Optimizing plant biomass from constructed wetlands for biogas production within the water-energy-food nexus

• CW biomass is a viable feedstock for biogas, transforming waste into energy. • Methane yield is strongly influenced by plant maturity and storage time. • Combining bioenergy recovery with wastewater treatment boosts sustainability and climate resilience. As the global demand for sustainable energy solutions grows, Constructed Wetlands (CWs) are gaining recognition not only for their effectiveness in wastewater treatment but also for their untapped potential as bioenergy sources. This study explores the viability of CW-derived plant biomass for biogas production, evaluating how plant species, maturity stages, and storage durations can influence methane yield. Using biomass from a free water surface wetland in Italy, four plant species, e.g., Phragmites australis, Typha latifolia, Carex spp., and Iris pseudacorus , were analyzed through Biomethane Potential (BMP) tests at three storage intervals: i) immediate – t(0), ii) three months after harvesting – t(1), and iii) six months – t(2) after harvesting, respectively. Results indicate that biogas yield peaked at t(1) for all species, with Iris pseudacorus showing consistent performance over time, and low carbon-to-nitrogen (C/N) ratios correlating with higher methane output. While plant maturity and storage significantly affected volatile solids and gas production, not all decreases in solids translated to higher methane yields. These findings indicate that CW biomass holds potential as a renewable feedstock for biogas production, though further optimization and scale-up studies are needed to confirm its practical applicability. By aligning with the Water-Energy-Food Nexus and Nature-based Solutions (NbS), the research promotes integrated approaches to enhance resource recovery, reduce waste, and support climate resilience.