Biomass to bioproducts by integrated biorefinery strategy: ultrasonic pretreatment, dark fermentation and enzyme hydrolysis

Abstract

The utilization of technology promoting energy indispensable to biorefinery applications drives the need for efficient biomass valorization strategies. This study investigates an integrated approach combining ultrasound pretreatment (US), dark fermentation, and enzyme hydrolysis (EH) to maximize the production of biohydrogen (H ), volatile fatty acids (VFA), total reducing sugars (TRS), and total proteins (PR) from lignocellulosic biomasses. Four feedstocks were examined: orange peel (OP), sugar beet pulp (SBP), brewers spent grain (BSG), and rice husk (RH). Ultrasound pretreatment at 120 min, 45 ◦ C, and 100 % of amplitude significantly enhanced the organic matter solubilization across all substrates, with OP exhibiting the highest solubilized organic matter (54.7 g O 2 /L; 25 g C/L, 21 g TRS/L and 8.7 g PR/L) with specific energy (Es) of 6.13 MJ/kg. During the dark fermentation process, the highest H 2 dry matter, while BSG and SBP, generate 17.9 mL H 2 production was obtained with OP, yielding 20.8 mL H /g dry matter, and 14.6 mL H 2 2 /g /g dry matter, respectively. Subsequently, VFAs production exhibited maximum yield with OP (5.37 g H-Ac/L), SBP (4.61 g H-Ac/L), and BSG (4.33 g H-Ac/L). Subsequent enzyme hydrolysis of the pretreated solid fractions further increased TRS concentrations, reaching 32.5 g/L for OP, 29.0 g/L for BSG, and 27.0 g/L for SBP. RH consistently exhibited the lowest yields across all bioproducts, attributed to its high lignin content and low enzymatic accessibility. Overall, OP proved to be the most promising substrate for integrated bioproduct recovery, demonstrating the efficiency of this biorefinery approach for lignocellulosic waste valorization.