Pretreatment of spent sulphite liquor via ultrafiltration and nanofiltration for bio-based succinic acid production

Ultrafiltration and nanofiltration of spent sulphite liquor (SSL) has been employed to evaluate the simultaneous production of lignosulphonates and bio-based succinic acid using the bacterial strains Actinobacillus succinogenes and Basfia succiniciproducens. Ultrafiltration with membranes of 10, 5 and 3 kDa molecular weight cut-off results in significant losses of lignosulphonates (26-50%) in the permeate stream, while nanofiltration using membrane with 500 Da molecular weight cut-off results in high retention yields of lignosulphonates (95.6%) in the retentate stream. Fed-batch bioreactor cultures using permeates from ultrafiltrated SSL resulted in similar succinic acid concentration (27.5 g/L) and productivity (0.4 g/L/h) by both strains. When permeates from nanofiltrated SSL were used, the strain B. succiniciproducens showed the highest succinic acid concentration (33.8 g/L), yield (0.58 g per g of consumed sugars) and productivity (0.48 g/L/h). The nanofiltration of 1 t of thick spent sulphite liquor could lead to the production of 306.3 kg of lignosulphonates and 52.7 kg of succinic acid, whereas the ultrafiltration of 1 t of thick spent sulphite liquor using a 3 kDa membrane could result in the production of 237 kg of lignosulphonates and 71.8 kg of succinic acid when B. succiniproducens is used in both cases.