Production of ethanol, butanol, itaconic acid, 3-hydroxypropionic acid, polyhydroxyalkanoates, and lignin from lignocellulosic biomass

Abstract

The conversion of lignocellulosic biomass into biofuels, platform chemicals, and bioplastics offers a sustainable pathway for supply chain management. It reduces dependence on fossil resources and supports the development of a circular economy. To minimize water and chemical consumption during pretreatment, we proposed a one-pot CaO pretreatment method applied to corn stover (CS) and brewer's spent grain (BSG). This was followed by pH adjustment using either H₃PO₄ (P) or H₂SO₄ (S) and subsequent enzymatic hydrolysis. The hydrolysates (CS-P, CS-S, BSG-P, and BSG-S) were directly used for producing ethanol with Saccharomyces cerevisiae, n-butanol with Clostridium tyrobutyricum, 3-hydroxypropionic acid (3-HP) with Issatchenkia orientalis, itaconic acid (IA) with Aspergillus terreus, and polyhydroxyalkanoates (PHA) with Haloferax mediterranei. The results showed that the fermentation performance of the resulting hydrolysates is closely linked to the type of acid used for pH adjustment and the source of biomass. BSG hydrolysates outperformed CS in butanol (6.7 g L⁻¹), IA (8.0 g L⁻¹), and 3-HP (10.6 g L⁻¹) production, due to BSG's higher nitrogen content and more favorable C/N ratio, which supported microbial growth and acid biosynthesis. Conversely, CS hydrolysates excelled in ethanol (23 g L⁻¹ for CS-P) and PHA (0.27 g g⁻¹ substrate for CS-P) production, attributed to their higher sugar concentration. Moreover, the lignin-rich hydrolysis residues from CS and BSG had >90% and 80% SGH-type lignin, respectively. Interestingly, BSG lignins displayed substantially low M_w (551–841 g mol⁻¹ vs. 4999–5142 g mol⁻¹) and Đ_M (1.5–2.0 vs. 8.0–8.3) compared to CS lignins. This work demonstrates the feasibility of using one-pot CaO pretreatment to directly produce various value-added products through precision fermentation, thereby advancing a circular bioeconomy.