Efficiency of hydrothermal pretreatment on the anaerobic digestion of pelagic Sargassum for biogas and fertiliser recovery

Abstract

Pelagic Sargassum inundation of coastlines across the North Atlantic Ocean is an ongoing challenge which poses a great threat to economic productivity. This novel study evaluated the valorisation of these invasive seaweeds into biogas and fertiliser using hydrothermal pretreatment and anaerobic digestion technologies. Increasing the severity factor of hydrothermal pretreatment from 1.59 to 3.83 promoted the degradation of organic particulates in Sargassum, resulting in a maximum soluble chemical oxygen demand yield of 27,250 ± 75 mg/L or 237% greater than the unpretreated biomass. However, no linear relationship exists between increased solubilisation and biogas productivity. Peak methane recovery of 116.72 ± 2.14 mL/gVS was achieved at severity factor 2.65 with the decrease thereafter attributed to the formation of Maillard reaction products and inhibitory compounds during hydrothermal pretreatment. The hydrogen sulfide content in the biogas generated also diminished from 3% to 1%. Additionally, the digestate of biogas production is pathogen-free, nutrient-rich and exhibits bio-fertiliser potential.