A combined vertical flow constructed wetland-microbial fuel cell system with duckweed post treatment for sustainable...

The intensification of pig farming has increased the challenge of managing piggery wastewater, which poses serious risks of eutrophication as well as soil and groundwater contamination. This study presents a hybrid pilot-scale treatment system integrating a two-stage vertical flow constructed wetland-microbial fuel cell (VFCW-MFC) planted with Canna indica and a duckweed-based post-treatment unit for sustainable wastewater remediation and resource recovery. The CW-MFC achieved removal efficiencies of 77.94 ± 7.47% COD, 73.63 ± 7.47% TOC, 61.91 ± 7.90% phosphate, 62.50 ± 10.05% nitrate, 53.43 ± 5.72% TAN, and 56.30 ± 7.95% total nitrogen, while generating a peak open circuit voltage of 478 mV and a power density of 38.7 mW m⁻². Subsequent duckweed polishing significantly enhanced nutrient removal, achieving 95.20 ± 0.50% phosphate, 80.88 ± 5.28% TAN, 80.29 ± 2.48% nitrate, and 89.91 ± 3.79% TN removal, with moderate COD (23.55 ± 1.48%) and TOC (38.53 ± 1.61%) reductions. In contrast, duckweed cultivated directly in raw wastewater achieved lower nutrient removals (76.19% phosphate, 62.69% TAN, 80.37% nitrate, and 72.65% TN), despite comparable biomass growth, indicating that pretreatment improved wastewater treatability rather than plant productivity alone. Overall, the integrated system achieved 83.08 ± 7.47% COD, 83.79 ± 5.47% TOC, 98.13 ± 6.90% phosphate, 91.07 ± 5.72% TAN, 92.06 ± 10.05% nitrate, and 95.57 ± 7.95% TN removal. Duckweed cultivation yielded 23.91 ± 3.20 g of fresh biomass in treated effluent and 25.10 ± 2.85 g in raw wastewater (DR) over 4 days. Biomass grown in raw wastewater exhibited a higher crude protein content (34.07%), whereas duckweed cultivated in treated effluent showed greater starch accumulation (18.12%), demonstrating flexible valorization potential for feed or bioenergy applications. These findings demonstrate that integrating VFCW-MFC with duckweed post-treatment provides an energy-efficient and scalable strategy for decentralized piggery wastewater management within a circular resource recovery framework.