Organic Matter and Nutrient Removal Performance of Horizontal Subsurface Flow Constructed Wetlands Planted with Phragmite karka and Vetiveria zizanioide for Treating Municipal Wastewater

Three pilot horizontal subsurface flow constructed wetlands (HSSFCWs) were constructed, covered with a geomembrane and filled with gravel media. The study compared the performance of the three pilot HSSFCWs, two planted with Vetiveria zizanioide and Phragmite karka, and one without plants, and all containing aeration facilities in treating municipal wastewater. HSSFCWs were loaded at a hydraulic loading rate of 0.025 m/d and a maximum organic loading rate of 6.16 g BOD/m(2)d with a hydraulic retention time of 6 days. Results show that V. zizanioide had better removal efficiencies (TSS: 92.3%; BOD5: 92.0%; PO43-: 86.7%) than P. karka (TSS: 91.3%; BOD5: 90.5%; PO43-: 85.6%), whereas P. karka showed better removal efficiency of NH4+ (86%), NO3- (81.8%) and SO42- (91.7%) than V. zizanioide (NH4+: 83.4%; NO3-: 81.3%; SO42-: 90.5%). Removal rates in unplanted CWs were lower for all parameters: TSS (78%), BOD5 (73%), NH4+ (61.0%), NO3- (55.5%), PO43(67.6%), SO42- (78.1%). Higher removals of total coliform (3 log units) and Escherichia coli (2.4 log units) were obtained in the HSSFCW with plants compared to unplanted units (total coliform: 1.9 log units; Escherichia coli: 1.2 log units). Based on these findings, the treated water can be directly disposed into surface water bodies or used for irrigation as the concentrations of the pollutants are below the standard permissible limits of effluent discharge set by EEPA and WHO. Therefore, both V. zizanioide and P. karka are good candidates for remediation of wastewater by a constructed wetland system.