Restructuring the Conventional Sugar Beet Industry into a Novel Biorefinery: Fractionation and Bioconversion of Sugar Beet Pulp into Succinic Acid and Value-Added Coproducts

Sustainable chemical production should rely on the valorization of crude renewable resources. Waste biomass refining complies with bioeconomy and circular economy initiatives. In this regard, sugar beet pulp (SBP) was efficiently fractionated into pectins, phenolic compounds, and a sugar-rich hydrolysate that was subsequently used as fermentation feedstock for succinic acid production. Phenolic compounds were separated via acidified aqueous ethanol extraction, while pectins were obtained via sequential treatment with HCl, NH3·H2O and ethanol. Hydrolysis of cellulose and hemicellulose was optimized in laboratory and pilot scales leading to 45 g/L of total sugars with glucose and arabinose being the predominant ones. Laboratory-scale fed-batch fermentations were carried out with the bacterial strain Actinobacillus succinogenes cultivated on SBP hydrolysate resulting in the production of 30 g/L of succinic acid concentration with productivity of 0.62 g/L/h and yield of 0.8 g/g. Similar fermentation efficiency was also demonstrated in 50 L bioreactor cultures. Succinic acid crystals were purified from the fermentation broth by two alternative downstream separation processes on the basis of either semipilot scale bipolar membrane electrodialysis with product purity and yield of 79% and 21.2% or acidification of succinate salts using cation exchange resins with product purity and yield of 95% and 80.1%, respectively. The novel biorefinery concept led to 78.6 g of phenolic-rich extract, 303.1 g of a pectin-rich isolate, 268 g of succinic acid, and 208.4 g of remaining solids with 20% protein content from 1 kg of SBP.