Valorization of spent sulphite liquor for succinic acid production via continuous fermentation system

Spent sulphite liquor has been evaluated in continuous cultures for succinic acid production using Actinobacillus succinogenes and Basfia succiniciproducens. Continuous cultures were initially carried out at constant dilution rate (0.04 h−1) and varying commercial xylose concentrations (23-55 g/L) or constant xylose concentration (40 g/L) and varying dilution rates (0.02-0.25 h−1) showing that dilution rates of 0.02-0.15 h−1 led to satisfactory succinic acid production by both strains. In continuous cultures using nanofiltrated spent sulphite liquor, the highest yields were achieved at dilution rate of 0.02 h−1 (0.48 g/g for A. succinogenes and 0.55 g/g for B. succiniciproducens), while the highest productivities were obtained at dilution rates of 0.04 h−1 for A. succinogenes cultures (0.67 g/L/h) and 0.1 h−1 for B. succiniciproducens cultures (1.6 g/L/h). Metabolic flux analysis demonstrated higher biomass concentrations in A. succinogenes cultures carried out in both xylose and nanofiltrated spent sulphite liquor, while B. succiniproducens cultures were more robust regarding succinic acid production efficiency in either xylose or nanofiltrated spent sulphite liquor.