No abstract

No abstract

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.

Succinic acid production from the monosaccharides xylose, arabinose, glucose, mannose and galactose was studied using the bacterium Actinobacillus succinogenes. In Duran bottle cultures, containing 10 g/L of each of sugar, succinic acid was produced from all sugars except for galactose. The highest succinate yield, 0.56 g/g, was obtained with glucose, whereas the succinate yield was 0.42, 0.38 and 0.44 g/g for xylose, mannose and arabinose, respectively. The specific succinate productivity was 0.7 g/g h for glucose, but below 0.2 g/g h for the other sugars. Batch bioreactor fermentations were carried out using a sugar mixture of the five sugars giving a total concentration of 50 g/L, mimicking the distribution of sugars in spent sulfite liquor (SSL) from Eucalyptus which is rich in xylose. In this mixture, an almost complete conversion of all sugars (except galactose) was achieved resulting in a final succinate concentration of 21.8-26.8 g/L and a total yield of 0.59-0.68 g/g. There was evidence of co-consumption of glucose and xylose, whereas mannose was consumed after glucose. The main by-products were acetate 0.14-0.20 g/g and formate 0.08-0.13 g/g. NADH balance calculations suggested that NADH required for succinate production was not met solely from formate and acetate production, but other means of NADH production was necessary. Results from mixed sugar fermentations were verified using SSL as substrate resulting in a succinate yield of 0.60 g/g. In addition, it was found that CO2 sparging could replace carbonate supply in the form of MgCO3 without affecting the succinate yield.