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 3kDa molecular weight cut-off results in significant losses of lignosulphonates (26-50%) in the permeate stream, while nanofiltration using membrane with 500Da 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 (27.5g/L) and productivity (0.4g/L/h) by both strains. When permeates from nanofiltrated SSL were used, the strain B. succiniciproducens showed the highest succinic acid concentration (33.8g/L), yield (0.58g per g of consumed sugars) and productivity (0.48g/L/h). The nanofiltration of 1t of thick spent sulphite liquor could lead to the production of 306.3kg of lignosulphonates and 52.7kg of succinic acid, whereas the ultrafiltration of 1t of thick spent sulphite liquor using a 3kDa membrane could result in the production of 237kg of lignosulphonates and 71.8kg of succinic acid when B. succiniproducens is used in both cases.