Enhancing biogas production from caribbean pelagic Sargassum utilising hydrothermal pretreatment and anaerobic co-digestion with food waste

Abstract

The recurring inundation of beaches in the tropical North Atlantic by pelagic Sargassum and the associated social, ecological and economic challenges, have aroused great interest in its potential use as a marine energy crop. However, to date, the seasonal availability and low experimental methane potential of these invasive brown seaweeds have hindered their commercial exploitation as feedstock for sustainable energy production. This novel study evaluated Caribbean pelagic Sargassum and the synergistic interactions of hydrothermal pretreatment and co-digestion with food waste at different mixture ratios, on biogas production enhancement and bio-fertiliser recovery. Batch testing revealed that hydrothermal pretreatment promoted the hydrolysis of organics in pelagic Sargassum and food waste, thus increasing methane recovery from mono-substrate digestion by 212.57% and 10.16%, respectively, in comparison to the untreated samples. Co-digestion of pelagic Sargassum and food waste redistributed metal elements and raised the buffering capacity of the digester, facilitating high organic loadings without pH control. Food waste also provided lipids to the seaweed feed which augmented the digestion performance. The maximum cumulative methane yield of 292.18 ± 8.70 mL/gVS was obtained from a blend of co-pretreated pelagic Sargassum and food waste at the weight ratio 25:75. Screening of the whole digestate from co-digestion indicated bio-fertiliser potential. However, the solid fraction necessitates arsenic remediation to meet international soil standard guidelines. The findings of this study are promising and suggest opportunity for the design, scale up and optimisation of biogas systems, equipped with hydrothermal pretreatment for utilisation of Sargassum seaweeds during influx.