Aquatic plant Nymphaea mexicana as a viable feedstock for second-generation biofuel production

Every year several thousand metric tons of macrophytic biomass is removed from water bodies and discarded without any further use. Valorizing this biomass into biofuels can be a way to help in mitigating the world’s rising energy demand. In the current study, firstly nitrate reductase (NR) activity and total chlorophyll content in six prevalent aquatic plants present in Dal Lake, Srinagar, India, were determined. The NR activity and total chlorophyll in Nymphaea mexicana were found to be 0.180 ± 0.037 µmol NO2 g−1FW h−1 and 0.973 ± 0.13 mg/g, respectively, significantly higher among all studied macrophytes. Concurrently, the area coverage of this plant in the lake was also assessed and this plant covered 3.86 km2, approximately 70% of the total area under aquatic vegetation in Dal Lake, determining its high growth rate. The high growth rate of this plant can be ascribed to its high NR activity and total chlorophyll than other studied plants. Then this plant’s potential for producing bioethanol and biodiesel was also assessed. For bioethanol production, dried biomass was hydrolyzed using different dilute sulfuric acid concentrations (1–5% v/v) at different temperatures (100–230 °C) for different time periods (1.5–4.5 h). Maximum reducing sugar yield of 410.07 ± 18.20 mg/g biomass was obtained at 3% acid concentration and 130 °C temperature after 3-h time interval. This condition was selected as the optimal condition for hydrolysis, and hydrolysate was then fermented by Saccharomyces cerevisiae to produce bioethanol. Ethanol yield of 160 mg/g biomass was obtained after 96 h of fermentation. For biodiesel production, the dried biomass was Soxhlet extracted to obtain crude lipid followed by transesterification. A crude lipid yield of 34% (w/w) was obtained using a methanol and diethyl ether (2:1 ratio) solvent system. FAME analysis of trans-esterified lipid through GC-FID showed C16:0, C18:0, C18:1, C18:2, and C18:3 as dominant fatty acids, commonly found in biodiesel. Therefore, based on the findings, it can be inferred that Nymphaea holds the potential to serve as a viable feedstock for biofuel production. However, delving further into the techno-economic and lifecycle analysis of these methods will play a pivotal role in facilitating the advancement of large-scale production. Graphical abstract