UV-detoxification of spent sulfite liquor for polymerization of lignosulfonates and succinic acid fermentation with Actinobacillus succinogenes

Abstract

Spent Sulfite Liquor (SSL), a byproduct of sulfite pulp production, contains lignosulfonates (LS) dissolved in a liquid phase rich in sugars, and phenolic substances. This study investigates the effects of UV-irradiation on SSL as a microbial substrate. UV-irradiation of SSL resulted in the polymerization of LS. The molecular weight of LS increased from 1949 Da to 5637 Da (at 3 days of irradiation). FTIR spectroscopy revealed structural changes, including an increase in phenolic OH groups and the formation of β-O-4 ether linkages. Batch fermentations with Actinobacillus succinogenes demonstrated that UV-irradiated SSL led to higher succinic acid production and reduced by-product formation. By product formation was reduced from 0.90 g byproduct per g succinic acid to only 0.62 g in irradiated media. Although the initial lag phase was longer for irradiated SSL, acid production eventually exceeded that of non-irradiated SSL and standard medium. Ultimately, a concentration of 14.40 g L-1 with a yield of 0.56 g of succinic acid per gram of consumed sugar was attained. This represented an increase of 3.01 g L-1 compared to standard media. In conclusion, UV-irradiation upgraded SSL by a higher specificity of succinic acid and allowing better utilization of LS in various applications through polymerization, aligning with sustainable production goals.