Up-flow floating surface constructed wetland for municipal wastewater treatment: A novel approach

To fulfil the gap between sewage generation and treatment capacity, innovative and compact wastewater treatment technologies are required. This study presents the design, development, and demonstration of a pilot-scale Up-flow Floating Surface Constructed Wetland (UFSCW) for municipal wastewater treatment. UFSCW integrates primary and secondary treatments in a compact system. The UFSCW operates on the principle of up-flow movement of wastewater, through a floating arrangement of media and wetland plants. It provides a reduction in the velocity of suspended solids and increase contact time between pollutants, microbial communities, and plant root zones. The system combines both suspended and attached growth processes with anaerobic and aerobic treatment in a single unit. The system was operated in three phases: without hanging media and wetland plants, with hanging media only, and with both hanging media and wetland plants, under varying HRTs (36 to 12 h). At an HRT of 24 h (Phase III), UFSCW achieved maximum removal efficiencies of TSS, COD, TN, and TP of 92%, 82%, 67%, and 71%, respectively. Among the evaluated plant species, vetiver grass (Chrysopogon zizanioides) demonstrated the highest nutrient uptake efficiency. Its deep and fibrous root network provided an extensive rhizosphere that supported microbial colonization and facilitated enhanced nitrogen and phosphorus removal. Compared to conventional constructed wetlands requiring 2-4 days HRT, the UFSCW achieved comparable organic and nutrient removal at significantly shorter retention times, demonstrating its suitability for decentralized and space-constrained urban applications. Furthermore, integration of a downstream planted substrate bed and a disinfection unit could enable consistent compliance with discharge standards and facilitate treated water reuse.