Co-production of Monosaccharides and Hydrochar from Green Macroalgae Ulva (Chlorophyta) sp. with Subcritical Hydrolysis and Carbonization

Subcritical water hydrolysis and carbonization of the biomass are an emerging green technology for seaweed biomass processing. In this work, a novel approach for co-generation of two energy streams from seaweed biomass (fermentable sugars and solid hydrochar) with subcritical water from a green macroalgae Ulva sp. was developed. It was found that for the released of glucose, xylose, rhamnose, fructose, and galactose, the process temperature is the most significant parameter, followed by salinity, solid load, and treatment time. For the formation of fermentation inhibitor 5-hydroxymethylfurfural (5-HMF), temperature also was the most important parameter, followed by residence time, salinity, and solid load. The optimum parameters for maximal release of total sugars under minimum formation of 5-HMF were 170 °C (800 kPa abs.), 5% solid loading, 40 min residence time, and 100% salinity. The hydrochar yield was 19.4% and hydrochar high heating value was 20.2 ± 1.31 MJ kg⁻¹. These results provide new detailed information on the subcritical hydrolysis and carbonization of Ulva sp. biomass and show co-production of fermentable monosaccharides and hydrochar. [Figure not available: see fulltext.].