Sergey Mikhaylin

Fouling on ion-exchange membranes: Classification, characterization and strategies of prevention and control

The environmentally friendly ion-exchange membrane (IEM) processes find more and more applications in the modern industries in order to demineralize, concentrate and modify products. Moreover, these processes may be applied for the energy conversion and storage. However, the main drawback of the IEM processes is a formation of fouling, which significantly decreases the process efficiency and increases the process cost. The present review is dedicated to the problematic of IEM fouling phenomena. Firstly, the major types of IEM fouling such as colloidal fouling, organic fouling, scaling and biofouling are discussed along with consideration of the main factors affecting fouling formation and development. Secondly, the review of the possible methods of IEM fouling characterization is provided. This section includes the methods of fouling visualization and characterization as well as methods allowing investigations of characteristics of the fouled IEMs. Eventually, the reader will find the conventional and modern strategies of prevention and control of different fouling types.

Hybrid bipolar membrane electrodialysis/ultrafiltration technology assisted by a pulsed electric field for casein production

Electrodialysis with bipolar membranes (EDBM) is an ecofriendly technology providing a wide spectrum of solutions for modern industry. The main advantage of EDBM is the absence of chemicals during the treatment, which makes it very attractive especially in the food and pharmaceutical sectors. The production of casein, the major milk protein, by means of EDBM is a very interesting approach in the sustainable development context due to the high product purity, no waste generation and the absence of hazardous reagents. Casein is widely used as a food additive in order to improve the food nutritional value as well as to create the desirable functional properties. Moreover, casein is a source of bioactive peptides having beneficial effects on human health. However, the major obstacle hampering the industrial application of EDBM for the production of casein with improved quality is precipitation of casein inside the EDBM stack and membrane scaling. Here we propose a hybrid technology comprising an EDBM module coupled with an ultrafiltration (UF) module. Our results show that the use of the UF module prior to EDBM allows complete prevention of casein precipitation inside the EDBM stack which plays a crucial role in the improvement of EDBM efficiency. In addition, we have found that electroacidification may be performed until pH 5.0 instead of the conventional value of 4.6, which allows a substantial decrease in membrane scaling. Finally, application of pulsed electric field mode allows inhibition of scale formation and OH− leakage, which hastens the EDBM process and increases the membrane lifetime.

Electrochemical acidification of Kraft black liquor by electrodialysis with bipolar membrane: ion exchange membrane fouling identification and mechanisms.

Integrated forest biorefinery offers promising pathways to sustainably diversify the revenue of pulp and paper industry. In this context, lignin can be extracted from a residual stream of Kraft pulping process, called black liquor, and subsequently converted into a wide spectrum of bio-based products. Electrochemical acidification of Kraft black liquor by electrodialysis with bipolar membrane results in lignin extraction and caustic soda production. Even though the implementation of this method requires less chemicals than the chemical acidification process, fouling of the ion exchange membranes and especially bipolar membrane impairs its productivity. Membrane thickness and ash content measurements along with scanning electron microscopy (SEM), elemental analysis (EDX) and X-ray photoelectron spectrometry (XPS) analysis were performed to identify the nature and mechanisms of the membrane fouling. The results revealed that the fouling layer mostly consisted of organic components and particularly lignin. Based on our proposed fouling mechanisms, throughout the electrodialysis process the pH of the black liquor gradually decreased and as a result more proton ions were available to trigger protonation reaction of lignin phenolic groups and decrease the lignin solubility. Due to the abundance of the proton ions on the surface of the cation exchange layers of the bipolar membrane, destabilized lignin macro-molecules started to self-aggregate and formed lignin clusters on its surface. Over the time, these lignin clusters covered the entire surface of the bipolar membrane and the spaces between the membranes and, eventually, attached to the surface of the cation exchange membrane.

Milk protein production by a more environmentally sustainable process: bipolar membrane electrodialysis coupled with ultrafiltration

The increased demand for food production to nourish the rapidly growing human population raises serious sustainability issues for the food sector. Indeed, conventional food production lines involve processes having a significant environmental burden. Hence, the present study aims to demonstrate an environmentally sustainable process of food production. The milk protein was chosen as a model food ingredient due to its exceptional role in the human diet. The proposed innovative process of milk protein production includes bipolar membrane electrodialysis coupled with ultrafiltration (EDBM-UF). The crucial problem during the EDBM-UF of milk, such as different types of membrane fouling, was successfully solved. Moreover, the life cycle assessment of the novel EDBM-UF protein production process was carried out and compared to a conventional acid/base process. Additionally, a sensitivity test of electricity supply at different geographical locations of the world was performed since electricity is the main energy source for the EDBM-UF process and it could be derived from different sources (renewable and non-renewable). The assessment results demonstrate that the proposed electromembrane process has significant environmental benefits compared to the conventional process using chemicals independently from the electricity supply mix from all considered geographical locations. Thus, EDBM-UF could become a prospective industrial technology taking into account environmental concerns and promoting the development of healthy human society.

Formation of peptide layers and adsorption mechanisms on a negatively charged cation-exchange membrane

Polypeptide/solid charged surface interactions are omnipresent in the biomedical and biochemical fields. The present study aimed to understand the adsorption mechanisms of a cation-exchange membrane (CEM) by a well-characterized peptide mixture at three different pH values. Results demonstrated that fouling was important at pH 6, twice lower at pH 2 and negligible at pH 10. At pH 6, ALPMHIR and TKIPAVFK sequences firstly established electrostatic interactions with the negative CEM charges (SO3-) through their positive K and R residues (NH3+) creating a first nanolayer. Secondly, peptide/peptide interactions occurred through their respective hydrophobic residues creating a second nanolayer. At pH 2, VLVLDTDYK and IDALNENK sequences interacted only electrostatically and that in a lower proportion since at acidic pH values, most of the CEM charges would be protonated and uncharged (HSO3) and then limit the potential electrostatic interactions. In addition, the sequences of peptides interacting at pH 2 and 6 were different. This was explained by their structure in terms of residue nature and position in the sequence. At pH 10, no fouling was observed due to the lack of positive peptide charges. To the best of our knowledge, it is the first in-depth study concerning the fouling of CEMs by peptides from a complex mixture.

Electrodialysis in Food Processing

Application of electrodialysis (ED) technology in food processing allows attaining several aims such as food demineralization, modification as well as concentration, and fractionation of food ingredients. A small environmental impact and the opportunity to treat waste streams are one of the most important advantages of ED. Moreover, recent studies reported the successful application of ED in the isolation of bioactive components acting against different types of diseases. This article highlights the main ED configurations and their applications in different food sectors as well as the main problems arising during ED processing and their possible solutions.

How electrodialysis configuration influences acid whey deacidification and membrane scaling

With the rising popularity of Greek-style yogurts in the past few years, the production of acid whey has drastically increased. If sweet whey is usually further processed, the acid whey valorization comes with challenges because its drying is jeopardized by its high mineral and organic acid contents. For this reason, prior demineralization and deacidification are usually performed at industrial scale using a combination of ion exchange resins and electrodialysis. This whole process represents large amounts of resources and energy consumption as well as an important production of effluents. The optimization of the electrodialysis technique, currently the focus of a few studies, could result in the replacement of the serial processes and would provide a cost-effective and eco-efficient alternative. In this work, the demineralization and deacidification of acid whey were compared via 2 electrodialysis configurations: one conventional and one using bipolar membranes. Both configurations allowed to reach interesting demineralization (67%) and deacidification (44%) rates. However, even though the appearance of fouling or scaling has never been reported, scalings of different natures were observed on membranes using both configurations. Amorphous calcium phosphate was identified on the anion exchange membranes for both configurations while calcite and brucite were identified on cation exchange ones using the bipolar membrane configuration. These scaling formations were linked to the migration of divalent ions and water splitting phenomenon caused by a high demineralization rate or by an already formed significant scaling.