Unlocking functional potential of underutilized macrophytes: a pyrolysis-based screening approach for resource recovery

Abstract Invasive aquatic macrophytes constitute a significant proportion of biomass waste in tropical and subtropical regions across the world, posing substantial ecological, economic, and public health challenges. Converting these invasive plants into biochar, a porous carbon-rich material, offers an economically viable and environmentally sustainable approach for managing large volumes of biomass waste while supporting the transition towards a circular bioeconomy. While terrestrial plant biomass-derived biochar is well-studied, aquatic biomass-derived biochar remains underexplored. The novelty of the current work lies in its detailed systematic comparative investigation into slow pyrolytic transformation of three underutilized invasive aquatic macrophytes viz., water hyacinth ( Pontederia crassipes ), water lettuce ( Pistia sp.) and duckweed ( Lemna sp.) into biochar. The work comprehensively evaluates the combined effect of process conditions (temperature and residence time) on yield, physicochemical properties, surface morphology, and surface area of biochar. The critical and decisive influence of slow pyrolysis conditions was reiterated for aquatic feedstock. Uniquely, the current study reported the highest surface area of 316.3 m² g − 1 at 700 °C with 1 h residence time for non-activated duckweed biochar, followed by second highest report of surface area (344.9 m² g − 1 ) of water hyacinth biochar derived at 700 °C with 1 h residence time. The study also highlights significant variations in biochar properties as a function of parent feedstock, despite their shared aquatic origin. Despite being a major invasive aquatic plant, water lettuce has received comparatively little scientific attention. This study is among the first to provide an in-depth analysis of the physicochemical properties of water lettuce derived biochar. This work bridges a critical knowledge gap in aquatic plant biomass-derived biochar production and proposes a sustainable waste-to-resource valorization strategy of converting biomass into high-value carbon materials for varied applications, aligned with circular economy and climate mitigation goals.