Comparison of the Electrodialysis Performance in Tartrate Stabilization of a Red Wine Using Aliphatic and Aromatic Commercial and Modified Ion-Exchange Membranes

Identification of Fouling Occurring during Coupled Electrodialysis and Bipolar Membrane Electrodialysis Treatment for Tofu Whey Protein Recovery

Tofu whey, a by-product of tofu production, is rich in nutrients such as proteins, minerals, fats, sugars and polyphenols. In a previous work, protein recovery from tofu whey was studied by using a coupled environmental process of ED + EDBM to valorize this by-product. This process allowed protein recovery by reducing the ionic strength of tofu whey during the ED process and acidifying the proteins to their isoelectric point during EDBM. However, membrane fouling was not investigated. The current study focuses on the fouling of membranes at each step of this ED and EDBM process. Despite a reduction in the membrane conductivities and some changes in the mineral composition of the membranes, no scaling was evident after three runs of the process with the same membranes. However, it appeared that the main fouling was due to the presence of isoflavones, the main polyphenols in tofu whey. Indeed, a higher concentration was observed on the AEMs, giving them a yellow coloration, while small amounts were found in the CEMs, and there were no traces on the BPMs. The glycosylated forms of isoflavones were present in higher concentrations than the aglycone forms, probably due to their high amounts of hydroxyl groups, which can interact with the membrane matrices. In addition, the higher concentration of isoflavones on the AEMs seems to be due to a combination of electrostatic interactions, hydrogen bonding, and π-π stacking, whereas only π-π stacking and hydrogen bonds were possible with the CEMs. To the best of our knowledge, this is the first study to investigate the potential fouling of BPMs by polyphenols, report the fouling of IEMs by isoflavones and propose potential interactions.

Phosphates Transfer in Pristine and Modified CJMA-2 Membrane during Electrodialysis Processing of NaxH(3-x)PO4 Solutions with pH from 4.5 to 9.9

Phosphate recovery from different second streams using electrodialysis (ED) is a promising step to a nutrients circular economy. However, the relatively low ED performance hinders the widespread adoption of this environmentally sound method. The formation of "bonded species" between phosphates and the weakly basic fixed groups (primary and secondary amines) of the anion exchange membrane can be the cause of decrease in current efficiency and increase in energy consumption. ED processing of Na_xH_(3-x)PO₄ alkaline solutions and the use of intense current modes promote the formation of a bipolar junction from negatively charged bound species and positively charged fixed groups. This phenomenon causes a change in the shape of current-voltage curves, increase in resistance, and an enhancement in proton generation during long-term operation of anion-exchange membrane with weakly basic fixed groups. Shielding of primary and secondary amines with a modifier containing quaternary ammonium bases significantly improves ED performance in the recovery of phosphates from Na_xH_(3-x)PO₄ solution with pH 4.5. Indeed, in the limiting and underlimiting current modes, 40% of phosphates are recovered 1.3 times faster, and energy consumption is reduced by 1.9 times in the case of the modified membrane compared to the pristine one. Studies were performed using a new commercial anion exchange membrane CJMA-2.

How Chemical Nature of Fixed Groups of Anion-Exchange Membranes Affects the Performance of Electrodialysis of Phosphate-Containing Solutions?

Innovative ion exchange membranes have become commercially available in recent years. However, information about their structural and transport characteristics is often extremely insufficient. To address this issue, homogeneous anion exchange membranes with the trade names ASE, CJMA-3 and CJMA-6 have been investigated in Na_xH_(3-x)PO₄ solutions with pH 4.4 ± 0.1, 6.6 and 10.0 ± 0.2, as well as NaCl solutions with pH 5.5 ± 0.1. Using IR spectroscopy and processing the concentration dependences of the electrical conductivity of these membranes in NaCl solutions, it was shown that ASE has a highly cross-linked aromatic matrix and mainly contains quaternary ammonium groups. Other membranes have a less cross-linked aliphatic matrix based on polyvinylidene fluoride (CJMA-3) or polyolefin (CJMA-6) and contain quaternary amines (CJMA-3) or a mixture of strongly basic (quaternary) and weakly basic (secondary) amines (CJMA-6). As expected, in dilute solutions of NaCl, the conductivity of membranes increases with an increase in their ion-exchange capacity: CJMA-6 < CJMA-3 << ASE. Weakly basic amines appear to form bound species with proton-containing phosphoric acid anions. This phenomenon causes a decrease in the electrical conductivity of CJMA-6 membranes compared to other studied membranes in phosphate-containing solutions. In addition, the formation of the neutral and negatively charged bound species suppresses the generation of protons by the "acid dissociation" mechanism. Moreover, when the membrane is operated in overlimiting current modes and/or in alkaline solutions, a bipolar junction is formed at the CJMA- 6/depleted solution interface. The CJMA-6 current-voltage curve becomes similar to the well-known curves for bipolar membranes, and water splitting intensifies in underlimiting and overlimiting modes. As a result, energy consumption for electrodialysis recovery of phosphates from aqueous solutions almost doubles when using the CJMA-6 membrane compared to the CJMA-3 membrane.