Effects of anaerobic digestion pretreatment on the pyrolysis of Sargassum: Investigation by TG-FTIR and Py-GC/MS

•Anaerobic digestion provides an alternative pretreatment for pyrolysis process.•The Sargassum structure was loosened due to the use of biodegradable fractions.•Mild anaerobic digestion pretreatment facilitated the release of gaseous product.•The relative content of N-compounds and hydrocarbons was enhanced with pretreatment.