unit was cultivated with Tifton 85 grass (HSSFT-CW), one with vetiver grass (HSSFV-CW) and one remained uncultivated (HSSFC-CW) as a control. Sewage was applied at a flow rate of 0.53–0.80 m3 d−1, corresponding to an organic loading rate of approximately 350 kg ha−1 d−1 (biochemical oxygen demand – BOD), which resulted in a hydraulic retention time of 0.6–0.9 day. The HSSFV-CW was more efficient than the HSSFC-CW in removing dissolved solids (measured as electrical conductivity) and reducing the total suspended solids (TSS), BOD5, turbidity and sodium concentration, while the HSSFT-CW was not superior in any way. The results indicate that cultivation of vetiver grass provided increased efficiency for removing pollutants from sewage when compared with Tifton 85-grass, in the HSSF-CW.