Collecting Sargassum spp. biomass and using it for the generation of renewable energy is a sustainable approach to mitigate the costs associated to this weed management. The biomethanation of this algal biomass with other organic waste to produce biogas promotes the integrated sustainable management of these materials while generating gaseous fuel for the tourism industry. The purpose of this work is to determine the percentage Sargassum spp. biomass during the anaerobic co-digestion of this brown algae with food waste that results in the best biogas composition, methane yield, production kinetics, and digestate. The biomethanation was conducted in 1200 L fed-batch and bench scale batch biodigestors and the kinetic parameters were estimated using the modified Gompertz model. The methane yield of Sargassum spp. and food waste combinations in 0.58 OLR at fed batch and 15 g/L organic load at batch were comparable. The methane yield produced in the 100% Sargassum spp. fed-batch anaerobic biodigester was 101.3 ± 23.6 N. L CH₄/kg, but up to 615.5 ± 78.4 N. L CH₄/kg in the 45% Sargassum spp. / 55% food waste biodigestor. The anaerobic co-digestion of Sargassum spp. and food waste in the batch system showed methane production rates as high as 14.6 ± 0.3 N.L CH₄/kg.day. Higher H₂S were detected in the biogas of the biodigesters fed with larger percentages of the Sargassum spp. with more than 5000 ppm during mono-digestion. Our results suggest that 55% Sargassum spp. and 45% food waste are the most promising feed combination under the studied conditions for the anaerobic co-digestion of these feedstock at larger scale.

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.

The anaerobic digestion of the invasive water hyacinth (Pontederia crassipes Mart.) from eutrophic water bodies could contribute to the sustainability of communities that have insecure energy sources. The optimization of critical process parameters, e.g., feed to inoculum ratio (F/I), temperature, supplementation, and inoculum acclimatization is important for large-scale applications. In the present work, water hyacinth was anaerobically digested at different F/I (1.0, 5.0, 10.0, and 30.0), mesophilic temperatures (30 and 40 °C), and supplementation settings using non-acclimatized and acclimatized inoculum to determine the process’s optimal conditions through kinetics (modified Gompertz, Chen and Hashimoto, and first-order) and energy analyses. The F/I ratio had a directly proportional effect on the methane yield [N mL·CH4/g·VS], which ranged from 416.8 ± 6.2 (F/I = 1.0) to 263.8 ± 26.9 (F/I = 30.0). The methane production rate [N mL·CH4/g·VS·day] was highest at 40 °C (9.0 ± 0.8) and lowest at F/I = 30 (5.6 ± 2.8). The biomethanation of water hyacinth followed the modified Gompertz and Chen and Hashimoto models when using the non-acclimatized and acclimatized inoculum, respectively. A 30-day pseudo-lag phase was observed at the highest F/I (30) and low temperature (30 °C) but was negligible at higher temperature (40 °C). For a 5.0 m³ biodigester, the highest estimated net energy occurred at F/I = 30 (370.5 ± 22.6 MJ). The doubling times at 40 °C (16.9 ± 0.3 days) were lower than that at 30 °C (49.6 ± 2.5 days). The anaerobic digestion of water hyacinth in batch mode was optimal at higher F/I ratio and high mesophilic temperatures.