Comparative performance of palm-, sedge-, and mixed-vegetation vertical flow constructed wetlands for municipal wastewater polishing

This study comparatively evaluates the performance of pilot-scale vertical flow constructed wetlands (VFCWs) planted with sedges (Cyperaceae), palms (Arecaceae), and mixed palm–sedge vegetation for tertiary polishing of municipal wastewater following conventional sewage treatment. Although constructed wetlands have been widely investigated for wastewater treatment, systematic comparisons of palm-based, sedge-based, and mixed vegetation systems under identical tropical operating conditions remain limited. Furthermore, information regarding the influence of vegetation configuration on nutrient polishing, particularly total Kjeldahl nitrogen (TKN) and total phosphorus (TP), is scarce. Municipal wastewater collected from the 339 MLD Amberpet Sewage Treatment Plant (STP), Hyderabad, India, was treated using three pilot-scale VFCW systems operated under identical substrate composition and controlled feeding conditions. Treatment performance was evaluated over five field trials for pH, turbidity, dissolved oxygen (DO), biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), total dissolved solids (TDS), TKN, and TP. Among the three vegetation configurations, the sedge-based wetland consistently exhibited the highest pollutant removal efficiencies, achieving average removals of 91.2% BOD, 90.3% COD, 96.8% TSS, 93.2% turbidity, 91.8% TKN, and approximately 80% TP, while palm-based and mixed vegetation systems showed comparatively lower treatment efficiencies. The constructed wetlands provided substantial improvement in effluent quality beyond that achieved by the existing STP, demonstrating their effectiveness as tertiary polishing systems for municipal wastewater. The treated effluent complied with the applicable Central Pollution Control Board (CPCB) discharge standards for key physicochemical parameters, including pH, BOD, COD, TSS, and dissolved oxygen, indicating its suitability for safe environmental discharge and potential non-potable reuse. Overall, the findings demonstrate that vegetation selection plays a critical role in VFCW performance and identify sedge-based systems as the most effective configuration among those investigated for decentralized municipal wastewater polishing under tropical Indian conditions.