Turning an invasive alien species into a valuable biomass: Anaerobic digestion of Rugulopteryx okamurae after thermal and new developed low-cost mechanical pretreatments

5 Figuras.-- 3 TablasThe invasive alien seaweed Rugulopteryx okamurae (R.o.) has spread quickly through the Mediterranean Sea causing an unprecedented ecological impact. A solution integrated into a circular economy model is needed in order to curb the negative effects of its presence. Anaerobic digestion (AD) is proposed as a feasible process able to transform biomass into renewable energy. Nevertheless, in order to improve the methane yield and surpass the drawbacks associated with AD processes, this research proposes a thermal pretreatment and a new developed method where the macroalgae is mechanically pretreated with zeolite. Chemical and microstructure characterization of the algal biomass after pretreatments involved scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR). The highest methane yields of 240 (28) and 250 (20) NLCH4 kg-1 VSadded were obtained with the new mechanical pretreatment and the thermal pretreatment at 120 °C for 45 min without zeolite, achieving a 35 % improvement against the non-pretreated algae. A direct relationship between the crystallinity index of the samples and methane production was observed. The experimental data of methane production versus time were found to be in accordance with both first-order kinetic and Transference Function mathematical models.The authors wish to express their gratitude to the Spanish Ministry of Science and Innovation for providing financial support through the project PID2020-114975RB-100/AEI/10.13039/5011000/11033. Assistant by Dr. Consuelo Cerrillos González on the SEM measurement and analysis is acknowledged. We also thank the CEPSA Foundation, Red Eléctrica de España (REE) and Port Authority of Algeciras Bay (APBA) for their additional financial support for the development of environmental monitoring campaigns for Rugulopteryx okamurae and for obtaining samples of this species used in this work.Peer reviewe