The anaerobic digestion (AD) of biomass is a green technology with known environmental benefits for biogas generation. The biogas yield from existing substrates and the biodegradability of biomasses can be improved by conventional or novel enhancement techniques, such as the addition of iron-based nanoparticles (NPs). In this study, the effect of different concentrations of Fe₂O₃-based NPs on the AD of brown macroalga Sargassum spp. has been investigated by 30 days trials. The effect of NPs was evaluated at different concentrations. The control sample yielded a value of 80.25 ± 3.21 NmL_CH4/g_VS. When 5 mg/g _substrate and 10 mg/g _substrate of Fe₂O₃ NPs were added to the control sample, the yield increased by 24.07% and 26.97%, respectively. Instead, when 50 mg/g _substrate of Fe₂O₃ NPs was added to the control sample, a negative effect was observed, and the biomethane yield decreased by 38.97%. Therefore, low concentrations of Fe₂O₃ NPs favor the AD process, whereas high concentrations have an inhibitory effect. Direct interspecies electron transfer (DIET) via Fe₂O₃ NPs and their insolubility play an important role in facilitating the methanogenesis process during AD.

The collection and use of Sargassum spp. as feedstock for the production of valuable products such as biomethane by anaerobic digestion (AD) would mitigate the negative impact of the blooms and the costs related to waste management in the Dominican Republic. In this work, the effect of the particle size of pelagic Sargassum spp. biomass, as a result of mechanical pretreatments, on the biomethanation was determined. The granulometric analysis of the mechanically pre-treated biomass was carried out using a Mastersize2000. The Biochemical Methane Potential (BMP) of the samples was determined using an Automatic Potential System Test II (AMPTS^® II). The kinetic parameters of the reaction were scientifically evaluated by using First order kinetic Model and modified Gompertz Model. The granulometric analysis showed a monomodal distribution on crushed biomass (505 µm) and a bimodal distribution on the milling sample (107 µm). The bimodal biomass means the biomass is characterized by the presence of fine and large particles. We observed that BMP increased by 78.85% when particles were reduced from 50,000 µm to 505 µm and by 73.61% when particles were reduced from 50,000 µm to 107 µm. A low methane yield from the milling biomass (107 µm) compared to the crushed biomass (505 µm) could be related to the excessive reduction of particle size. The fine particles are subject to the formation of aggregates and consequently, the contact area between the algae cells and the microorganisms that operate the anaerobic digestion process decreases.

In the present work, alkaline transesterification converted waste household cooking oil into biodiesel, a renewable alternative to fossil fuels. After characterising oil and choosing the independent variables of the reaction (methanol-to-oil molar ratio, catalyst concentration, temperature, and stirring), three dependent variables were selected to analyse biodiesel production globally, considering technical, energetic and environmental aspects. Therefore, biodiesel yield, energy intensity, and green chemistry balance were chosen as responses. This work considered four normalised green metrics with the best values close to 100 % to calculate the green chemistry balance and the "greenness" of the reaction, providing a comprehensive view of the sustainability of biodiesel production. After obtaining an experimental plan using a central composite design, the process responses under different operating conditions were assessed. The optimal conditions were obtained by response surface methodology and optimisation tools in both a single-criterion approach for each response and a multi-objective approach. Moreover, the analysis of variance was performed to determine the significance of quadratic models and the effects of independent factors on each response. When the three responses were simultaneously optimised, the results showed a maximum ester yield of 83.3 %, minimum energy intensity of 10.2 MJ/kg, and maximum green chemistry balance of 81.4 % at methanol to oil molar ratio of 3, KOH catalyst concentration of 1.3 wt%, temperature of 50.7 °C and stirring of 350 rpm. Nevertheless, different results were obtained when a single performance criterion was used, indicating the importance of a global multi-objective approach to the process involving green chemistry principles and process performance optimisation.

Purpose The collection and use of Sargassum spp. as feedstock for the production of valuable products such as biomethane by anaerobic digestion (AD) would mitigate the negative impact of the blooms and the costs related to waste management in the Dominical Republic. Methods In this work, the effect of the particle size of pelagic Sargassum spp. biomass, as a result of mechanical pretreatments, on the biomethanation was determined. The Biochemical Methane Potential (BMP) of the samples was determined using an Automatic Potential System Test II (AMPTS® II). The kinetic parameters of the reaction were scientifically evaluated by using First order kinetic Model and modified Gompertz Model. Results We observed that BMP increased by 78.85% when particles were reduced from 50000 µm to 505 µm and by 73.61% when particles were reduced from 50000 µm to 107 µm. Conclusion A low methane yield from biomass S.3 compared to S.2 could be related to the excessive reduction of particle size. The fine particles are subject to the formation of aggregates and consequently, the contact area between the algae cells and the microorganisms that operate the anaerobic digestion process decreases.

Posidonia oceanica (P. oceanica) is a key marine seagrass that provides essential ecosystem services but managing its stranded biomass (banquettes) poses a challenge to local authorities due to high disposal costs. This review examines the ecological and bioenergetic potential of P. Oceanica, focusing on the Calabria region. Through the analysis of regional monitoring data (ARPACAL) and a comprehensive review of the literature on anaerobic digestion (AD) processes, the study analyzes the transition from waste to resource. The results highlight a worrying regression of Calabrian meadows due to siltation and high burial-induced mortality. Chemically, the biomass is characterized by high recalcitrance (lignin > 34%) and an unbalanced C/N ratio (~153), which limits the efficiency of standard AD. However, the review demonstrates that acidic thermochemical pretreatment (132 °C with 0.4% HCl) can increase methane yields by up to 575%, while co-digestion with nitrogenous substrates further stabilizes the process. The study concludes that, although technical challenges such as reactor corrosion and sediment loss remain, the transformation of P. oceanica into biomethane represents a technologically potential route toward a circular Blue Economy, provided that operational and economic trade-offs are carefully balanced. Adopting the “Ecological Beach” model could enable sustainable coastal protection while unlocking prospective renewable energy potential.