Background and Summary

BACKGROUND OF THE INVENTION

A. Field of the Invention

The present invention relates generally to separation and purification of ion mixtures in aqueous solutions, that at least in part contains water, and, more particularly, to a system and method for selective fractionation of ions with different charge (at any pH value) and/or size and the use of such for enrichment of ions, particular valuable ions, from industrial streams by novel electrodialysis, hereinafter Selectrodialysis.

Several documents are cited throughout the text of this specification. Each of the documents herein (including any manufacturer's specifications, instructions etc.) is hereby incorporated by reference; however, there is no admission that any document cited is indeed prior art of the present invention.

B. Description of the Related Art

Separation of ions from aqueous solution can be achieved in various ways, including ion exchange, precipitation, reverse osmosis, electrodialysis, and nanofiltration. With these methods, however, only a limited effect of fractionation can be obtained, except for those cases where a specific chemical reaction can be exploited based on precipitation or complexation. A general method for complete fractionation of ions from an aqueous solution does not exist. Present invention provides such complete fractioning or at least to a level of about 90% or more of an original ion concentration, preferably to a level of about 95% or more of an original ion concentration, yet more preferably to a level of about 98% or more of an original ion concentration and most preferably to a level of about 99% or more of an original ion concentration. Ion exchange is based on the exchange of an anion, present on an anion exchanging resin, with an anion in the solution, or the exchange of a cation, present on a cation exchanging resin, with a cation in the solution. The resins have a limited selectivity, which cannot be used for fractionation of different anions or fractionation of different cations. In some cases, the charge of a cation or anion can be reversed by changing the pH (depending on the speciation profile of the cation or anion), or by the addition of a complexing agent. However, these methods are not applicable in general. Similarly, some precipitation reactions can be exploited, such as the precipitation reaction of CaC0 ₃ upon the addition of Ca(OH) ₂ , NaOH or Na ₂ C0 ₃ . Again, this method is not generally applicable.

Reverse osmosis is a membrane separation technique in which ions are retained by a membrane, allowing the solvent (in most cases water) to permeate through the membrane. Multivalent ions are somewhat better retained than monovalent ions (both with positive and negative charge), but this effect is only noticeable through the fragment of ions leaking through the membrane, leaving the solvent essentially free of dissolved ions. Similarly, nanofiltration membranes retain both monovalent and multivalent ions to some extent, although differentiation is more effective here. A majority of monovalent ions may permeate, whereas a majority of multivalent ions may be rejected. However, a complete separation is not possible. Electrodialysis is a membrane separation method with an electric potential as the driving force. Membranes have ion exchange capabilities and can be of the anion exchange type or the cation exchange type. Various anion exchange type and cation exchange type membranes are available in the art as for instance described in US7544278 on "Ion exchange membranes, methods and processes". In general, these membranes do not differentiate between different ions, although some differences in transport rate through the membranes can be observed. These differences, however, do not lead to fractionation. Some membranes claim to be selective for monovalent (an)ions compared to multivalent (an)ions. The fractionation effect that can be obtained in this way, however, is limited and similar to the effect that can be obtained with nanofiltration.

Thus, there is a need in the art for more accurate fractionation of ions from an aqueous solution. Present invention solves this problem by a new technology based on a novel electrodialysis system and electrodialysis apparatus. This solves the long-standing industrial problem of developing a highly selective separation of ions with a difference in charge. selected ion in an aqueous separator solution that at is input foreseen to receive an aqueous fluid, which contains salt in desired concentration.

Another aspect of the invention is that the first compartment or the compartment that is at least in part formed by a CM and AM membrane, is at its input foreseen with a means to receive an ion mixture aqueous feed solution; and that the second compartment is at least in part formed by a MVA and AM membrane, is at its input foreseen with a means to receive an aqueous fluid, which contains salt in desired concentration; and that the third compartment is at least in part formed by a AM and CM membrane, is at its input foreseen with a means to receive an aqueous fluid, which contains and receives salt as a brine; and the forth compartment or the compartment that is at least in part formed by a CM and AM membrane, is at its input foreseen with a means to receive an ion mixture aqueous feed solution; and that the fifth compartment is at least in part formed by a MVA and AM membrane, is at its input foreseen with a means to receive an aqueous fluid, which contains salt in desired concentration.

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

Detailed Description

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Before the invention is described in detail, it is to be understood that this invention is not limited to the particular component parts of the devices described or process steps of the methods described as such devices and methods may vary. It is also to be understood that the terminology used herein is for purposes of describing particular embodiments only, and is not intended to be limiting. It must be noted that, as used in the specification and the appended

5 This technology is useful to separate monovalent and multivalent ions with a selectivity superior to currently available techniques such as nanofiltration or conventional electrodialysis using selective membranes.

SUMMARY OF THE INVENTION

Present invention solves the long-standing industrial problem of highly selective separation of ions with a difference in charge. Moreover the present invention allows to separate monovalent and multivalent ions with a superior selectivity as compared to currently available techniques such as nanofiltration or conventional electrodialysis using selective membranes.

The present invention makes use of a new process configuration based on the electrodialysis process, as shown in the figure 3 below. Electrodialysis makes use of two compartments (denoted as the diluate and the concentrate) or series thereof, whereas in the new invention, three compartments of different functionality are used. In this figure, CM is a regular cation exchanging membrane; AM is a standard anion exchanging membrane, and MVA is an anion exchanging membrane with a limited selectivity for monovalent anions, as described before. Due to a careful choice of the relative volumes in the different compartments, a complete removal of monovalent ions from multivalent ions is obtained in the concentrate compartment for any aqueous feed solution. In the absence of multivalent anions, selective removal of a monovalent anion from another monovalent anion can be achieved.

In accordance with the purpose of the invention, as embodied and broadly described herein, the invention is broadly drawn to a system electrodialysis that uses a particular sequence of a regular cation exchanging membrane, a standard anion exchanging membrane, and an anion exchanging membrane under an electric field that form flow through compartments.

The present invention solves the problems of the related art of accurate fractionation of ions from an aqueous solution by an ion-selective electrodialysis apparatus, which apparatus comprises at least two unit comprising flow trough compartments which unit is least in part are formed by a sequence or stack of membranes comprising at least two cation exchanging membrane (CM), at least two non-selective anion exchanging membrane (AM) and at least two anion selective membrane (MVA) and a whereby the apparatus further comprises an electric field generating means or electrical potential generating means, characterized in that

3 the compartments of the units are at least in part formed by two CM membrane and two MVA membrane and two inner separating AM membrane dividing into five compartments, whereby the first compartment that is at least in part formed by an AM membrane and a CM membrane (feed compartment), the second compartment is at least in part formed by a MVA membrane and an AM membrane (selector compartment), the third compartment is at least in part formed by a CM membrane and a MVA membrane (brine compartment), the forth compartment that is at least in part formed by an AM membrane and a CM membrane (feed compartment), the fifth compartment is at least in part formed by a MVA membrane and an AM membrane (selector compartment).

In one aspect of the invention, of the electric field generating means the ion-selective electrodialysis apparatus described here above comprises at least one electrode on either side of a stack or sequence of membranes Another aspect of the invention the selectivity of the MVA membrane for cations, anions and/or divalent anions in a salt mixture is adjustable.

Another aspect of the invention the ion-selective electrodialysis apparatus, whereby the AM and/or MVA membranes can be replaced by other selective membrane(s) with specific selective characteristics.

Another aspect of the invention the configuration of the ion-selective electrodialysis apparatus, which apparatus can separate ions under neutral condition and the pH keeps neutral constant during operation.

Another aspect of the invention the configuration of the ion-selective electrodialysis apparatus, which apparatus can also separate ions under acidic or basic conditions.

In still another aspect of the invention, each compartment of the at least one unit has an input and an output.

In specific embodiments the second inner compartment or the compartment that at least in part is formed by an AM and a MVA membrane is a selector compartment to isolate a

4 claims, the singular forms "a," "an" and "the" include singular and/or plural referents unless the context clearly dictates otherwise.

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

Definitions

In this application the "selector" is on the meaning of the space, zone, confined environment or compartment between an AM and MVA membrane, whereby such space, zone, confined environment or compartment receives a watery fluid from said as input and deliveres a mixture of concentrated or separated ions at its output.

The following detailed description of the invention refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. Also, the following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims and equivalents thereof.

Separation of ions from aqueous solution can be achieved in various ways, including ion exchange, precipitation, reverse osmosis, electrodialysis, and nanofiltration. With these methods, however, only a limited effect of fractionation can be obtained, except for those cases where a specific chemical reaction can be exploited based on precipitation or complexation. A general method for enhanced fractionation of ions from an aqueous solution based on mere charge differences does not exist. Ion exchange is based on the exchange of an anion, present on an anion exchanging resin, with an anion in the solution, or the exchange of a cation, present on a cation exchanging resin, with a cation in the solution. The resins have a limited selectivity, which cannot be used for fractionation of different anions or fractionation of different cations. In some cases, the charge of a cation or anion can be reversed by changing the pH (depending on the speciation profile of the cation or anion), or by the addition of a complexing agent. However, these methods are not applicable in general.

Similarly, some precipitation reactions can be exploited, such as the precipitation reaction of CaC0 ₃ upon the addition of Ca(OH) ₂ , NaOH or Na ₂ C0 ₃ . Again, this method is not generally applicable.

Reverse osmosis is a membrane separation technique in which ions are retained by a membrane, allowing the solvent (in most cases water) to permeate through the membrane. Multivalent ions are somewhat better retained than monovalent ions (both with positive and negative charge), but this effect is only noticeable through the fragment of ions leaking through the membrane, leaving the solvent essentially free of dissolved ions.

Similarly, nanofiltration membranes retain both monovalent and multivalent ions to some extent, although differentiation is more effective here. A majority of monovalent ions may permeate, whereas a majority of multivalent ions may be rejected. However, a complete separation is not possible.

Electrodialysis is a membrane separation method with an electric potential as the driving force. Membranes have ion exchange capabilities and can be of the anion exchange type or the cation exchange type. In general, these membranes do not differentiate between different ions, although some differences in transport rate through the membranes can be observed. These differences, however, do not lead to fractionation. Some membranes claim to be selective for monovalent (an)ions compared to multivalent (an)ions. The fractionation effect that can be obtained in this way, however, is limited and similar to the effect that can be obtained with nanofiltration, as was proven by the applicants [Van der Br ggen, B.; Koninckx, A.; Vandecasteele, C. Separation of monovalent and divalent ions from aqueous solution by electrodialysis and nanofiltration. Water Res. 2004, 38 (5), 1347-1353]. Referring now specifically to the drawings, the novel electrodialysis system of present invention (Selectrodialysis) according to an embodiment of the present invention is illustrated in Figure 1. According to the principle shown in figure 1 the feed comprises a salt mixture with cation A , monovalent anion B ^" and divalent anion C ^" .. The proposed product is an enriched C ^2" solution. By applying an electrical potential over the electrodes on either side of a stack of membranes, anions are attracted to the anode whereas cations are attracted to the cathode. In contrast to conventional electrodialysis, the membrane stack is different for electrolyse system and apparatus, Selectrodialysis, of present invention and comprises a sequence of a cation exchanging membrane (CM), a non-selective anion exchanging membrane (AM) and an anion selective membrane (MVA). Cations are transported through the CM membrane, while anions (regardless of their charge) are transported through AM. In present invention a compartment formed by an AM and a MVA membrane, herein after also denoted as the 'selector' compartment, can contain an increased concentration of multivalent anions. More B ^" will penetrate through the monovalent selective MVA membrane than C ^" (m>n).

In the selector, cation A cannot penetrate through the AM membrane due to Donnan exclusion and hence retained in the stream. Thus, the transport of the anions B ^" and C ^" to the following compartment will be determined by two rules:

1) Electro-neutralization: as no cation can migrate through the anion exchange membranes, the amount of the total charge equivalence (T ) of the outgoing anions from the selector through the monovalent selective anion exchange membrane (MVA) should be the same as the amount of the T of the incoming anions, i.e., T _eq = 3m mol eq.

2) Membrane selectivity: as the MVA membrane is a monovalent selective membrane, more B ^" will penetrate through the MVA membrane than C ^2" . Suppose the MVA membrane selectivity to the divalent anion C ^" towards monovalent anion B ^" is ξ ( ξ < 1 ), which is normally regarded as a constant ( _cons ).

2 _t

Based on those two rules mentioned above, suppose n molar of C ^" is transported through the MVA membrane, thus m-n molar of C ^" is retained in the selector; and m+2(m-n) molar of B ^" is transported through the MVA membrane, as shown in Figure 1. Therefore, the membrane n

selectivity for C ^" towards B ^" is ξ _εοη5 = P _B =

m + 2(m - ri)

Thus, for a salt mixture in the selector, containing initially x moles A , y moles B ^" and (x-y)/2 moles C suppose the salt mixture volume V. After a period t, the concentration of the anion (x - )/2 ^~ —— + (m -n)

C ^2' increases from c _c (0) = — to c _c (t) =— -—— ; and the concentration of

V y— 2(m " n)

anion B ^" from c _s (0) =— decreases to c _B (t) = — . After a period t', the y— 2(m -ή) ·—

concentration of B ^" decreases to c _B (t') = — and the concentration of C ^2"

(x -y) , t

1 t

increases to c _c (t ') =— — — . Therefore, the concentration of anion B ^" decreases and the concentration of anion C ^" increases as a function of time, until the concentration of anion B ^" in the selector gets depleted.

This selectivity can be adjusted according to the needs of the application by a careful choice of process conditions, such as charge density, relative volume of feed and both concentrate compartments, and hydraulic conditions. Naturally, the membrane itself plays a central role as well.

The electrodialysis stack of present invention, Selectrodialysis stack, can be used to separate, fractionate and enrich anions, negatively charged organic ions or small negatively charged proteins, if the proper, nonselective and selective membranes are installed. The method can be used to separate, fractionate and enrich cations, positively charged organic ions or small positively charged proteins, since the membranes can be replaced by the proper nonselective and selective membranes with adapted characteristics of ion transport. The electrodialysis stack of present invention (Selectrodialysis) can be used to separate, fractionate and enrich cations, organic ions or small charged proteins, if the proper nonselective and selective membranes can be installed. The membrane selectivity can be due to size exclusion, charge repulsion, hydrophilicity difference, or other characteristics between membranes and the ions.

The separation efficiency depends on membrane characteristics (the selectivity to the target ion), operation parameters (time, applied current/voltage, flow rate, spacers, pH etc.) and the stack configuration. The product concentration depends upon the membrane permselectivity to the co-ions (due to electro-neutralization takes an important role), the separation efficiency to the counter-ions, the original product stream concentration, feed concentration, operational time period, applied current/voltage, stack configuration and operation parameters.

EXAMPLES

Example 1: Separation and enrichment of sulphate from sulphate/chloride mixture

Experiments were performed to separate and enrich S0 ₄ ^2" from NaCl/Na ₂ S0 ₄ solution by a single AM-MVA-CM selector. Figure 2 shows the concentration of chloride and the molar ratio between sulfate and chloride in the selector compartment. The results show that the selector can enrich sulfate from a sulfate/chloride solution, the sulfate/chloride ratio rising from 1 to 5.3. Example 2: Separation and enrichment of sulphate and phosphate from Η _Χ ΡΟ 70 ^" /NO3 /SO4 ² ) mixture

Similarly, a fractionation between phosphate and sulphate from monovalent ions in (concentrated) wastewater from the food industry was carried out by using the same Selectrodialysis stack. Concentration changes (%) of the anions are shown in Figure 3 as a function of time. The concentration of phosphate in the product stream (expressed as H _x P04 ^y" ) increased by a factor 2.5, and the concentration of sulfate ion increased to 1.6 times the initial concentration. The concentration of monovalent anions (i.e., CI ^" and N0 ₃ ^" ) decreased to 44% of the initial concentration. It can be expected that more phosphate would be fractionated in the selector if a longer period of operation were performed and that sulphate can be separated from phosphate if an extended AM-MVA-CM selector configuration were applied in the experiment.

Example 3: A multiple AM-MVA-CM selector configuration for ions/charged compounds fractionation

The electrodialysis system of present invention can be organized in a multi-compartment approach (multiple selector configuration). Where there are multiple units; each unit comprising the three compartments of different functionality in particular whereby the three compartments formed by CM (a regular cation exchanging membrane); AM (a standard anion exchanging membrane), and MVA (an anion exchanging membrane with a limited selectivity 5 for monovalent anions). Thus, the AM-MVA-CM selector can be extended to a multiple selector configuration for various industrial applications for ions/charged compounds fractionation, as shown in Figure 5. Example 4: Production of amino acids and fatty acids

A particular embodiment of present invention is the use of the electrodialysis system of present invention for the production of amino acids and fatty organic acids. Conventionally, pH adjustment to the iso-electrical point of an organic acid is used to separate it from a mixture of acids [Huang, C. et al. Application of electrodialysis to the production of organic acids: State of the art and recent developments, J. Membr. Sci. 2007, 288 (1-2), 1—12]. Moreover, organic acids with similar pKa value are difficult to be fractionated by pH adjustment. By using Selectrodialysis, pH adjustment is not necessary. Moreover, organic acids with similar pKa values can possibly be fractionated. Separating of taurine, glycine and arginine from inorganic salts in scallop broth is a practical example shown in the literature to be cumbersome [Atungulu, G. et al. Ion exchange membrane mediated electrodialysis of scallop broth Ion, free amino acid and heavy metal profiles, J. Food Eng. 2007, 78 (4), 1285- 1290], to which Selectrodialysis is applied.

Based on the properties of selectrodialysis, there has a high potential to apply it for amino acids and fatty acids purification. Amino acids and fatty acids are widely used in food and pharmaceutical industries; however, some of the organic acids are difficult to obtain. For example, fatty acids can be obtained from fermentation broths, which has already be reported by various literatures, but it is difficult to separate the target fatty acids from the fermentation broths with complex components; and the separation and purification processes are always costly and not environmental friendly. By using selectrodialysis, the process could be simplified, fewer chemicals will be added and the by-products can be reduced.

Another example is amino acids: by optimization of current density and pH, small and larger amino acids can be successfully separated from protein hydrolysates by ion-exchange membranes in conventional electrodialysis. However, conventional electrodialysis can only be used for demineralization; the separated neutral amino acids molecules have to be further enriched. The Selectrodialysis configuration can be used for both demineralization (in the feed compartment) and for enrichment (in the product compartment). In those cases mentioned upon, electrodialysis with bipolar membranes (EDBM) can also be applied in organic acids production. EDBM is not a competitor but a partner of selectrodialysis since EDBM has the requirement for low hardness and a high concentration of the target organic salt in the feed, thus, selectrodialysis can be used as the pretreatment of EDBM: remove multivalent ions and enrich the organic ions.

Example 5: Enrichment of chromium (III) from the leather processing industry

Tanning is the main operation in the leather processing. Chromium (III) sulphate is widely used in this process. Due to the toxicity of chromium (III) and it may accumulate in plants, animal and human body, thus, recovery and recycling of the spent chromium is the key for environment protection and for economic benefits.

Suitable chromium (III) selective membranes for electrodialysis separation of chromium (III) PEI modified Nafion® 324 membranes. It is reported that the membrane selectivity Na ⁺ :Cr ³⁺ >0.9. Thus, it has a high potential to apply selectrodialysis with PEI modified Nafion® 324 membranes for chromium (III) enrichment. Figure 6 shows the diagram of using selectrodialysis to enrich chromium (III) from the wastewater. Thus, the wastewater can be treated for discharge and chromium (III) can be recycled for the leather processing. Example 6: Enrichment of phosphate from food industry

Yet another particular embodiment of present invention is the use of the Selectrodialysis system of present invention for recovery of valuable ions. A food industry waste stream treated by reverse osmosis (RO) generates a concentrated brine, which contains a high concentration of salts and nutrient ions, i.e., phosphate, above the discharge limit. Given future depletion of phosphate stocks, it is valuable to enrich and recover phosphate for producing fertilizers. It is very difficult to separate phosphate from the other ions, especially from sulfate, by conventional ED. Selectrodialysis is performed to separate and enrich phosphate from the other ions. The principle of this application is shown in Figure 3. Many companies produce phosphate- rich Wastewater and have to fulfil the discharge legislation to keep the total phosphorus (TP) concentration below (typically) 2 ppm [Hafez, A.; Khedr, M.; Gadallah, H. Wastewater treatment and water reuse of food processing industries, part II: Techno-economic study of a membrane separation technique. Desalination 2007, 214 (1-3), 261-272]. The application of Selectrodialysis for reduction of the TP below 2 ppm is thought to have a good potential for valorization: on the one hand, phosphates can be removed in view of discharge; on the other hand, phosphates can be concentrated to produce struvite as phosphorus source. Given future depletion of phosphate stocks, this may be of growing interest to companies [Doyle, J.D.; Parsons, S.A. Struvite formation, control and recovery. Water Res. 2002, 36, 3925-3940.].

In many countries, it has already been required to recover and recycle phosphorus in the industrial field to reduce the potential of eutrophication of the natural water body. In food industry, high concentrations of phosphate can be found in these streams. Hence, a technique named REM-NUT process has been studied to produce struvite. Selectrodialysis can be used as either the pretreatment or the post-treatment of the REM-NUT process. As shown in Figure 4, selectrodialysis can remove the salts from the feed water hence the effluent from the feed compartment (the diluate) can be reused; meanwhile, the product water which contains concentrated phosphate can be used for struvite crystalization; the brine with low phosphate can be discharged or for further treatment. Figure 4 displays the streams for phosphate-rich wastewater treatment in the Selectrodialysis.

A preliminary experiment on Selectrodialysis was done in a lab scale to concentrate phosphate in the product compartment as shown in Figure 7. The feed liquid was a wastewater from a potato digested effluent with the phosphate concentration of around 90 ppm. The initial liquid in the product compartment was pure NaCl solution with the concentration of around 2500 ppm. It can be seen from Figure 7 that the concentration of phosphate was increased from 0 to more than 400 ppm. No pH adjustment was done during the experiment and the pH of the feed, product and brine was constant. The product stream shows a high potential for phosphate recovery (e.g., production of struvite).

Furthermore, a proposed struvite separation-precipitation system which includes a selectrodialysis installation, a reactor-crystalizer and a submerged ultrafiltration unit is shown in Figure 8.

Example 7: Separation and enrichment of isomers

Yet another particular embodiment of present invention is the use of the Selectrodialysis system for separation and enrichment of isomers. In the pharmaceutical, agrochemical and food industry, separation and enrichment of isomers is important to obtain a more "active" product. An example is the pharmaceutical industry, where many medicines are racemic mixtures, in which only one enantiomer has a positive effect. Thus, enriching the "active" form from the other is a main issue. Conventional electrodialysis with selective chiral selective membranes has been studied [Wang J. et al. Preparation of chiral selective membranes for electrodialysis separation of racemic mixture, J. Membr. Sci. 2006, 276 (1-2), 193-198]. However, the selectivity with a single stage ED was not sufficient. Hence, Selectrodialysis with chiral selective membranes can be used to highly improve the separation efficiency on the racemic mixtures. Cation exchanging membrane (CM), a non-selective anion exchanging membrane (AM) and an anion selective membrane (MVA) are available in the art and described in several manuals including Membrane Technology: in the Chemical Industry 2nd ed by: Suzana Pereira Nunes, Klaus- Viktor Peinemann Author: Wiley | July 2006 | ISBN: 3527313167; Handbook of Membrane Separations: Chemical, Pharmaceutical, Food, and Biotechnological Applications Author: Anil K. Pabby, Syed S.H. Rizvi and Handbook of Membrane Separations: Chemical, Pharmaceutical, Food, and Biotechnological Applications CRC | 2008 | ISBN: 0849395496 | Pages: 1184; Synthetic Polymeric Membranes: Characterization by Atomic Force Microscopy It will be apparent to those skilled in the art that various modifications and variations can be made in size of the compartments, type of the cation exchanging membrane (CM), type of the non-selective anion exchanging membrane (AM) and type of the anion selective membrane (MVA), ionic mixture, concerntration of the salts, electric field, amount of three-compartment units (or multiple units) and design of the electrodialysis system and on the use of the electrodialysis system or apparatus of the present invention and in construction of the system and method without departing from the scope or spirit of the invention. Examples of such modifications have been previously provided.

Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.

Example 8: Purification of tryptophan from corn fermentation broth

Yet the electrodialysis system of this invention (selectrodialysis) can be used to purify tryptophan, which is an essential amino acid for human organisms and an important biomedical precursor. By using selectrodialysis system, more purity can be achieved and less energy will be consumed compare with the conventional purification methods.

The schematic diagram is shown in Figure 9, a standard cation exchange membrane, a "loose" anion exchange membrane and a "tight" anion exchange membrane is used in the basic unit. Two main contents in the broth: tryptophan and acetate are migrating to the selector compartment (forms by a loose anion-exchange membrane and a tight anion-exchange membrane) by the electrical field. Tryptophan, which has higher molecular weight, is retained in the selector by the tight anion exchange membrane; however acetate is permitted to penetrate through the tight membrane due to it has smaller size. Thus, tryptophan can be highly purified by selectrodialysis.

Some embodiments of the invention are set forth below: A first embodiment according to the current invention, concerns an ion-selective electrodialysis apparatus, which apparatus comprises at least two units comprising at least five flow trough compartments which units are least in part are formed by a sequence or stack of membranes comprising at least two cation exchange membranes (CM), at least two standard anion exchange membranes (AM) and at least two anion selective membranes (MVA) and a whereby the apparatus further comprises an electric field generating means or electrical potential generating means, characterised in that:

• the compartments of the units are at least in part formed by two CM membranes and two MVA membranes and two inner separating AM membranes dividing into five compartments, whereby

· the first compartment that is at least in part formed by an AM membrane and a CM membrane (feed compartment, compartment 1)

• the second compartment is at least in part formed by a MVA membrane and an AM membrane (selector compartment, compartment 2)

• the third compartment is at least in part formed by a CM membrane and a MVA membrane (brine compartment, compartment 3)

• the forth compartment that is at least in part formed by an AM membrane and a CM membrane (feed compartment, compartment 4) • the fifth compartment is at least in part formed by a MVA membrane and an AM membrane (selector compartment, compartment 5). We refer for this structure to the graphic display in Figure 10)

As another additional feature, the ion-selective electrodialysis apparatus according to this first embodiment explained above, concerns an apparatus which comprises at least two units comprising six flow trough compartments which unit is least in part are formed by a sequence or stack of membranes comprising at least three cation exchange membranes (CM), at least two non-selective anion exchange membrane (AM) and at least two anion selective membrane (MVA) and a whereby the apparatus further comprises an electric field generating means or electrical potential generating means, characterised in that:

• Compartment 2 or 5, for concentrating or separating a selected ion (selector compartment), of the unit is at least in part formed by an AM membrane wall and at least in part formed by a MVA membrane wall each separating an additional compartment for a CM membrane

• Compartment 1 or 4 that is at least in part formed by an AM membrane and a CM membrane (feed compartment)

• Compartment 3 or 6 is at least in part formed by a MVA membrane and a CM membrane (brine compartment). We refer here for to the graphic display shown in Figure 11.

Yet another second embodiment according to the current invention, concerns an ion-selective electrodialysis apparatus, which apparatus comprises at least two units comprising at least six flow trough compartments which units are least in part are formed by a sequence or stack of membranes comprising at least two cation exchange membrane (CM), at least two nonselective anion exchange membrane (AM) and at least two anion selective membrane (MVA) and a whereby the apparatus further comprises an electric field generating means or electrical potential generating means, whereby:

· Compartment 2 or 5, for concentrating or separating a selected ion (selector compartment), of the unit is at least in part formed by a MVA membrane wall and at least in part formed by an AM membrane wall each separating an additional compartment for a CM membrane

• Compartment 1 or 4 that is at least in part formed by a MVA membrane and a CM membrane (feed compartment)

· Compartment 3 or 6 is at least in part formed by an AM membrane and a CM membrane (brine compartment)

The ion-selective electrodialysis apparatus according to any one embodiment described above including the first and second embodiment, whereby the AM and/or MVA membranes can be replaced by other selective membrane(s) with specific selective characteristics. We refer hereby to Figure 12

A further third embodiment according to the current invention, concerns an ion-selective electrodialysis apparatus, which apparatus comprises at least two units comprising at least five flow trough compartments which units are least in part are formed by a sequence or stack of membranes comprising at least two cation selective membrane (MVC), at least two standard cation exchange membrane (CM) and at least two standard anion exchange membrane (AM) and a whereby the apparatus further comprises an electric field generating means or electrical potential generating means, characterised in that:

· the compartments of the units are at least in part formed by two AM membrane and two MVC membrane and two inner separating CM membrane dividing into five compartments, whereby

• the first compartment that is at least in part formed by an AM membrane and a CM membrane (feed compartment, compartment 1)

• the second compartment is at least in part formed by a CM membrane and a MVC membrane (selector compartment, compartment 2)

• the third compartment is at least in part formed by a MVC membrane and a AM membrane (brine compartment, compartment 3)

• the forth compartment that is at least in part formed by an AM membrane and a CM membrane (feed compartment, compartment 4)

· the fifth compartment is at least in part formed by a CM membrane and a MVC membrane (selector compartment, compartment 5). We refer here for to the graphic display of such structure in Figure 13.

The present invention is also directed to particular ion-selective electrodialysis apparatus according to this third embodiment , which apparatus comprises at least two units comprising six flow trough compartments which unit is least in part are formed by a sequence or stack of membranes comprising at least three cation exchange membranes (CM), at least two nonselective anion exchange membrane (AM) and at least two cation selective membrane (MVC) and a whereby the apparatus further comprises an electric field generating means or electrical potential generating means, characterised in that:

· Compartment 2 or 5 that is at least in part formed by an AM membrane and a CM membrane (feed compartment) • Compartment 3 or 6, for concentrating or separating a selected ion (selector compartment), of the unit is at least in part formed by a CM membrane wall and at least in part formed by a MVC membrane

• Compartment 1 and 4 are the brine compartments. Such structure has been graphically displayed in Figure 14.

A further fourth embodiment according to the current invention, concerns an ion-selective electrodialysis apparatus, which apparatus comprises at least two units comprising at least six flow trough compartments which units are least in part are formed by a sequence or stack of membranes comprising at least two cation exchange membrane (CM), at least two non- selective anion exchange membrane (AM) and at least two cation selective membrane (MVC) and a whereby the apparatus further comprises an electric field generating means or electrical potential generating means, whereby:

• Compartment 2 or 5 that is at least in part formed by an AM membrane and a MVC membrane (feed compartment)

· Compartment 3 or 6, for concentrating or separating a selected ion (selector compartment), of the unit is at least in part formed by a MVC membrane wall and at least in part formed by a CM membrane

• Compartment 1 and 4 are the brine compartments. This has been graphically displayed in Figure 15.

Another aspect of present invention concerns ion-selective electrodialysis apparatus according to any one of the third or fourth embodiments with or without their additional features described here above, whereby the CM and/or MVC membranes can be replaced by other selective membrane(s) with specific selective characteristics.

The present invention is furthermore directed to an ion-selective electrodialysis apparatus which apparatus comprises the multiples of units according to any one of the above described embodiments with or without their additional features described here above. This multiple units each unit comprise three compartments of different functionality. For instance the three compartments formed by CM (a regular cation exchange membrane); AM (a standard anion exchange membrane), and MVA (an anion exchange membrane with a limited selectivity for monovalent anions). Furthermore it is advantageous when such ion-selective electrodialysis apparatus according to any one of the above embodiments comprises recycling means to return the output stream of a certain compartments to upstream compartments. In a specific embodiment this ion-selective electrodialysis apparatus comprises a multiple AM-MVA-CM selector configuration.

A preferred embodiment of the present invention the configuration of the ion-selective electrodialysis apparatus according to any one of the above embodiments (such as the first, second, third or fourth embodiments with or without the above described additional features of present invention), concerns apparatus can separate ions under neutral condition and the pH keeps neutral constant during operation or yet a further preferred embodiment of the present invention the configuration of the ion-selective electrodialysis apparatus according to any one of the above embodiments (such as the first, second, third or fourth embodiments with or without the above described additional features of present invention), concerns apparatus can also separate ions under acidic or basic conditions.

The present invention is also directed to an ion-selective electrodialysis apparatus according to any one of the previous embodiments, whereby the electric field generating means comprises at least one electrode on either side of a stack or sequence of membranes

The present invention is also directed to an ion-selective electrodialysis apparatus according to any one of the previous embodiments, whereby the selectivity of the membranes for cations, anions and/or charged compounds in a salt mixture is adjustable.

According to one embodiment the ion-selective electrodialysis apparatus according to any one of the previous embodiments (such as the first, second, third or fourth embodiments with or without the above described additional features of present invention) comprises membranes which are in tubes from. The ion-selective electrodialysis apparatus according to this embodiment can have the MVA membrane forming an inner tube being surrounded at least in part by a AM membrane tube which is at least in part being surrounded by a CM membrane tube or the ion-selective electrodialysis apparatus according to this embodiment can have the CM membrane forming an inner tube being surrounded at least in part by a AM membrane tube which is at least in part being surrounded by a MVA membrane tube.

According to one embodiment the ion-selective electrodialysis apparatus according to any one of the previous embodiments (such as the first, second, third or fourth embodiments with or without the above described additional features of present invention) comprises membranes which are in spiral wound from. This ion-selective electrodialysis apparatus can have the MVA membrane forming an inner spiral wound being surrounded at least in part by a AM membrane spiral wound which is at least in part being surrounded by a CM membrane spiral wound or it can have the CM membrane forming an inner spiral wound being surrounded at least in part by a AM membrane spiral wound which is at least in part being surrounded by a MVA membrane spiral wound.

The present invention is also directed to an ion-selective electrodialysis apparatus according to any one of the previous embodiments, whereby each compartment of the at least one unit has an input and an output.

The present invention is also directed to an ion-selective electrodialysis apparatus according to any of the previous embodiments, whereby the second inner compartment or the compartment that at least in part is formed by an AM and a MVA membrane is a selector compartment to isolate a selected ion in an aqueous separator solution that at is input is foreseen to receive an aqueous fluid, preferably contains salt in desired concentration.

The present invention is also directed to an ion-selective electrodialysis apparatus according to any one of the previous embodiments, whereby the first compartment or the compartment that is at least in part formed by a CM and AM membrane that at the input is foreseen with a means to receive an ion mixture aqueous feed solution.

The present invention is also directed to an ion-selective electrodialysis apparatus according to any one of the previous embodiments, whereby the second compartment that is at least in part formed by a MVA and AM membrane at its input is foreseen with a means to receive an aqueous fluid, preferably contains salt in desired concentration.

The present invention is also directed to an ion-selective electrodialysis apparatus according to any one of the previous embodiments, whereby the first compartment that is at least in part formed by a CM and AM membrane that is at its output foreseen with a means to receive the remained of the feed solution.

The present invention is also directed to an ion-selective electrodialysis apparatus according to any one of the previous embodiments, whereby the second compartment that is at least in part formed by a AM and MVA membrane at its output foreseen with a means to receive the product solution with the selectively isolated ion or ions.

The present invention is also directed to an ion-selective electrodialysis apparatus according to any one of the previous embodiments, whereby the first compartment that is at least in part formed by a MVA and CM membrane at its output foreseen with a means to receive brine solution.

The present invention is also directed to an ion-selective electrodialysis apparatus according to any one of the previous embodiments, whereby the monovalent selective anion exchange membrane (MVA) has membrane selectivity for a divalent anion C ^" towards monovalent anion B ^" of s ξ,„„ _< = P _R = .for m-n molar of C ^2" is retained in the selector; and

m + 2(m -n)

m+2(m-n) molar of B ^" is transported through the MVA membrane.

The present invention is also directed to an ion-selective electrodialysis apparatus according to any one of the previous embodiments, further comprising pump means for generating fluid flows to the inputs.

The present invention is also directed to an ion-selective electrodialysis apparatus according to any one of the previous embodiments, further comprising an operating system to operate the different flows, whereby the operating system includes a user interface that to enable the user to interact with the functionality of the computer. Such user interface can be a wireless interface. Moreover the operating system can include a graphical user interface and whereby the operating system controls the ability to generate graphics on the computer's display device that can be displayed in a variety of manners representative for or associated with the condition of separation or concentration.

Further features on the embodiments according to the current invention, concerns one or more of the following uses:

• The use of the ion-selective electrodialysis apparatus of present invention for water purification.

• The use of the ion-selective electrodialysis apparatus f of present invention or enrichment or separartion of chromium (III) from a watery fluid.

· The use of the ion-selective electrodialysis apparatus of present invention for separation or enrichment of sulphate from sulphate/chloride mixture

• The use of the ion-selective electrodialysis apparatus of present invention for separation or enrichment of phosphorus from a watery mixture.

• The use of the ion-selective electrodialysis apparatus of present invention for separation or enrichment of fatty acids from a watery mixture

• The use of the ion-selective electrodialysis apparatus of present invention for separation or enrichment of amino acids from a watery mixture.

• The use of the ion-selective electrodialysis apparatus of present invention for separation or enrichment of proteins from a watery mixture.

· The use of the ion-selective electrodialysis apparatus of present invention for separation or enrichment of isomers from a watery mixture. • The use of the ion-selective electrodialysis apparatus of present invention for separation or enrichment of other charged compounds/particles/colloids from a watery mixture.

• The use of the ion-selective electrodialysis apparatus of present invention for separation, enrichment, or fractionation of charged inorganic ions or organic ions or compounds or particles or colloids from a watery mixture.

Another aspect of present invention concerns the use of the ion-selective electrodialysis apparatus according to any one of the previous embodiments, to generate a HxP04y- product for a struvite crystalisation process from a phosphate-rich water mixture.

Yet another aspect of present invention concerns the use of the ion-selective electrodialysis apparatus according to any one of the previous embodiments, in the pretreatment or the post- treatment of the REM-NUT process. Yet another aspect of present invention concerns a struvite separation-precipitation system, characterized in that the systems comprises reactor-crystalizer , a submerged ultrafiltration unit and on-selective electrodialysis apparatus according to any one of the previous embodiments. Having thus described several illustrative embodiments, it is to be appreciated that various modifications will readily occur to those skilled in the art within the scope of the embodiments. Accordingly, the foregoing description and attached drawings are by way of example only, and are not intended to be limiting. Drawing Description

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:

Figure 1: is a schematic view showing the principle of Selectrodialysis for separation and enrichment of multivalent anion C ^" from monovalent anion B ^" .

Figure 2: is a graphic view showing applied current, concentration of chloride and the molar ratio between sulfate and chloride as a function of time in the selector compartment. Figure 3: is a graphic view demonstrating inorganic ions concentration changes (expressed by percentage) as a function of time in the feed, product and brine compartments.

Figure 4: is a graphic view demonstrating the principle of the application of the electrodialysis of present invention, Selectrodialysis, for phosphate removal/recovery and the steams of the phosphate-rich wastewater treatment.

Figure 5: is a schematic view of multiple AM-MVA-CM selector configuration.

Figure 6: is a schematic view of the streams in electrodialysis of present invention for chromium (Ill)-rich wastewater treatment.

Figure 7: is a plot of the concentration of chloride and phosphate as a function of time in the product compartment of Selectrodialysis.

Figure 8: is a proposed struvite separation-precipitation system which includes a selectrodialysis installation, a reactor-crystalizer and a submerged ultrafiltration unit.

Figure 9: is a schematic diagram of separation and purification of tryptophan from corn fermentation broth by this innovative ion-selective electrodialysis apparatus (selectrodialysis) with loose and tight anion exchange membranes.

Figure 10: is a schematic view of an ion-selective electrodialysis apparatus, which apparatus comprises at least two units comprising at least five flow trough compartments which units are least in part are formed by a sequence or stack of membranes comprising at least two cation exchange membrane (CM), at least two standard anion exchange membrane (AM) and at least two anion selective membrane (MVA) and a whereby the apparatus further comprises an electric field generating means or electrical potential generating means, characterised in that: the compartments of the units are at least in part formed by two CM membrane and two MVA membrane and two inner separating AM membrane dividing into five compartments, whereby the first compartment that is at least in part formed by an AM membrane and a CM membrane (feed compartment, compartment 1), the second compartment is at least in part formed by a MVA membrane and an AM membrane (selector compartment, compartment 2) the third compartment is at least in part formed by a CM membrane and a MVA membrane (brine compartment, compartment 3), the forth compartment that is at least in part formed by an AM membrane and a CM membrane (feed compartment, compartment 4) and the fifth compartment is at least in part formed by a MVA membrane and an AM membrane (selector compartment, compartment 5)

Figure 11: is a schematic view of an ion-selective electrodialysis apparatus of claim 1, which apparatus comprises at least two units comprising six flow trough compartments which unit is least in part are formed by a sequence or stack of membranes comprising at least three cation exchange membranes (CM), at least two non-selective anion exchange membrane (AM) and at least two anion selective membrane (MVA) and a whereby the apparatus further comprises an electric field generating means or electrical potential generating means, characterised in that: Compartment 2 or 5, for concentrating or separating a selected ion (selector compartment), of the unit is at least in part formed by an AM membrane wall and at least in part formed by a MVA membrane wall each separating an additional compartment for a CM membrane, Compartment 1 or 4 that is at least in part formed by an AM membrane and a CM membrane (feed compartment) and Compartment 3 or 6 is at least in part formed by a MVA membrane and a CM membrane (brine compartment).

» Figure 12: is a schematic view of an ion-selective electrodialysis apparatus, which apparatus comprises at least two units comprising at least five flow trough compartments which units are least in part are formed by a sequence or stack of membranes comprising at least two cation exchange membrane (CM), at least two non-selective anion exchange membrane (AM) and at least two anion selective membrane (MVA) and a whereby the apparatus further comprises an electric field generating means or electrical potential generating means, whereby: Compartment 2 or 5, for concentrating or separating a selected ion (selector compartment), of the unit is at least in part formed by a MVA membrane wall and at least in part formed by an AM membrane wall each separating an additional compartment for a CM membrane, Compartment 1 or 4 that is at least in part formed by a MVA membrane and a CM membrane (feed compartment) and Compartment 3 or 6 is at least in part formed by an AM membrane and a CM membrane (brine compartment).

• Figure 13: is a schematic view of an ion-selective electrodialysis apparatus, which apparatus comprises at least two units comprising at least five flow trough compartments which units are least in part are formed by a sequence or stack of membranes comprising at least two cation selective membrane (MVC), at least two standard cation exchange membrane (CM) and at least two standard anion exchange membrane (AM) and a whereby the apparatus further comprises an electric field generating means or electrical potential generating means, characterised in that: the compartments of the units are at least in part formed by two AM membrane and two MVC membrane and two inner separating CM membrane dividing into five compartments, whereby the first compartment that is at least in part formed by an AM membrane and a CM membrane (feed compartment, compartment 1), the second compartment is at least in part formed by a CM membrane and a MVC membrane (selector compartment, compartment 2), the third compartment is at least in part formed by a MVC membrane and a AM membrane (brine compartment, compartment 3), the forth compartment that is at least in part formed by an AM membrane and a CM membrane (feed compartment, compartment 4) and the fifth compartment is at least in part formed by a CM membrane and a MVC membrane (selector compartment, compartment 5)

• Figure 14: is a schematic view of an ion-selective electrodialysis apparatus of claim 1, which apparatus comprises at least two units comprising six flow trough compartments which unit is least in part are formed by a sequence or stack of membranes comprising at least three cation exchange membranes (CM), at least two non-selective anion exchange membrane (AM) and at least two cation selective membrane (MVC) and a whereby the apparatus further comprises an electric field generating means or electrical potential generating means, characterised in that : compartment 2 or 5 that is at least in part formed by an AM membrane and a CM membrane (feed compartment), compartment 3 or 6, for concentrating or separating a selected ion (selector compartment), of the unit is at least in part formed by a CM membrane wall and at least in part formed by a MVC membrane and cCompartment 1 and 4 are the brine compartments

· Figure 15: is a schematic view of an ion-selective electrodialysis apparatus, which apparatus comprises at least two units comprising at least five flow trough compartments which units are least in part are formed by a sequence or stack of membranes comprising at least two cation exchange membrane (CM), at least two non-selective anion exchange membrane (AM) and at least two cation selective membrane (MVC) and a whereby the apparatus further comprises an electric field generating means or electrical potential generating means, whereby: compartment 2 or 5 that is at least in part formed by an AM membrane and a MVC membrane (feed compartment), compartment 3 or 6, for concentrating or separating a selected ion (selector compartment), of the unit is at least in part formed by a MVC membrane wall and at least in part formed by a CM membrane and compartment 1 and 4 are the brine compartments.

In interpreting these claims, it should be understood that:

a) the word "comprising" does not exclude the presence of other elements or acts than those listed in a given claim;

b) the word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements;

c) any reference signs in the claims do not limit their scope;

d) several "means" may be represented by the same item or hardware or function; g) any of the disclosed devices or portions thereof may be combined together or separated into further portions unless specifically stated otherwise;

h) no specific sequence of acts is intended to be required unless specifically indicated; and i) the term "plurality of an element includes two or more of the claimed element, and does not imply any particular range of number of elements; that is, a plurality of elements can be few as two elements.