PROCESS TO SEPARATE AN AQUEOUS FEED

Abstract

The invention is directed to a process for separating an aqueous feed comprising of dissolved ammonium bicarbonate. The process comprises: a step (a) in which an electrodialysis is performed to obtain a diluate and a concentrate comprising of ammonium bicarbonate and a step (b) in which the total ammonia nitrogen (TAN) as present in the concentrate is separated from the bicarbonate ions as present in the concentrate by means of a bipolar membrane electrodialysis to a total ammonia nitrogen (TAN) alkaline fraction and a bicarbonate acid fraction.

Claims

1. A process for separating an aqueous feed comprising of dissolved ammonium bicarbonate by (a) performing an electrodialysis in an electrodialysis unit wherein ions are transported via a membrane from the aqueous feed under influence of a positive and negative electrode to a mineral poor aqueous solution to obtain a concentrate comprising of ammonium bicarbonate and wherein the remaining aqueous feed is obtained as a diluate, wherein the electrodialysis unit does not comprise a bipolar membrane, (b) separating the total ammonia nitrogen (TAN) as present in the concentrate from the bicarbonate ions as present in the concentrate by means of a bipolar membrane electrodialysis as performed in a bipolar membrane electrodialysis system to a total ammonia nitrogen (TAN) alkaline fraction and a bicarbonate acid fraction, wherein in step (b) the bipolar membrane electrodialysis system is of a three chamber type with bipolar membranes (BPM), an anion exchange membranes (AEM) and a cation exchange membranes (CEM), wherein the bicarbonate ions pass the anion exchange membrane to become the bicarbonate acid fraction, wherein the ammonium ions of the total ammonia nitrogen (TAN) pass the cation exchange membrane to become the total ammonia nitrogen (TAN) alkaline fraction and wherein the remaining concentrate is obtained as a third remaining aqueous fraction, which third remaining aqueous fraction is recycled to the electrodialysis of step (a) to be used as the mineral poor aqueous solution where it picks up the ammonium bicarbonate to become the concentrate or wherein in step (b) the bipolar membrane electrodialysis system is of a two chamber type with bipolar membranes (BPM) and cation exchange membranes (CEM), wherein the ammonium ions of the total ammonia nitrogen (TAN) pass the cation exchange membrane to become the total ammonia nitrogen (TAN) alkaline fraction and wherein the remaining concentrate becomes the bicarbonate acid fraction, wherein part of the bicarbonate in the bicarbonate acid fraction is separated as carbon dioxide to obtain an aqueous fraction poor in bicarbonate which aqueous fraction poor in bicarbonate is recycled to the electrodialysis of step (a) to be used as the mineral poor aqueous solution where it picks up the ammonium bicarbonate to become the concentrate.

2. The process according to claim 1, wherein the electrodialysis is performed by applying a polarity between two electrodes and wherein periodically the polarity of the electrodes is reversed.

3. The process according to claim 1, wherein the bipolar membrane electrodialysis system is of the three chamber type and wherein the bipolar membrane electrodialysis of step (b) is performed in a stack of between 1 and 200 cell triplets present between an anode and a cathode, wherein each cell triplet comprises the bipolar membrane (BPM), the anion exchange membrane (AEM) and the cation exchange membrane (CEM) and wherein a spacer is present between the anion exchange membrane (AEM) and the cation exchange membrane (CEM) such that the distance between the anion exchange membrane (AEM) and the cation exchange membrane (CEM) is between 0.1 and 10 mm.

4. The process according to claim 1, wherein the bipolar membrane electrodialysis system is of the two chamber type and wherein the bipolar membrane electrodialysis of step (b) is performed in a stack of between 1 and 200 cell pairs present between an anode and a cathode, wherein each cell pair comprises the bipolar membrane (BPM) and the cation exchange membrane (CEM) and wherein the distance between bipolar membrane (BPM) and the cation exchange membrane (CEM) is between 0.1 and 10 mm.

5. The process according to claim 1, wherein the aqueous feed comprises solids and preferably between 0.1 and 5 wt % solids and wherein substantially all of the solids of the feed end up in the diluate.

6. The process according to claim 5, wherein more than 95 wt % of the solids in the aqueous feed have a dynamic diameter of less than 50 m, preferably less than 5 m.

7. The process according to claim 1, wherein the aqueous feed comprises bivalent and/or trivalent ions and/or cations.

8. The process according to claim 7, wherein the aqueous feed comprises phosphate, magnesium, calcium, potassium and bicarbonate ions and total ammonia nitrogen (TAN) and wherein in the electrodialysis step (a) the majority of the phosphate, magnesium and calcium ions remain in the diluate and wherein the majority of the total ammonia and bicarbonate ions and potassium ions end up in the concentrate.

9. The process according to claim 1, wherein in a next step (c) ammonia is separated from the total ammonia nitrogen (TAN) alkaline fraction by means of a membrane stripping process using an acidic aqueous solution as a stripping medium thereby obtaining an aqueous solution of ammonium salt.

10. The process according to claim 9, wherein the acidic aqueous solution is a sulfuric acid aqueous solution or a nitric acid aqueous solution.

11. The process according to claim 8, wherein the aqueous feed is the liquid fraction of manure or a waste water fraction.

12. (canceled)

13. The process according to claim 8, wherein the waste water is obtained in an anaerobic treating process of municipal or industrial wastewater and/or the aqueous feed is reject water obtained in a sludge dewatering process as part of a wastewater treatment plant.

14. (canceled)

15. A process to separate manure comprising of an aqueous suspension of solid particles comprising of organic bound nitrogen and total ammonia nitrogen (TAN) by performing the following steps (i) separating the majority of the solids from the aqueous suspension such to obtain a first wet solids fraction rich in organic bound nitrogen and a first aqueous fraction rich in total ammonia nitrogen (TAN) and solid particles, (ii) separating the majority of the solid particles from the first aqueous fraction to obtain a second aqueous fraction poor in solids and a second solids fraction, and (iii) separating the second aqueous fraction comprising of dissolved ammonium bicarbonate by the process according to claim 1.

16. The process according to claim 15, wherein the solid content of the first wet solids fraction obtained in step (i) is between 5 and 40 wt %.

17. The process according to claim 15, wherein at least 60% of the solids as present in the aqueous suspension is comprised in first wet solids fraction.

18. The process according to claim 15, wherein the manure has been subjected to an anaerobic digestion process before being treated in step (i).

19. The process according to claim 15, wherein the mass flows for nitrogen, phosphorus and potassium are measured in step (i) and in step (ii) and shared on line with a central monitoring organization for administrative and/or commercial purposes.

20. A process configuration comprising an electrodialysis unit, a bipolar membrane electrodialysis unit and a membrane stripping unit, wherein the electrodialysis unit has an outlet for a concentrate which is fluidly connected to the bipolar membrane electrodialysis unit and wherein the electrodialysis unit does not comprise a bipolar membrane, wherein the bipolar membrane electrodialysis unit is of a three chamber type with bipolar membranes (BPM), an anion exchange membranes (AEM) and a cation exchange membranes (CEM), or wherein the bipolar membrane electrodialysis system is of a two chamber type with bipolar membranes (BPM) and cation exchange membranes (CEM), and wherein the bipolar membrane electrodialysis unit has an outlet for a total ammonia nitrogen (TAN) alkaline fraction.

21. The process configuration according to claim 20, wherein the electrodialysis unit is an electrodialysis reversal (EDR) unit.

22. The process configuration according claim 20, wherein the outlet for a total ammonia nitrogen (TAN) alkaline fraction is fluidly connected to the membrane stripping unit and wherein the membrane stripping unit has an inlet for an aqueous acid feed and an outlet for an aqueous ammonium salt product.

23. A manure recycle process configuration comprising of a first separator in which a manure comprising of an aqueous suspension of solid particles comprising of organic bound nitrogen and total ammonia nitrogen (TAN) is separated into a first wet solids fraction rich in organic bound nitrogen as a first fertiliser and a first aqueous fraction rich in total ammonia nitrogen (TAN) and solid particles, a second separator suited to separate the majority of the solid particles from the first aqueous fraction by means of filtration to obtain a second aqueous fraction poor in solids and a second solids fraction as a second fertiliser, and a process configuration according to claim 20.

24. (canceled)

Description

[0109] The invention will be illustrated by FIGS. 1-6.

[0110] FIG. 1 shows a manure recycle process configuration or system suited to perform the process according to this invention. The invention is also directed to such a manure recycle process system comprising of [0111] a first separator (3) in which a manure (2) comprising of an aqueous suspension of solid particles comprising of organic bound nitrogen and total ammonia nitrogen (TAN) is separated into a first wet solids fraction (4) rich in organic bound nitrogen as a first fertiliser and a first aqueous fraction (5) rich in total ammonia nitrogen (TAN) and solid particles, [0112] a second separator (6) suited to separate the majority of the solid particles from the first aqueous fraction (5) by means of filtration to obtain a second aqueous fraction poor in solids (8) and a second solids fraction (7) as a second fertiliser, [0113] a combined electrodialysis unit and bipolar membrane electrodialysis unit (9) separates the second aqueous fraction poor in solids (8) into a diluate (11) as a fertiliser, a total ammonia nitrogen (TAN) alkaline fraction (12) and a bicarbonate acid fraction (14).

[0114] The combined electrodialysis unit and bipolar membrane electrodialysis unit (9) may also comprise a membrane vacuum separator to obtain a gaseous ammonia/water mixture (10) from part of the alkaline fraction (12). This gaseous ammonia/water mixture (10) may be used to generate electricity in fuel cell (16).

[0115] The manure recycle process configuration may further comprise an ammonium salt processing unit (13) in which all or part of the alkaline fraction (12) rich in total ammonia nitrogen (TAN) is contacted with sulfuric acid and/or nitric acid (13a) to obtain an aqueous solution (15) of ammonium sulphate or ammonium nitrate as a eighth fertiliser.

[0116] The manure recycle process system may further comprise a carbon dioxide reclaiming unit (26) where carbon dioxide (27) is reclaimed from the bicarbonate acidic fraction (14) to obtain a less acidic aqueous fraction (28).

[0117] The manure recycle process system may further comprise of a holding vessel T1 (1) for manure, a holding vessel T2 (21) for the first fertiliser and optionally combined with the second fertiliser, a holding tank T3 (20) for the third fertiliser and a holding tank T4 (19) for the eighth fertiliser (15). From these holding tanks T1-T4 an optimal fertiliser (31) may be blended using a blending unit (30). The blended fertiliser (31) may be used as a fertiliser for growing grass (22). This grass (23) is subsequently consumed by cows (24) generating manure (25) which is stored in holding vessel T1 (1) thereby closing the cycle.

[0118] FIG. 2 shows the combined electrodialysis unit and bipolar membrane electrodialysis unit (9) and ammonium salt processing unit (13) of FIG. 1 in more detail. The figure shows a process scheme consisting of an electrodialysis unit (41), a bipolar membrane electrodialysis unit (42) and a membrane stripping unit (43). The electrodialysis unit (41) has an inlet (44) for reject water (45), an outlet (46) for a concentrate (47) and an outlet (48) for a diluate (49). In diluate (49) almost all of the solids and most of the phosphate ions, magnesium cations and calcium cations will be present. The majority of the total ammonia nitrogen (TAN) and bicarbonate ions and potassium ions end up in a concentrate (47). The outlet (46) for a concentrate (47) is fluidly connected to a bipolar membrane electrodialysis unit (42a). The bipolar membrane electrodialysis unit (42a) of

[0119] FIG. 2 is a unit of the two chamber type wherein each cell pair comprises a bipolar membrane (BPM) and an anion exchange membrane (AEM). In such a unit (42a) bicarbonate ions will predominantly pass the anion exchange membranes (AEM) to become a bicarbonate acid fraction (51). The starting concentrate (47) will the become the total ammonia nitrogen (TAN) alkaline fraction (52). The majority of the ammonium and potassium cations as present in the concentrate (47) thus do not pass a membrane and remain in the aqueous fraction (52). An outlet (53) for the total ammonia nitrogen (TAN) alkaline fraction (52) is fluidly connected to the membrane stripping unit (43). To membrane stripping unit (43) an aqueous acid feed (54) is fed via inlet (54a). Ammonia will pass the membrane of the membrane stripping unit (43) resulting in an aqueous ammonium salt product (50). This aqueous ammonium salt product is discharged from the membrane stripping unit via an outlet (55). The aqueous remaining fraction (56) poor in total ammonia nitrogen (TAN) is recycled back to the electrodialysis unit (41) where it picks up fresh ammonium bicarbonate and potassium to become the concentrate (47). A purge (57) is present downstream the ammonium membrane stripping unit (43) and upstream the electrodialysis unit (41) to avoid build up of non-separated compounds. Carbon dioxide (58) is separated from the bicarbonate acid fraction (51) in degassing unit (59). The remaining aqueous fraction (60) is recycled to the bipolar membrane electrodialysis unit (42). A purge (57a) is present downstream degassing unit (59) to avoid build up of non-separated compounds, such as acids.

[0120] FIG. 3 shows a process scheme consisting of an electrodialysis unit (41), a bipolar membrane electrodialysis unit (42) and a membrane stripping unit (43) as in FIG. 2. The difference is that the bipolar membrane electrodialysis unit (42b) of FIG. 3 is a unit of the two chamber type wherein each cell pair comprises a bipolar membrane (BPM) and an cation exchange membrane (CEM). In such a unit (42b) ammonium and potassium cations will predominantly pass the cation exchange membranes (CEM) to become the total ammonia nitrogen (TAN) alkaline fraction (61). The bicarbonate ions as present in the concentrate (47) thus do not pass a membrane and will remain in the aqueous fraction to become bicarbonate acid fraction (62). An outlet (63) for the total ammonia nitrogen (TAN) alkaline fraction (61) is fluidly connected to the membrane stripping unit (43). To membrane stripping unit (43) an aqueous acid feed (54) is fed. Ammonia will pass the membrane of the membrane stripping unit (43) resulting in an aqueous ammonium salt product (50). This aqueous ammonium salt product is discharged from the membrane stripping unit via an outlet (55). The aqueous remaining fraction (64) poor in total ammonia nitrogen (TAN) is recycled back to the bipolar membrane electrodialysis unit (42) where it picks up fresh ammonium bicarbonate and potassium to become the total ammonia nitrogen (TAN) alkaline fraction (61). Carbon dioxide (58) is separated from the bicarbonate acid fraction (62) in degassing unit (59). The remaining aqueous fraction (65) is recycled to the electrodialysis unit (41). A purge (57b) is present downstream the membrane stripping unit (43) to avoid build up of non-separated compounds, such as potassium ions. A purge (57c) is present downstream degassing unit (59) and upstream the electrodialysis unit (41) to avoid build up of non-separated compounds, such as acids.

[0121] FIG. 4 shows a process scheme for an exemplary aqueous feed comprising of solids, ammonium bicarbonate, phosphate ions, magnesium cations and calcium cations as obtained from a sludge dewatering process as part of a wastewater treatment plant. The process scheme consisting of an electrodialysis unit (41), a bipolar membrane electrodialysis unit (42) and a membrane stripping unit (43) as in FIG. 2. The difference is that the bipolar membrane electrodialysis unit (42c) of FIG. 4 is a unit of the three chamber type wherein each cell pair comprises a bipolar membrane (BPM), an anion exchange membrane (AEM) and a cation exchange membrane (CEM). In such a unit (42c) ammonium and potassium cations will predominantly pass the cation exchange membranes (CEM) to become the total ammonia nitrogen (TAN) alkaline fraction (71), bicarbonate ions will predominantly pass the anion exchange membranes (AEM) to become a bicarbonate acid fraction (72). The starting concentrate (47) will the become a third remaining aqueous fraction (73) poorer in total ammonia nitrogen (TAN) and bicarbonate ions. An outlet (74) for the total ammonia nitrogen (TAN) alkaline fraction (71) is fluidly connected to the membrane stripping unit (43). To membrane stripping unit (43) an aqueous acid feed (54) is fed. Ammonia will pass the membrane of the membrane stripping unit (43) resulting in an aqueous ammonium salt product (50). This aqueous ammonium salt product is discharged from the membrane stripping unit via an outlet (55). The aqueous remaining fraction (75) poor in total ammonia nitrogen (TAN) is recycled back to the bipolar membrane electrodialysis unit (42c) where it picks up fresh ammonium bicarbonate and potassium to become the total ammonia nitrogen (TAN) alkaline fraction (71). Carbon dioxide (58) is separated from the bicarbonate acid fraction (72) in degassing unit (59). The third remaining aqueous fraction (76) is recycled to the electrodialysis unit (41). A purge (57d) is present to avoid build up of non-separated compounds. A purge (57d) is present to avoid build up of non-separated compounds in the third remaining aqueous fraction (73). A purge (57e) is present downstream degassing unit (59) to avoid build up of non-separated compounds, such as acids. A purge (57f) is present downstream the membrane stripping unit (43) to avoid build up of non-separated compounds, such as potassium ions.

[0122] The invention will be illustrated by the following non-limiting examples.

EXAMPLE 1

[0123] Raw cow manure was separated using a screw press into a first wet solids fraction and an aqueous fraction rich in total ammonia nitrogen (TAN) and solid particles. This aqueous solution was filtered using a series of bag filters with the smallest pore size being 5 micron to obtain the second aqueous fraction. The TAN concentration of the second aqueous fraction was 2.57 g/L.

[0124] The experimental BPMED set-up was a bench-scale PC-Cell 64004 ED cell, consisting of a Pt/Ir-MMO coated and Ti-stretched metal anode and a stainless-steel cathode, both with a surface area of 88 cm2. The BPMED system was of the three-chamber type. The membranes and electrodes were separated by 0.5 mm thick wire mesh spacers with a void fraction of 59% made from silicon/polyethylene sulfone to form diluate, acid and base (flow) cells and electrode rinse compartments. The cell contained a BPMED membrane stack consisting of ten cell triplets as described in more detail in Bipolar membrane electrodialysis for energetically competitive ammonium removal and dissolved ammonia production, Niels van Linden, Giacomo L. Bandinu, David A. Vermaas, Henri Spanjers, Jules B. van Lier, Journal of Cleaner Production, Elsevier, 20 Jun. 2020.

[0125] The voltage between anode and cathode was held at 20 V constant. The separation was performed as a batch process wherein the aqueous fraction is recycled over the BPMED stack and wherein in time this fraction becomes a solid particle comprising aqueous fraction poor in total ammonia nitrogen (TAN) and poor in bicarbonate. The acid and alkaline fractions as present between respectively the AEM and BPM and BPM and CEM membranes are also recycled to obtain in time the bicarbonate acid fraction and the alkaline fraction rich in total ammonia nitrogen (TAN).

[0126] After 134 minutes the three streams were analysed. The pH of the obtained aqueous bicarbonate acidic fraction was 1.59. The pH of the aqueous alkaline fraction was 12.55. The content of NH.sub.3 in the aqueous alkaline fraction was 1.0 g/L. The TAN concentration in the third remaining fraction was 1.35 g/L . 47% of the TAN was thus removed from the feed of the BPMED. Energy required to remove one kg of N was 63 MJ/kg. An even more improved separation may be achieved using BPMED membrane stacks consisting of more cell triplets. Almost all of the phosphate ions remained in the third remaining fraction. The majority of potassium ions were found in the alkaline fraction.

EXAMPLE 2

[0127] Example 1 was repeated except that the starting manure was a suspension obtained after co-digesting pig manure. The TAN concentration of the second aqueous fraction was 4.67 g/L. After 98 minutes the three streams were analysed. The pH of the obtained aqueous bicarbonate acidic fraction was 2.14. The pH of the aqueous alkaline fraction was 12.64. The content of NH.sub.3 in the aqueous alkaline fraction was 4.41 g/L. The TAN concentration in the third remaining fraction was 1.04 g/L. 79% of the TAN was thus removed from the feed. Energy required to remove one kg of N was 26 MJ/kg. An even more improved separation may be achieved using BPMED membrane stacks consisting of more cell triplets. Almost all of the phosphate ions remained in the third remaining fraction. The majority of potassium ions were found in the alkaline fraction.

EXAMPLE 3

[0128] In this example a three-compartment bipolar membrane electrodialysis (BPMED-3C) configuration was compared to a two-compartment bipolar membrane electrodialysis configuration with only cation exchange membranes (BPMED-2C-C) for an ammonium bicarbonate solution having a TAN concentration of 5 g/L. The three-compartment bipolar membrane electrodialysis (BPMED-3C) configuration had the same dimensions and membranes as described in Example 1. The two-compartment bipolar membrane electrodialysis configuration was as the three-compartment bipolar membrane electrodialysis (BPMED-3C) configuration except that the ion-exchange membranes were absent and only cation exchange membranes (BPMED-2C-C) were present.

[0129] The results showed that the BPMED-2C-C configuration had a lower energy consumption to achieve approximately 90% TAN removal compared to the energy consumption of the BPMED-3C configuration achieving 90% TAN removal. The energy consumption for the BPMED-2C-C was 3.5 MJ per kilogram nitrogen removed and for the BPMED-3C 4.9 MJ per kilogram nitrogen removed. Furthermore, the use of a BPMED-2C-C allowed for more efficient recovery of TAN as NH.sub.3 in the alkaline fraction, compared to the BPMED-3C configuration. For the BPMED-2C-C configuration, at 66% TAN removal, 77% of the TAN was present as NH.sub.3 in the alkaline fraction, while for the BPMED-3C configuration, at 72% TAN removal, only 50% of the TAN was present as NH.sub.3 in the alkaline fraction and more NH3 was present in the bicarbonate acidic fraction. The higher NH.sub.3 content further allowed for a more efficient separation of ammonia from the alkaline fraction.

EXAMPLE 4

[0130] The experimental ED-BPMED-VMS set-up consisted of two bench-scale PC-Cell 64004 cells placed in series, followed up by a VMS module. In the first cell an ED stack of 10 cell pairs was present and in the second cell a BPMED stack of 4 triplets (3 chamber) was present. Both cells had an electrode surface area of 88 cm2.

[0131] Co-digested pig manure was first filtered using bag filters to obtain an aqueous feed comprising particles having a size of smaller than 20 micron. This solution was used as feed to the first cell. The initial TAN concentration of the aqueous feed was 6.6 g/L. The duration of the experiment was similar to Example 2. The TAN concentration in the feed was lowered to 1.58 g/L (concentration of resulting diluate). 80% of the TAN was thus removed from the aqueous feed. The concentrate was subsequently separated into an alkaline and bicarbonate fraction in the BPMED cell where a 100% recovery of TAN was achieved.

EXAMPLE 5

[0132] Example 4 was repeated except that only a BPMED cell was present. No ED stack was present. In order to achieve the same 80% removal of TAN a BPMED cell stack was required having a 40% higher bipolar membrane area.

EXAMPLE 6A

[0133] In an ED installation having a membrane stack of thirty cell pairs with a 1,000 cm2 electrode area 30 liter of a liquid fraction of raw pig manure was separated into a diluate and a concentrate. The liquid fraction contained 4 g/L of TAN concentration and contained particles having a size of less than 20 micron. The ED installation was operated to consistently achieve a removal of TAN of higher than 75%. The resistance of the membrane stack was measured during the treatment of the first batch of 30 L. The results are presented in FIG. 5 as the diamonds. Without cleaning the membrane stack a second batch of 30 liters of the liquid fraction of raw pig manure was separated into a diluate and a concentrate such to achieve a 75% removal of TAN. The resistance of the membrane stack was measured again during the treatment of the second batch of 30 L. The results are presented in FIG. 5 as the squares. Without cleaning the membrane stack a third batch of 30 liters of the liquid fraction of raw pig manure was separated into a diluate and a concentrate such to achieve a 75% removal of TAN. Again, during the treatment of the third batch of 30 L, the resistance of the membrane stack was measured. The results are presented in FIG. 5 as the triangles. It is observed that the resistance increases after every batch indicating membrane fouling.

EXAMPLE 6B

[0134] The resistance of the membrane stack was measured as described in Example 6a. After the three treated batches in Example 6a, the polarity of the electrodes was reversed, as well as the flow directions of the diluate and concentrate solutions. The measured resistance is shown in FIG. 6. In FIG. 6 the circles are the measurements of the membrane resistance before performing the experiment at the reversed polarity and the squares are the measurements of the membrane resistance after performing the experiment and the application of polarity reversal. This shows that by applying this so called electrode polarity reversal option, also referred to as electrodialysis reversal (EDR), fouled membranes can be restored.

EXAMPLE 6C

[0135] Without cleaning the membrane stack of Example 6b a batch of 30 liters of the liquid fraction of raw pig manure was separated into a diluate and a concentrate according to Example 6a. The resistance of the membrane stack was measured during the treatment. Subsequently, the EDR function was applied and another batch of 30 liters of the liquid fraction of raw pig manure was separated into a diluate and concentrate according to Example 6a. By applying the EDR function between the treatment of two consecutive batches, about the same resistance was measured during the second batch as compared to the resistance measured during the first batch indicating that no or very little fouling occurred.

EXAMPLE 7

[0136] An aqueous NH.sub.3 solution having a 10 g/L TAN concentration was continuously recirculated over a hydrophobic membrane within a membrane housing of a vacuum membrane separator (VMS) module as described in Niels van Linden, Henri Spanjer, Jules B. van Lier, Fuelling a solid oxide fuel cell with ammonia recovered from water by vacuum membrane stripping, Chemical Engineering Journal, Volume 428, 15 Jan. 2022, 131081.A vacuum was applied by a vacuum pump on the permeate side of the hydrophobic membrane, which allowed for NH.sub.3 gas and water vapor to be transported to the permeate side. After passing the vacuum pump the obtained gaseous mixture was condensed in a cool trap to obtain a condensed NH.sub.3 aqueous solution having a TAN concentration of 34 g/L . Thus a concentration factor of 3.4 was obtained. In a next experiment water was condensed before the vacuum pump in a cool trap at the vacuum pressure conditions. The thus condensed water was separated from the remaining gas. The remaining gas was subsequently condensed at atmospheric pressure after the vacuum pump as above to obtain an aqueous solution having a TAN concentration of 58.4 g/L. Thus a concentration factor of 5.8 was obtained.