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Desalination of glutamine fermentation broth by electrodialysis
Process Biochemistry 41 (2006) 716–720 www.elsevier.com/locate/procbio
Short communication
Desalination of glutamine fermentation broth by electrodialysis Jin-Yu Shen a,*, Jing-Ran Duan a, Li-Xin Yu a, Xin-Hui Xing a, Ping Xu b,* a b
Department of Chemical Engineering, Tsinghua University, Beijing 100084, PR China State Key Lab of Microbial Technology, Shandong University, Jinan 250100, PR China
Received 15 May 2005; received in revised form 31 July 2005; accepted 2 August 2005
Abstract An electrodialytic process was proposed to achieve an efficient desalination of glutamine (Gln) fermentation broth. Several electrodialytic experiments using different combinations of anion- and cation-exchange membranes were carried out, and a set of satisfactory combination of membranes was selected for the desalination. The effects of operational current density and pH on desalination and glutamine recovery were investigated and discussed. The electrical current efficiency and the energy consumption were also studied. The loss of glutamine could be reduced effectively when the current density was kept at 204 A/m2 and pH was controlled near the isoelectric point of glutamine (pI: 5.65) during the process. The clear solution after this electrodialytic desalination can meet the further simple separation of glutamine from the solution using anion-exchange resin. # 2005 Elsevier Ltd. All rights reserved. Keywords: Electrodialysis; Ion-exchange membrane; Fermentation broth; Glutamine; Desalination; Separation
1. Introduction Glutamine (Gln) is the g-carboxylic amidate of glutamic acid (Glu) and it is the most abundant amino acid in the body [1]. In recent years many researches on medical treatment and health care have shown that glutamine is becoming a very promising drug [2,3] and a healthy food ingredient [4], and its industrialization has considerable perspective. Separation process of glutamine from the fermentation broth is the primary factor, which restricts its production cost. And high concentration of inorganic salt, for example, sulfate in the fermentation broth influences the separation of glutamine greatly. However, high concentration of ammonium sulfate (about 6%) should be used to ferment good production of glutamine in broth. The recovery of glutamine from the fermentation broth is low during the traditional dual-columnar separation process of anion- and cationexchange resins because glutamine tends to transform into glutamic acid on both the high acidic and high alkaline resins [5]. Furthermore, much water is required for the * Corresponding authors. Tel.: +86 10 62788568; fax: +86 10 62770304. E-mail addresses: [email protected] (J.-Y. Shen), [email protected] (P. Xu). 1359-5113/$ – see front matter # 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.procbio.2005.08.001
reactivation and washing of the ion-exchange resin, imposing a big burden on wastewater treatment. In order to solve the above problems, we raised an electrodialytic desalination of glutamine fermentation broth, which was easy to separate glutamine by the following single anionexchange columnar process. It should be a promising process for efficient recovery of glutamine from the fermentation broth to cut down the operational cost.
2. Materials and methods 2.1. Reagents, broth and membranes Standard glutamine (pI: 5.65) and glutamic acid (pI: 3.22) [6] were purchased from Sigma (Purity > 99%). Glutamine fermentation broth by Corynebacterium glutamicum ATCC 13032 was provided by State Key Laboratory of Microbial Technology, Shandong University. The ionexchange membranes used in the experiments were provided by Tokuyama Company of Japan. The types of membranes TH1–TH4 used in the study were AM-1 A0039 (0.13–0.16 mm thickness, strong acidic Na type), AMI
J.-Y. Shen et al. / Process Biochemistry 41 (2006) 716–720
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(0.16–0.20 mm thickness, strong acidic Na type), CM*C0473 (0.12–0.16 mm thickness, strong alkaline Cl type) and CM-1 C-0683 (0.14–0.18 mm thickness, strong alkaline Cl type), respectively.
following formula:
2.2. Analytical methods
where c, F, i, I, t, V, Z and t were referred to solution concentration (mol l1), Faraday’s constant (96,486 Coulomb mol1), the number of compartments, electrical current (A), time (s), solution volume (l), ionic valence number and duration time, respectively [8]. The specific energy consumption e (kW h kg1 sulfate) was estimated from voltage, current, duration, etc. [9] and calculated by the equation as follows:
Glutamine and glutamic acid were determined by a biosensor (Model 2700, YSI, USA). The sulfate analysis was carried out by an ion chromatography (HIC-6 A, Shimadzu, Japan) [7]. 2.3. Pretreatment of fermentation broth The chemical component of the fermentation broth before the pretreatment was 42.0 g l1 glutamine, 5.5 g l1 glutamic acid, 2.0 g l1 glucose, 0.45 M sulfate and 0.05 M of phosphates, pH 6.0. Through pretreatment of the broth by combination of flocculation and ultrafiltration processes, lots of cells, proteins and amylose were removed. Then the broth was decolored using active carbon. Except for a few of cells, proteins, amyloses, and pigments, the main ingredients of the fermentation broth after the pretreatment were 40.0 g l1 glutamine, 5.0 g l1 glutamic acid, 1.8 g l1 glucose, 0.42 M sulfate and 0.05 M of phosphates, pH 6.0. The fermentation broth after pretreatment was used in the following experiments. 2.4. Experimental The experiments were carried out in the laboratorial electrodialyser consisting of seven compartments with alternating cation- and anion-exchange membranes, which was a self-made apparatus. Each compartment contained a 20 cm 10 cm ion-exchange membrane with an effective area of 98 cm2, and between every two compartments was a 0.8 mm polypropylene double-layered mesh grid partition. The electrical potential was applied between the two electrodes by means of an ac–dc rectifier having a variable current capacity of 0–8.2 A and a variable voltage of 0– 31.1 V. And the operation could be done under a constant voltage or constant current condition. Under the direct current condition, cations (such as NH4+and Na+) would migrate toward the cathode and anions (such as SO42 and Cl) toward the anode. Glutamine would not migrate at its isoelectric point because it was amphoteric electrolyte. Therefore, the concentration of inorganic salts was reduced greatly, whereas glutamine still existed in the initial feed solution. The performance of an electrodialytic process can be evaluated by the so-called current efficiency (h) and the specific energy consumption (e) of a given run. Current efficiency is defined as the overall efficiency of current utilization in transporting salts from the diluent stream to the concentrate stream and is usually expressed as a percentage. In this paper, current efficiency (h) was calculated by the
P DðZcVÞi F h ¼ Ri t 0 IðtÞdt
Rt e¼
0
’ðtÞIðtÞdt Dms
(1)
(2)
where the symbols w and Dms were defined as operating voltage and mass quantity transported, respectively; and the other symbols were as the same as in formula (1) [10].
3. Results and discussion 3.1. Effects of ion-exchange membranes on desalination The experiments were carried out under the uniform conditions except for in various combinations of anion- and cation-exchange membranes. The electrodialysis was performed at a constant current of 6 A, which was equivalent to a current density 204 A/m2. The electrodialytic operation was controlled under pH 5.6 0.5. The desalination with various combinations of ionexchange membranes were shown in Fig. 1. The loss of glutamine for combinations C and D was less (13 and 19%, respectively) than combinations A and B (24 and 33%, respectively) at the same salt removal ratio (95%). The differences in the loss of glutamine might be due to the structures of different ion-exchange membranes. At pH 5.65, glutamine existed mostly as electroneutral dipole ions. Glutamine could penetrate membrane through molecular diffusion because of its concentration gradients between the feed compartment and the salt compartment. Although sulfate removal rates were higher in combinations A and B than in the others, the selectivity of the membranes was poor and the recovery of glutamine was low. The membrane selectivity to inorganic salts in combination C was the best in all combinations. The loss of glutamine for combination C was the least (13%), but the operation time was the longest (393 min). Meanwhile, the operation time for combination D was 279 min and the glutamine loss was 19% at the same salt removal ratio (95%). Combination D was selected for further experiments considering various factors such as operation time and loss of product.
718
J.-Y. Shen et al. / Process Biochemistry 41 (2006) 716–720
Fig. 1. Profile of electrodialytic desalination with various combinations: (A) TH1–TH3; (B) TH1–TH4; (C) TH2–TH3; and (D) TH2–TH4.
3.2. Removal ratio of ammonium sulfate with change of current and voltage Fig. 2 showed that the salt concentration changed and the resistance of the stack increased gradually during the electrodialytic process of the fermentation broth with control of pH (5.6 0.5). Therefore, the voltage was adjusted to keep the constant current density (204 A/m2). The voltage reached the highest value of the direct current power supplier (31.1 V) when the salt removal ratio in fermentation broth was 70%. Later, the current density
Fig. 2. Removal ratio of ammonium sulfate with change of current and voltage.
began to fall. The salt removal ratio in fermentation broth reached nearly 95% when the current density fell to 31 A/ m2. Therefore, the end point of the eletrodialytic desalination could be estimated according to the value of current density. 3.3. Effect of pH on loss of glutamine Electrodialytic desalination was carried out under the 204 A/m2 current density without pH control of the fermentation broth as shown in Fig. 3. At the beginning
Fig. 3. Time profile of electrodialytic desalination process of the fermentation broth without control of pH.
J.-Y. Shen et al. / Process Biochemistry 41 (2006) 716–720
719
3.4. Performance on glutamine recovery and salt removal
Fig. 4. Time profile of electrodialytic desalination process of the fermentation broth with control of pH.
of the electrodialytic process, the quantity of SO42 fell quickly. After 150 min, SO42 removal ratio reached 90% and the velocity of removal slowed down. The quantity of glutamine decreased slowly at the beginning of desalination. pH of the broth would fall because OH was easier to transport than SO42. When pH fell to about 2 which was far away from the isoelectric point of glutamine (pI: 5.65), glutamine would be combined with H+ and became cationic state according to the theory of Handerson– Hasselbalch [6]. The quantity of glutamine decreased rapidly with the migration of cationic state glutamine. In the end, the loss of glutamine was in the proximity of 90%. As a comparison, the electrodialytic desalination of the fermentation broth was carried out under 204 A/m2 current density with pH controlled in the proximity of 5.65 (pI of glutamine) through addition of 20% ammonia solutions. As shown in Fig. 4, when the removal ratio of SO42 reached 95%, the loss of glutamine was below 20%, which was far lower than the result without a pH control. Most of the ammonium sulfate would be removed and the glutamine recovery could still hold at a high value when the pH of the fermentation broth was controlled in the proximity of the isoelectic point of glutamine during the electrodialytic process. The shift of maximum 0.5 pH unit from the isoelectric point would cause ionization of part of glutamine. However, the shift was inevitable in our experiments because pH was manually controlled just using an off-line mode due to our experimental condition. The solution pH should be controlled more precisely to minimize the glutamine loss for the further desalination.
The initial current was 8.2 A (279 A/m2) when the constant voltage was the maximum voltage of the direct current power supplier (31.1 V). As shown in Table 1, the glutamine recovery was the lowest. The current transfer required considerable amounts of ions in the solution. The ion-lacking state would form on the surface of ion-exchange membrane when the ion concentration in the fermentation broth could not fulfill the requirement for the ion transfer. At this time, water on the membrane surface would then be ionized into H+ and OH to conduct electricity, and pH varied quickly and would be far away from the isoelectric point of glutamine. Parts of glutamine ionized and lost with the migration process induced by the current density. Therefore, the current density in operation process could not be too high. Under the same conditions, the performance on glutamine recovery and salt removal was also investigated at constant current density (204 or 136 A/m2) as shown in Table 1. The velocity of migration of salt ions in the fermentation broth was slow and it would take a long operation time to get the required concentration of salt ions when the current was 136 A/m2. Glutamine would permeate through the ion-exchange membrane because of concentration gradients. The longer the operation time lasted, the more glutamine lost. Thus, the current density should not be too low. The velocity of migration of salt ions in the fermentation broth would become high when the constant current density was 204 A/m2. The required operation time became shorter and the loss of glutamine reduced. The energy consumption was 1.95 kW h kg1 sulfate under the operation of current density of 204 A/m2 at a current efficiency of 81%. A number of purification steps are required in fermentation process, and the individual yield of each step contributes to the overall yield of the process. New purification technologies and an integrated process would reduce the purification steps and production costs. In this study, the sulfate concentration of the final broth was 3.0 g l1 after the desalination under the operation of constant current density of 204 A/m2. The loss of glutamine (20%) was lower than that after the traditional desalination (30% loss of Gln, data not shown) with ion-exchange resins. The clear solution after the electrodialytic desalination can meet the further simple separation of glutamine from the solution by a process with the anion-exchange resin.
Table 1 Performance of operating conditions of eletrodialysis Operating conditions
Glutamine recovery (%)
Salt removal radio (%)
Desalination time (h)
Current efficiency, h (%)
Specific energy consumption, e (kW h kg1 sulfate)
Constant current density (204 A/m2) Constant current density (136 A/m2) Constant voltage (31.1 V)
78.1 71.7 67.8
95.0 95.0 95.0
5.0 8.1 4.5
81.0 75.1 76.3
1.95 2.18 1.99
720
J.-Y. Shen et al. / Process Biochemistry 41 (2006) 716–720
Acknowledgement Financial support was given by National Key Technologies R&D Program of China (2001BA708B0205 and 2004BA713B09-5).
References [1] Darmaun D, Matthews DE, Bier DM. Glutamine and glutamate kinetic in humans. Am J Physiol 1986;251:117–26. [2] Boza J, Turini M. Effect of glutamine supplementation of the diet on tissue protein synthesis rate of glucocorticoid-treated rats. J Nutr 2001;17:35–40. [3] Calder PC. More good news about glutamine. J Nutr 2000;16:71–3. [4] Isao K. Industrial production of L-glutamine. J Nutr 2001;131:2552–5.
[5] Miyazawa M, Kaneko T, Kaneko T, Yarita K. Method for purifying Lglutamine. US patent 1990; 4:966–99. [6] Stryer L. Biochemistry, 4th ed., New York: W.H. Freeman and Company, 1995. [7] Kazuhisa S, Tetsuya S, Toshikuni Y, Teiriki T. The desalination of a mixed solution of an amino acid and an inorganic salt by means of eletrodialysis with charge-mosaic membrane. J Membrane Sci 1994;100:209–16. [8] Cauwenberg V, Peels J, Resbeut S, Pourcelly G. Application of electrodialysis within fine chemistry. Sep Purif Technol 2001;22– 23:115–21. [9] Vyas PV, Shah BG, Trivedi GS, Gaur PM, Ray P, Adhikary SK. Separation of inorganic and organic acids from glyoxal by electrodialysis. Desalination 2001;140:47–54. [10] Moresi M, Sappino F. Effect of some operating variables on citrate recovery from model solutions by electrodialysis. Biotechnol Bioeng 1998;59:344–50.
Short communication
Desalination of glutamine fermentation broth by electrodialysis Jin-Yu Shen a,*, Jing-Ran Duan a, Li-Xin Yu a, Xin-Hui Xing a, Ping Xu b,* a b
Department of Chemical Engineering, Tsinghua University, Beijing 100084, PR China State Key Lab of Microbial Technology, Shandong University, Jinan 250100, PR China
Received 15 May 2005; received in revised form 31 July 2005; accepted 2 August 2005
Abstract An electrodialytic process was proposed to achieve an efficient desalination of glutamine (Gln) fermentation broth. Several electrodialytic experiments using different combinations of anion- and cation-exchange membranes were carried out, and a set of satisfactory combination of membranes was selected for the desalination. The effects of operational current density and pH on desalination and glutamine recovery were investigated and discussed. The electrical current efficiency and the energy consumption were also studied. The loss of glutamine could be reduced effectively when the current density was kept at 204 A/m2 and pH was controlled near the isoelectric point of glutamine (pI: 5.65) during the process. The clear solution after this electrodialytic desalination can meet the further simple separation of glutamine from the solution using anion-exchange resin. # 2005 Elsevier Ltd. All rights reserved. Keywords: Electrodialysis; Ion-exchange membrane; Fermentation broth; Glutamine; Desalination; Separation
1. Introduction Glutamine (Gln) is the g-carboxylic amidate of glutamic acid (Glu) and it is the most abundant amino acid in the body [1]. In recent years many researches on medical treatment and health care have shown that glutamine is becoming a very promising drug [2,3] and a healthy food ingredient [4], and its industrialization has considerable perspective. Separation process of glutamine from the fermentation broth is the primary factor, which restricts its production cost. And high concentration of inorganic salt, for example, sulfate in the fermentation broth influences the separation of glutamine greatly. However, high concentration of ammonium sulfate (about 6%) should be used to ferment good production of glutamine in broth. The recovery of glutamine from the fermentation broth is low during the traditional dual-columnar separation process of anion- and cationexchange resins because glutamine tends to transform into glutamic acid on both the high acidic and high alkaline resins [5]. Furthermore, much water is required for the * Corresponding authors. Tel.: +86 10 62788568; fax: +86 10 62770304. E-mail addresses: [email protected] (J.-Y. Shen), [email protected] (P. Xu). 1359-5113/$ – see front matter # 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.procbio.2005.08.001
reactivation and washing of the ion-exchange resin, imposing a big burden on wastewater treatment. In order to solve the above problems, we raised an electrodialytic desalination of glutamine fermentation broth, which was easy to separate glutamine by the following single anionexchange columnar process. It should be a promising process for efficient recovery of glutamine from the fermentation broth to cut down the operational cost.
2. Materials and methods 2.1. Reagents, broth and membranes Standard glutamine (pI: 5.65) and glutamic acid (pI: 3.22) [6] were purchased from Sigma (Purity > 99%). Glutamine fermentation broth by Corynebacterium glutamicum ATCC 13032 was provided by State Key Laboratory of Microbial Technology, Shandong University. The ionexchange membranes used in the experiments were provided by Tokuyama Company of Japan. The types of membranes TH1–TH4 used in the study were AM-1 A0039 (0.13–0.16 mm thickness, strong acidic Na type), AMI
J.-Y. Shen et al. / Process Biochemistry 41 (2006) 716–720
717
(0.16–0.20 mm thickness, strong acidic Na type), CM*C0473 (0.12–0.16 mm thickness, strong alkaline Cl type) and CM-1 C-0683 (0.14–0.18 mm thickness, strong alkaline Cl type), respectively.
following formula:
2.2. Analytical methods
where c, F, i, I, t, V, Z and t were referred to solution concentration (mol l1), Faraday’s constant (96,486 Coulomb mol1), the number of compartments, electrical current (A), time (s), solution volume (l), ionic valence number and duration time, respectively [8]. The specific energy consumption e (kW h kg1 sulfate) was estimated from voltage, current, duration, etc. [9] and calculated by the equation as follows:
Glutamine and glutamic acid were determined by a biosensor (Model 2700, YSI, USA). The sulfate analysis was carried out by an ion chromatography (HIC-6 A, Shimadzu, Japan) [7]. 2.3. Pretreatment of fermentation broth The chemical component of the fermentation broth before the pretreatment was 42.0 g l1 glutamine, 5.5 g l1 glutamic acid, 2.0 g l1 glucose, 0.45 M sulfate and 0.05 M of phosphates, pH 6.0. Through pretreatment of the broth by combination of flocculation and ultrafiltration processes, lots of cells, proteins and amylose were removed. Then the broth was decolored using active carbon. Except for a few of cells, proteins, amyloses, and pigments, the main ingredients of the fermentation broth after the pretreatment were 40.0 g l1 glutamine, 5.0 g l1 glutamic acid, 1.8 g l1 glucose, 0.42 M sulfate and 0.05 M of phosphates, pH 6.0. The fermentation broth after pretreatment was used in the following experiments. 2.4. Experimental The experiments were carried out in the laboratorial electrodialyser consisting of seven compartments with alternating cation- and anion-exchange membranes, which was a self-made apparatus. Each compartment contained a 20 cm 10 cm ion-exchange membrane with an effective area of 98 cm2, and between every two compartments was a 0.8 mm polypropylene double-layered mesh grid partition. The electrical potential was applied between the two electrodes by means of an ac–dc rectifier having a variable current capacity of 0–8.2 A and a variable voltage of 0– 31.1 V. And the operation could be done under a constant voltage or constant current condition. Under the direct current condition, cations (such as NH4+and Na+) would migrate toward the cathode and anions (such as SO42 and Cl) toward the anode. Glutamine would not migrate at its isoelectric point because it was amphoteric electrolyte. Therefore, the concentration of inorganic salts was reduced greatly, whereas glutamine still existed in the initial feed solution. The performance of an electrodialytic process can be evaluated by the so-called current efficiency (h) and the specific energy consumption (e) of a given run. Current efficiency is defined as the overall efficiency of current utilization in transporting salts from the diluent stream to the concentrate stream and is usually expressed as a percentage. In this paper, current efficiency (h) was calculated by the
P DðZcVÞi F h ¼ Ri t 0 IðtÞdt
Rt e¼
0
’ðtÞIðtÞdt Dms
(1)
(2)
where the symbols w and Dms were defined as operating voltage and mass quantity transported, respectively; and the other symbols were as the same as in formula (1) [10].
3. Results and discussion 3.1. Effects of ion-exchange membranes on desalination The experiments were carried out under the uniform conditions except for in various combinations of anion- and cation-exchange membranes. The electrodialysis was performed at a constant current of 6 A, which was equivalent to a current density 204 A/m2. The electrodialytic operation was controlled under pH 5.6 0.5. The desalination with various combinations of ionexchange membranes were shown in Fig. 1. The loss of glutamine for combinations C and D was less (13 and 19%, respectively) than combinations A and B (24 and 33%, respectively) at the same salt removal ratio (95%). The differences in the loss of glutamine might be due to the structures of different ion-exchange membranes. At pH 5.65, glutamine existed mostly as electroneutral dipole ions. Glutamine could penetrate membrane through molecular diffusion because of its concentration gradients between the feed compartment and the salt compartment. Although sulfate removal rates were higher in combinations A and B than in the others, the selectivity of the membranes was poor and the recovery of glutamine was low. The membrane selectivity to inorganic salts in combination C was the best in all combinations. The loss of glutamine for combination C was the least (13%), but the operation time was the longest (393 min). Meanwhile, the operation time for combination D was 279 min and the glutamine loss was 19% at the same salt removal ratio (95%). Combination D was selected for further experiments considering various factors such as operation time and loss of product.
718
J.-Y. Shen et al. / Process Biochemistry 41 (2006) 716–720
Fig. 1. Profile of electrodialytic desalination with various combinations: (A) TH1–TH3; (B) TH1–TH4; (C) TH2–TH3; and (D) TH2–TH4.
3.2. Removal ratio of ammonium sulfate with change of current and voltage Fig. 2 showed that the salt concentration changed and the resistance of the stack increased gradually during the electrodialytic process of the fermentation broth with control of pH (5.6 0.5). Therefore, the voltage was adjusted to keep the constant current density (204 A/m2). The voltage reached the highest value of the direct current power supplier (31.1 V) when the salt removal ratio in fermentation broth was 70%. Later, the current density
Fig. 2. Removal ratio of ammonium sulfate with change of current and voltage.
began to fall. The salt removal ratio in fermentation broth reached nearly 95% when the current density fell to 31 A/ m2. Therefore, the end point of the eletrodialytic desalination could be estimated according to the value of current density. 3.3. Effect of pH on loss of glutamine Electrodialytic desalination was carried out under the 204 A/m2 current density without pH control of the fermentation broth as shown in Fig. 3. At the beginning
Fig. 3. Time profile of electrodialytic desalination process of the fermentation broth without control of pH.
J.-Y. Shen et al. / Process Biochemistry 41 (2006) 716–720
719
3.4. Performance on glutamine recovery and salt removal
Fig. 4. Time profile of electrodialytic desalination process of the fermentation broth with control of pH.
of the electrodialytic process, the quantity of SO42 fell quickly. After 150 min, SO42 removal ratio reached 90% and the velocity of removal slowed down. The quantity of glutamine decreased slowly at the beginning of desalination. pH of the broth would fall because OH was easier to transport than SO42. When pH fell to about 2 which was far away from the isoelectric point of glutamine (pI: 5.65), glutamine would be combined with H+ and became cationic state according to the theory of Handerson– Hasselbalch [6]. The quantity of glutamine decreased rapidly with the migration of cationic state glutamine. In the end, the loss of glutamine was in the proximity of 90%. As a comparison, the electrodialytic desalination of the fermentation broth was carried out under 204 A/m2 current density with pH controlled in the proximity of 5.65 (pI of glutamine) through addition of 20% ammonia solutions. As shown in Fig. 4, when the removal ratio of SO42 reached 95%, the loss of glutamine was below 20%, which was far lower than the result without a pH control. Most of the ammonium sulfate would be removed and the glutamine recovery could still hold at a high value when the pH of the fermentation broth was controlled in the proximity of the isoelectic point of glutamine during the electrodialytic process. The shift of maximum 0.5 pH unit from the isoelectric point would cause ionization of part of glutamine. However, the shift was inevitable in our experiments because pH was manually controlled just using an off-line mode due to our experimental condition. The solution pH should be controlled more precisely to minimize the glutamine loss for the further desalination.
The initial current was 8.2 A (279 A/m2) when the constant voltage was the maximum voltage of the direct current power supplier (31.1 V). As shown in Table 1, the glutamine recovery was the lowest. The current transfer required considerable amounts of ions in the solution. The ion-lacking state would form on the surface of ion-exchange membrane when the ion concentration in the fermentation broth could not fulfill the requirement for the ion transfer. At this time, water on the membrane surface would then be ionized into H+ and OH to conduct electricity, and pH varied quickly and would be far away from the isoelectric point of glutamine. Parts of glutamine ionized and lost with the migration process induced by the current density. Therefore, the current density in operation process could not be too high. Under the same conditions, the performance on glutamine recovery and salt removal was also investigated at constant current density (204 or 136 A/m2) as shown in Table 1. The velocity of migration of salt ions in the fermentation broth was slow and it would take a long operation time to get the required concentration of salt ions when the current was 136 A/m2. Glutamine would permeate through the ion-exchange membrane because of concentration gradients. The longer the operation time lasted, the more glutamine lost. Thus, the current density should not be too low. The velocity of migration of salt ions in the fermentation broth would become high when the constant current density was 204 A/m2. The required operation time became shorter and the loss of glutamine reduced. The energy consumption was 1.95 kW h kg1 sulfate under the operation of current density of 204 A/m2 at a current efficiency of 81%. A number of purification steps are required in fermentation process, and the individual yield of each step contributes to the overall yield of the process. New purification technologies and an integrated process would reduce the purification steps and production costs. In this study, the sulfate concentration of the final broth was 3.0 g l1 after the desalination under the operation of constant current density of 204 A/m2. The loss of glutamine (20%) was lower than that after the traditional desalination (30% loss of Gln, data not shown) with ion-exchange resins. The clear solution after the electrodialytic desalination can meet the further simple separation of glutamine from the solution by a process with the anion-exchange resin.
Table 1 Performance of operating conditions of eletrodialysis Operating conditions
Glutamine recovery (%)
Salt removal radio (%)
Desalination time (h)
Current efficiency, h (%)
Specific energy consumption, e (kW h kg1 sulfate)
Constant current density (204 A/m2) Constant current density (136 A/m2) Constant voltage (31.1 V)
78.1 71.7 67.8
95.0 95.0 95.0
5.0 8.1 4.5
81.0 75.1 76.3
1.95 2.18 1.99
720
J.-Y. Shen et al. / Process Biochemistry 41 (2006) 716–720
Acknowledgement Financial support was given by National Key Technologies R&D Program of China (2001BA708B0205 and 2004BA713B09-5).
References [1] Darmaun D, Matthews DE, Bier DM. Glutamine and glutamate kinetic in humans. Am J Physiol 1986;251:117–26. [2] Boza J, Turini M. Effect of glutamine supplementation of the diet on tissue protein synthesis rate of glucocorticoid-treated rats. J Nutr 2001;17:35–40. [3] Calder PC. More good news about glutamine. J Nutr 2000;16:71–3. [4] Isao K. Industrial production of L-glutamine. J Nutr 2001;131:2552–5.
[5] Miyazawa M, Kaneko T, Kaneko T, Yarita K. Method for purifying Lglutamine. US patent 1990; 4:966–99. [6] Stryer L. Biochemistry, 4th ed., New York: W.H. Freeman and Company, 1995. [7] Kazuhisa S, Tetsuya S, Toshikuni Y, Teiriki T. The desalination of a mixed solution of an amino acid and an inorganic salt by means of eletrodialysis with charge-mosaic membrane. J Membrane Sci 1994;100:209–16. [8] Cauwenberg V, Peels J, Resbeut S, Pourcelly G. Application of electrodialysis within fine chemistry. Sep Purif Technol 2001;22– 23:115–21. [9] Vyas PV, Shah BG, Trivedi GS, Gaur PM, Ray P, Adhikary SK. Separation of inorganic and organic acids from glyoxal by electrodialysis. Desalination 2001;140:47–54. [10] Moresi M, Sappino F. Effect of some operating variables on citrate recovery from model solutions by electrodialysis. Biotechnol Bioeng 1998;59:344–50.