Three membrane-assisted technologies - electrodialysis, nanofiltration, and Donnan dialysis - were investigated with the objective of developing a green and sustainable integrated downstream process for the recovery of biologically produced succinic acid from carob pod-based fermentation broths. For electrodialysis, heterogeneous and homogenous anion-exchange membranes (including such with monovalent-anion-permselective transport properties) were tested with synthetic model solutions in order to select the most suitable membrane. For nanofiltration, six polymeric membranes were tested to filter the obtained electrodialysis concentrates, and according to the results obtained, three of them (NF270, NF-DK and NF-DL) were selected for further experiments. The performance of these membranes was compared in a diafiltration operation mode with model carboxylates solutions and with simulated fermentation broths, all showing rejections above 90% for succinate and reaching negative rejections for acetate and formate. However, reduced fluxes and fouling were observed in the experiment with simulated fermentation broth containing a carob pod extract. Therefore this medium was treated by electrodialysis, producing a concentrate rich in ionic species, including succinate, but leaving behind the non-ionic and high-molecular mass species. This concentrate was treated by nanofiltration, thus achieving an almost complete removal of accompanying formate and acetate species. Finally, Donnan dialysis was employed to replace the metallic cations in the succinate salts in the nanofiltration retentate by H+. The results showed approximately 76% of cations removal, which was traduced in the same percentage of obtained free succinic acid. Thus, the proposed integrated membrane-assisted process represents a promising new alternative to the existing downstream technologies for bio-based succinic acid recovery.
- Donnan dialysis
- Succinic acid