AMMONIA STRIPPING DEVICE, AND RESOURCE RECOVERY TYPE HIGH CONCENTRATION WASTEWATER TREATMENT SYSTEM USING THE SAME

Abstract

Provided is an ammonia stripping device, and a resource recovery type high concentration wastewater treatment system using the ammonia stripping device. The ammonia stripping device optimizes the conditions of pH, temperature, and pressure within a decompression type reactor with respect to raw water resulting from gathering high concentration wastewater and removing a solid therefrom and causes the stripped ammonia to be highly purified in a gas phase without phase change by a separation membrane process of causing the stripped ammonia to pass through a gas separation membrane, and selectively recovering the recovered ammonia. The recovered ammonia of high purity can be reused in being made into resources such as production of urea solutions, power generation by raw materials of green hydrogen and mixed fuel, and so on.

Claims

1. A resource recovery type high concentration wastewater treatment method comprising: an ammonia stripping process performed by a decompression type reactor (10) under a condition of controlled pressure with respect to raw water flowing in after pretreatment from high concentration wastewater, wherein the pressure of the decompression type reactor (10) is controlled to be 0.5 to 2 bar, thereby carrying out consecutive operations, wherein ammonia introduced from the decompression type reactor (10) passes through a heat exchanger (20) having a heat-radiating path, a cooler (50) supplies water to the heat-radiating path to maintain a fixed temperature of the heat exchanger (20), and the ammonia passes through a trap (30) where water condensed from the heat exchanger (20) is recovered, and the ammonia moves to a stripped ammonia gas collector (60) which recovers ammonia that has passed through the trap (30), a separation membrane process of causing an ammonia mixed gas recovered by the stripping process to pass through a polymeric gas separation membrane, and the ammonia gas selectively permeated through the polymeric gas membrane without phase change is recovered in high purity after passing through pressure adjustment, flow measurement and ingredients analysis steps, a resource recovery process of the recovered high purity ammonia.

2. The resource recovery type high concentration wastewater treatment method according to claim 1, wherein the raw water having a pH of 8.8 to 11.

3. (canceled)

4. The resource recovery type high concentration wastewater treatment method according to claim 1, wherein under the condition of the pressure of the decompression type reactor, the operations are carried out under the condition of a temperature of 35 C. to 60 C.

5. The resource recovery type high concentration wastewater treatment method according to claim 1, wherein the decompression type reactor has an ultrasonic generator attached thereto.

6. (canceled)

7. The resource recovery type high concentration wastewater treatment method according to claim 1, wherein the polymeric gas separation membrane is made of a perfluorinated sulfonic acid polymer or a polyimide-based (polyamide-imides and co-polyimide) polymer.

8. The resource recovery type high concentration wastewater treatment method according to claim 6, wherein the polymeric gas separation membrane is a hollow fiber membrane composed of a polyimide-based (polyamide-imides and co-polyimide) polymer having a dense structure on the surface of the membrane and a finger structure formed by rapid solvent escape on the inside.

9. The resource recovery type high concentration wastewater treatment method according to claim 7, wherein the hollow fiber membrane is thermally stable by chemical crosslinking.

10. (canceled)

11. The resource recovery type high concentration wastewater treatment method according to claim 1, wherein the ammonia mixed gas recovered by the stripping process flows into the polymeric gas separation membrane through the pressure control step, and gas remaining behind passing through the polymeric gas separation membrane is disused by passing a pressure measurement step, a back pressure regulation step, and a flow measurement step.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] FIG. 1 is a schematic diagram showing an ammonia stripping device according to the present invention,

[0046] FIG. 2 illustrates the process flow of a resource recovery type high concentration wastewater treatment system according to the present invention,

[0047] FIG. 3 illustrates physical properties of the main gas to be separated in the resource recovery type high concentration wastewater treatment system according to the present invention,

[0048] FIG. 4 is a photograph by a scanning electron microscope (SEM) from polymeric gas separation membrane used in a separation membrane process of the resource recovery type high concentration wastewater treatment system according to the present invention,

[0049] FIG. 5 illustrates a membrane module process for a polyimide hollow fiber membrane shown in FIG. 4,

[0050] FIG. 6 shows a result of thermal analysis before and after crosslinking of the membrane modified by a chemical crosslinking reaction to the polyimide hollow fiber membrane of FIG. 5, and

[0051] FIG. 7 is a flow chart of the separation membrane process with respect to the resource recovery type high concentration wastewater treatment system according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0052] Hereinafter, the present invention is described in detail.

[0053] FIG. 1, which is a schematic diagram showing an ammonia stripping device according to the present invention, provides the ammonia stripping device comprising: a decompression type reactor 10 configured to carry out an ammonia stripping process under a condition that the pressure of raw water obtained after pretreatment from high concentration wastewater is controlled; a heat exchanger 20 configured to cause ammonia flowing in from the decompression type reactor to pass through a heat-radiating path; a cooler 50 configured to supply water to the heat-radiating path to maintain a fixed temperature of the heat exchanger; a trap 30 configured to recover water condensed from the heat exchanger; and a stripped gas collector 60 configured to recover ammonia passing through the trap.

[0054] The high concentration wastewater according to the present invention is any one selected from a group consisting of: anaerobic digestion outflow water of sewage sludge; an anaerobic digestive fluid of sewage sludge; livestock night soils in slurry type comprising pig liquid or cattle slurry; a digestive liquid of livestock night soils; and a codigestion supernatant of swine manure and food, and raw water resulting from gathering the wastewater and removing a solid therefrom is used. At this time, since it is meant that as the concentration of ammonia in the solid increases gradually, the concentration of recoverable ammonia is rich, according to an exemplary embodiment of the present invention, each concentration of 3,500 mg/L of TN, 2,500 mg/L of NH.sub.4.sup.+N, 300 mg/L of TP, 100 mg/L of PO.sub.4.sup.3P is limited and described, but should not be construed as being limited thereto.

[0055] Also, with respect to the ammonia stripping process using the decompression type reactor, in case that pH is uniformly maintained during a decompression stripping process, reaction time required for stripping decreases more and more, or the final concentration of ammonia may be maintained to be lower. At this time, it is preferable that the pH during the stripping process using decompression ranges from 8.8 to 11, and in order to maintain high concentration, the concentration may be adjusted in such a manner as to additionally put any one basic material selected from a group consisting of NaOH, CaO, and Ca(OH).sub.2.

[0056] The conventional ammonia stripping method is to remove an ammonium ion (NH.sub.4.sup.+) in the state of gas by converting it to ammonia (NH.sub.3) under the condition that pHs of wastewater are more than 11, and at this time, in order to raise the pHs, calcium hydroxide and sodium hydroxide are mainly used, and a method of simultaneously removing phosphorous ingredients is used through the condensation and precipitation of phosphorus. However, although the conventional ammonia stripping method is advantageous in that a recovery rate of nitrogen is high because ammonia is removed in such a manner as to perform stripping after causing most of the ammonia to exist in a gaseous state by setting up the condition of high pHs, it is problematic in that there is a necessity for performing air-blowing for a long time in order to make excessively saturated ammonia discharged in the air, a high temperature and a high pH condition are required, and a chemical material intended for making pH maintained is required in an excess of quantity.

[0057] On the contrary, the ammonia stripping device using the decompression type reactor according to the present invention carries out consecutive operations under a fixed condition of decompression with respect to the raw water flowing in, so an ammonia stripping phenomenon and a decrease in pH scale may be confirmed.

[0058] At this time, with respect to an execution condition required for the decompression type reactor according to the present invention, because of having an effect on ammonia stripping according to each condition of changes in pH, temperature, and pressure is secured, the pH, temperature, and pressure conditions are optimized, so the decompression type reactor may be driven at low energy.

[0059] With respect to the preferable decompression condition, decompression is performed under a condition of 0.5 bar to 2 bar, and according to another exemplary embodiment of the present invention, the result of occurrence of the ammonia stripping phenomenon and a decrease in pH scale is presented under the fixed condition of 1 bar, but the condition of pressure is not limited to that shown in this exemplary embodiment.

[0060] Also, under the pressure condition, pH ranges from 8.8 to 11, and more preferably, in case that decompression is performed under the condition that pH ranges from 9.5 to 10, may be confirmed a result which shows that the reaction time decreases, and the concentration of ammonia reduces as well up to a 90% to 95% level in comparison with its early concentration of 2,500 mg/L. Currently, when the condition of pH shows that pHs exceed 11, the reaction time reduces according to an increase in pH scale, but the effect of a rise in efficiency of ammonia removal is insignificant, so the condition is inefficient in comparison with expenses for maintaining high pH.

[0061] Also, a preferable condition of temperature is 35 C. to 60 C., and more preferably, 35 C. to 50 C. Although the efficiency of ammonia removal increases as the temperature increases gradually, when the temperature exceeds 60 C., the effect of a rise in efficiency of ammonia removal is insignificant in comparison with expenses required for raising the temperature of the reactor.

[0062] In order to enhance the efficiency of ammonia stripping, the ammonia stripping device according to the present invention may carry out vacuum stripping and ultrasonic stripping together as an ultrasonic generator is attached into the decompression type reactor.

[0063] When an ultrasonic wave is emitted, by electrical oscillation, to the raw water flowing in after pretreatment from the high concentration wastewater, the moment it decreases from high tension to low tension, bubbles occur, and upon a decrease in tension to low tension, the bubbles grow, and when the bubbles are formed and grow, ammonia gas is included into the bubbles. Since the bubbles instantaneously occurring in large quantities due to this electrical oscillation of the ultrasonic wave are removed using a vacuum stripping device, the efficiency of stripping may be improved.

[0064] Since 20 kHz or more of a sound wave is generated from the ultrasonic generator so that a stripping process is carried out by mechanical vibration, efficiency of the vacuum stripping device may increase.

[0065] FIG. 2, which illustrates the process flow of a resource recovery type high concentration wastewater treatment system according to the present invention, provides the resource recovery type high concentration wastewater treatment system which performs: an ammonia stripping process of performing vacuum stripping, or vacuum and ultrasonic stripping together with respect to raw water resulting from gathering high concentration wastewater and removing a solid therefrom; a separation membrane process of causing the stripped-down ammonia to pass through polymeric gas separation membrane; and a process of making the ammonia of high concentration selectively recovered by the separation member process into resources.

[0066] The resource recovery type high concentration wastewater treatment system according to the present invention may carry out a pretreatment process, such as screening, condensation and/or precipitation, aerated grit, floating, electrolysis, etc. after gathering high concentration wastewater and removing a solid therefrom, and a well-known process required for pretreatment may be applied.

[0067] After said pretreatment, the resource recovery type high concentration wastewater treatment system according to the present invention carries out the ammonia stripping process of removing ammonia from the raw water using the decompression type reactor.

[0068] The conventional ammonia stripping method is to remove an ammonium ion (NH.sub.4.sup.+) in the state of gas by converting it to ammonia (NH.sub.3) under the condition that pHs of wastewater are more than 11, and at this time, in order to raise the pHs, calcium hydroxide and sodium hydroxide are mainly used, and a method of simultaneously removing phosphorous ingredients is used through the condensation and precipitation of phosphorus. However, although the conventional ammonia stripping method is advantageous in that a recovery rate of nitrogen is high because ammonia is removed in such a manner as to perform stripping after causing most of the ammonia to exist in a gaseous state by setting up the condition of high pHs, it is problematic in that there is a necessity for performing air-blowing for a long time in order to make excessively saturated ammonia discharged in the air, a high temperature and a high pH condition are required, and a chemical material intended for making pH maintained is required in an excess of quantity.

[0069] On the contrary, the ammonia stripping device using the decompression type reactor according to the present invention carries out consecutive operations under a fixed condition of decompression with respect to the raw water flowing in, so an ammonia stripping phenomenon and a decrease in pH scale may be confirmed.

[0070] On the contrary, the ammonia stripping device using the decompression type reactor according to the present invention carries out consecutive operations under a fixed condition of decompression with respect to raw water flowing in, so an ammonia stripping phenomenon and a decrease in pH scale may be confirmed.

[0071] Also, since the ultrasonic generator is attached into the decompression type reactor from any location within the decompression type reactor, vacuum stripping and ultrasonic stripping are carried out together, so the efficiency of stripping can enhance.

[0072] The resource recovery type high concentration wastewater treatment system according to the present invention carries out the separation membrane process of causing the ammonia mixed gas recovered by the stripping process to pass through the polymeric gas separation membrane.

[0073] The polymeric gas separation membrane is a nonporous, high polymer membrane through which gas penetrates in such a manner as to cause the gas to be soluble from the surface of a polymer and to diffuse through free volume, and currently, gas permeability is calculated in such a manner as to multiply a solubility value by a diffusion coefficient according to a solution-diffusion model.

[0074] Referring to FIG. 3, which illustrates the physical properties of the main gases to be separated in the resource recovery type high concentration wastewater treatment system according to the present invention, it is expected that permeation selectivity will be high because a difference in solubility and a difference in molecular size (diffusivity) are large in case of NH.sub.3/O.sub.2 and NH.sub.3/N.sub.2. Accordingly, the polymeric gas separation membrane according to the present invention is a high permeation selectivity separation membrane showing excellent selectivity aimed for the mixed gas of NH.sub.3/N.sub.2.

[0075] The highly polymerized separation membrane having a separation property with respect to NH.sub.3/O.sub.2 or NH.sub.3/N.sub.2 (occupying the greatest specific gravity), NH.sub.3/CO.sub.2 (showing a small difference in solubility), and NH.sub.3/He or NH.sub.3/H.sub.2 (showing a small difference in diffusivity) is selected in consideration of the solubility of a solvent, workability, the easiness of synthesis, and so on, and it is preferable that a perfluorinated sulfonic acid polymer material, or a polyimide-based (polyamide-imides and co-polyimide) polymer material is used.

[0076] The perfluorinated sulfonic acid polymer has stability physically and/or chemically because a main chain is fluorinated and has high NH.sub.3 permeability thanks to high affinity of a sulfonic acid group of a side chain, and NH.sub.3.

[0077] Also, the polyimide-based (polyamide-imides and co-polyimide) polymer is advantageous in that a chemically resistant property is high, a heat-resisting property, is excellent, and a possibility to induce various types of chemical structure, and the possibility of reforming is high.

[0078] FIG. 4 shows, as a preferable exemplary embodiment of the highly polymerized separation membrane used in the separation membrane process of the resource recovery type high concentration wastewater treatment system according to the present invention, a photograph result captured by a scanning electron microscope (SEM) concerning the section and thickness of a polyimide hollow fiber membrane, wherein the hollow fiber membrane has an external diameter of 400 m to 500 m, and a membrane thickness of 70 m to 100 m.

[0079] As the thickness of the separation membrane material gets thin as a thin film, ammonia permeability may be maximized.

[0080] Also, the polymeric gas separation membrane is able to be applied into a flat membrane or a hollow fiber membrane and is provided in a membrane module consisting of the flat membrane or the hollow fiber membrane.

[0081] FIG. 5 illustrates a process for the membrane module of the polyimide hollow fiber membrane shown in FIG. 4, the membrane is produced in the form of the hollow fiber membrane and is then modulated and used in a tube type, so the module of the hollow fiber membrane may have an effective area per unit volume in comparison with flat membrane type-modules, and are more preferable because a process combination and the easiness of operation are excellent.

[0082] Also, with respect to the polyimide hollow fiber membrane having thermal stability at temperature ranges which reach 200 C. so as to resist severe circumstances until reaching the process of recovering high concentration, as a result of performing a dry process after crosslinking by soaking it in a crosslinking agent (p-xylenediamine) for 10 minutes, since remarkable thermal stability was confirmed, performance of the membrane may be improved by a stable crosslinking reaction.

[0083] FIG. 6 shows a result of thermal analysis before and after crosslinking of the membrane modified by a chemical crosslinking reaction with respect to the polyimide hollow fiber membrane, and thermal stability compared with that shown before crosslinking may be confirmed.

[0084] FIG. 7, which is a flow chart of the separation membrane process with respect to the resource recovery type high concentration wastewater treatment system according to the present invention, represents that the ammonia mixed gas recovered by the stripping process flows into the polymeric gas separation membrane through a step of controlling pressure, and the ammonia gas which selectively permeates through the polymeric gas membrane is recovered in a state of high purity by passing a step of analyzing ingredients after pressure adjustment and flow measurement steps.

[0085] Also, the ammonia mixed gas recovered by the stripping process flows into the polymeric gas separation membrane through a pressure control step, and gas remaining after passing through the highly gas separation membrane is disused by-passing pressure measurement, back pressure regulator (BPR), and flow measurement steps, and it is characteristic in that the gas is treated by an ammonia neutralization step just before its disuse.

[0086] With respect to the process of making the recovered ammonia into resources, which is carried out by the resource recovery type high concentration wastewater treatment system according to the present invention, the ammonia recovered by being made to highly purify selectively through the ammonia stripping process in low electric power and the separation membrane process of causing the ammonia-mixed to pass through the highly polymerized separation membrane as described above may be reused in the production of urea solutions, the raw materials of green hydrogen, power generation by ammonia-mixed fuel of coal-fired electrical power plants, and so on.

[0087] Hereinafter, the present invention is described in more detail with reference to examples.

[0088] These examples are intended for more specifically describing the present invention and should not be construed as limiting the scope of the present invention thereto.

1. Evaluation on Ammonia Stripping Process Using Decompression Type Reactor

Example 1

[0089] 2 L of a specimen, anaerobic digestion outflow water of sewage sludge, gathered from a water regeneration center was prepared, and according to a process test method, the specimen was analyzed as showing that the concentration of TN was 7,800 to 10,700 mg/L, and the concentration of ammonia was 1,700 to 9,600 mg/L.

[0090] With respect to effluent to be stripped down, the early concentration of NH.sub.3 was adjusted to 2,500 mg/L, and a decompression type reactor was used and operated under the condition that pH was set up to be 9.5 and temperature was set up to be 35 C. and 50 C. At this time, the operation was carried out in the state of a condition of decompression being fixed to the condition that gauge pressure was 1.0 bar.

[0091] A result of the concentration of NH.sub.3N and a change rate shown at each temperature depending on decompression time under the condition of a pH of 9.5 was described in Table 1 below. However, the following result was based on the fact that after the early pH was fixed to be 9.5, a decline in pH resulting from stripping wasn't adjusted artificially.

TABLE-US-00001 TABLE 1 Result of Operation of Decompression Type Reactor under Condition of pH of 9.5 (Pressure Being Fixed to 1 bar) pH of 9.5 Decompression NH.sub.3N C.sub.1/C.sub.0 Time (min) 35 C. 50 C. 35 C. 50 C. 0 2,620 3,260 1.00 1.00 60 1,600 1,440 0.61 0.44 180 1,200 840 0.46 0.26 240 920 496 0.35 0.15 300 712 528 0.27 0.16

[0092] As the result of an experiment of the decompression type reactor under the condition that the pH was 9.5, in order to lead to a more than 50% decrease in comparison with the early concentration of ammonia, in case of 35 C., it took about 170 minutes, in case of 50 C., it took about 100 minutes, and the final concentration of ammonia within the decompression type reactor reduced up to about 73% and about 84% in comparison with its early concentration under the condition of each temperature of 35 C. and 50 C. when 300 minutes passed after the operation. That is, the high efficiency of ammonia stripping showed at 50 C.

[0093] Since the experimental values resulted from the fact that after the early pH was fixed to be 9.5, a decline in pH depending on stripping wasn't adjusted artificially, in case that pH is maintained uniformly during the stripping process using decompression, reaction time for stripping will be able to decrease, or the final concentration of ammonia will be able to be maintained to be lower.

Example 2

[0094] An experiment was carried out in the same manner as that shown in said Example 1 except the fact that a condition was changed to the condition of a pH of 10, and a result of the concentration of NH.sub.3N and a change rate shown at each temperature depending on decompression time under the condition of the pH of 10 was described in Table 2 below.

TABLE-US-00002 TABLE 2 Result of Operation of Decompression Type-Reactor under Condition of pH of 10 (Pressure Being Fixed to 1 bar) pH of 10 Decompression NH.sub.3N C.sub.1/C.sub.0 Time (min) 35 C. 50 C. 35 C. 50 C. 0 2,550 2,800 1.00 1.00 60 1,580 1,320 0.62 0.47 180 750 700 0.29 0.25 240 296 188 0.12 0.07 300 156 74 0.06 0.03

[0095] As confirmed through Table 2 above, in case that the pH was 10, in order to lead to a more than 50% decrease in comparison with the early concentration of ammonia, under the temperature condition of 35 C., it took about 75 minutes, and under the temperature condition of 50 C., it took about 60 minutes, and under the condition of each temperature when 300 minutes passed after the operation, the final concentration of ammonia within the decompression type reactor reduced up to about 94% (at 35 C.) and about 97% (50 C.) in comparison with its early concentration. Through a stripping test performed under the condition of the pH of 10, the excellent efficiency of stripping was also confirmed under the temperature condition of 50 C.

[0096] As confirmed through Table 2 above, in spite of the fact that no pH was artificially adjusted during the reaction time under the condition of the pH of 10, was confirmed the result in which the final concentration of the ammonia was 156 mg/L and 74 mg/L under the condition of each temperature of 35 C. and 50 C., thereby reducing up to about 94% and about 97% in comparison with its early concentration.

Example 3

[0097] An experiment was carried out in the same manner as that shown in said Example 1 except the fact that a condition was changed to the condition of a pH of 11.5, and a result of the concentration of NH.sub.3N and a change rate shown at each temperature depending on decompression time under the condition of the pH of 11.5 was described in Table 3 below.

TABLE-US-00003 TABLE 3 Result of Operation of Decompression Type-Reactor under Condition of pH of 11.5 (Pressure Being Fixed to 1 bar) pH of 11.5 Decompression NH.sub.3N C.sub.1/C.sub.0 Time (min) 35 C. 50 C. 35 C. 50 C. 0 2,340 2,250 1.00 1.00 60 1,490 1,350 0.64 0.60 180 730 510 0.31 0.23 240 500 300 0.21 0.13 300 310 125 0.13 0.06 360 160 85 0.07 0.04

[0098] As confirmed through Table 3 above, in case that the pH was 11.5, in order to lead to a more than 50% decrease in comparison with the early concentration of ammonia, under the condition of the temperature of 35 C., it took about 100 minutes, and under the condition of the temperature of 50 C., it took about 75 minutes, and under each temperature condition when 360 minutes passed after the operation, the final concentration of the ammonia within the decompression type reactor reduced up to about 93% (at 35 C.), and 96% (at 50 C.) in comparison with its early concentration.

[0099] That is, unlike the results shown under the conditions of each pH of 9.5 and 10, since ammonia stripping efficiencies resulting from each temperature were accomplished to be similar to each other, in case of the pH of more than 10.0, it was confirmed that the effect of a decrease in reaction time or a rise in removal efficiency resulting from an increase in pH was insignificant.

[0100] Also, under the condition of the pH of more than 10, after the reaction time of 300 minutes passed, the concentration of ammonia reduced up to a 90% to 95% level in comparison with its early concentration of 2,500 mg/L.

[0101] Based on this result of the experiment, since it was confirmed that the ammonia concentration reduced in spite of the fact that after each early pH was set up to be 9.5, 10, and 11.5, no additional chemicals for maintaining the fixed pHs were put during the reaction time, if the fixed pH conditions are maintained, the reaction time and the final ammonia concentration will be able to reduce.

[0102] However, after an amount of ammonia intended for recovery is set up, under temperature and/or time conditions, since the concentration of ammonia gas can reduce, there will be no need to put chemicals for maintaining the fixed pHs, and this is useful to low energy and the recovery of resources for a decrease in greenhouse gas emissions.

<Experimental Example 1> Evaluation on Factor of Operation of Decompression Type Reactor

[0103] The concentration of ammonia and the efficiency of ammonia removal depending on each pH and temperature within the decompression type reactor were measured and described as shown in Table 4 below, and a result according to each condition of decompression was described in Table 5 below.

TABLE-US-00004 TABLE 4 Evaluation on Ammonia Concentration and Efficiency of Ammonia Removal According to Each pH and Temperature Concentration and Removal Efficiency of Ammonia Condition of Experiment pH of 9.5 pH of 10 pH of 10.5 pH of 11 Temperature 3,750 3,550 3,110 2,880 2,760 () (6%) (17%) (23%) (27%) 25 C. 3,340 3,200 3,140 2,830 2,460 (3%) (15%) (16%) (25%) (35%) 50 C. 2,820 2,680 2,130 1,680 1,330 (25%) (29%) (43%) (55%) (65%) 80 C. 2,710 2,670 1,950 1,360 800 (28%) (34%) (48%) (64%) (79%)

TABLE-US-00005 TABLE 5 Evaluation on Ammonia Concentration and Efficiency of Ammonia Removal according to Each Condition of Decompression Condition of Removal Rate of No. Experiment pH Temperature Ammonia (%) 1 Operation Stop of 9.5 35 16 2 Pump 10 35 5 3 10.3 35 17 4 10.7 35 29 5 Consecutive 9.5 20 12 6 Operations of 10 20 17 7 Pump 11.5 20 14 8 9.5 35 64

[0104] As confirmed through Table 5 above, as the result of an experiment concerning the operation stop of a pump, it was confirmed that the removal of the ammonia didn't reach even a 30% removal rate, whereas upon consecutive operations of the pump, the removal of the ammonia reached a 64% removal rate at its maximum. In the cases of No. 5 and No. 8, as the result, it was confirmed that even under the same conditions of pHs, the ammonia removal rates were largely affected by each temperature.

2. Evaluation on Separation Membrane Process Using Polymeric Gas Separation Membrane

<Example 4> Production of Polyimide Hollow Fiber Membrane

[0105] A dope solution was produced at a weight rate of 27 to 73 with a polyimide blend (Torlon, P84) and a solvent of NMP, and a hollow fiber membrane was produced using a phase transition phenomenon by a dry and/or wet method including a process of carrying out emission through a nozzle, and a phase separation at a coagulation bath. Washing and drying the solvent in a winding machine were performed, so modulation was performed.

<Experimental Example 2> Morphology of Polymeric Gas Separation Membrane

[0106] To observe structural characteristics of the polyimide hollow fiber membrane produced as mentioned above, photographing of its section using a scanning electron microscope (SEM) was performed, and the photograph was illustrated in FIG. 4. As a result thereof, it was confirmed that the external diameter and the internal diameter of the hollow fiber membrane were about 550 m and about 400 m, respectively, thickness of the membrane was about 70 m to 80 m. Also, as a result of observing the section of the separation membrane in 2,000 magnifications, a surface of the membrane had very thin and dense structure (a selective layer), and from the inside thereof, was observed finger structure formed when the solvent rapidly slipped out of the inside, so it was confirmed that the hollow fiber membrane was well produced.

<Experimental Example 3> Evaluation on Permeation Performance of Module of Polymeric Gas Separation Membrane

[0107] In order to confirm separation performance of the gas separation membrane using a mixed gas of NH.sub.3/N.sub.2, the polyimide hollow fiber membrane produced as described above was modulated as presented in FIG. 5, a nafion hollow fiber membrane was modulated in such a manner as to gather several strands by one bundle, and thus each module of the hollow fiber membranes was composed of 34 cm effective long20 strands, and 17 cm effective long53 strands in a inch seamless (SUS) tube.

[0108] Mixing gases used in a separation test for a mixed gas of NH.sub.3/N.sub.2 was ordered and used according to each concentration (mol % NH.sub.3/mol % N.sub.2 represents 10/90, 30/70, 50/50, 70/30, and 88/12).

[0109] Each pressure of the supply gases was adjusted by a regulator installed in a gas cylinder, and a permeable cell including the separation membrane was installed in a temperature chamber, so an operation temperature was regulated. A flow was adjusted by a mass flow controller (MFC), pressure shown from a retention side was adjusted by a back pressure regulator (BPR) to be maintained in the same manner as supply pressure, and gas which permeates through the separation membrane was sent for gas chromatography (GC) through a mass flow meter (MFM), so the flow and composition were analyzed. As a result, thereof, the result of use of the polyimide hollow fiber membrane was described in Table 6 below, and the result shown from the module of the nafion hollow fiber membrane was described in Table 7 below.

TABLE-US-00006 TABLE 6 Result of Ammonia Recovery Using Module of Polyimide Hollow Fiber Membrane Condition of Operation Result Supply Permeation Factor Supply Permeation Composition Supply Composition Permeation of Temp. Pressure Pressure NH.sub.3 N.sub.2 Flow NH.sub.3 Flow Separation ( C.) (bar) (bar) (mol %) (mol %) ml/min (mol %) ml/min 25 6 1 10 90 100 63.3 3.4 15.5 4 1 50 50 50 95.8 15.9 22.7 4 1 50 50 200 99.0 80.9 99.0

TABLE-US-00007 TABLE 7 Result of Ammonia Separation Using Module of Nafion Hollow Fiber Membrane Condition of Operation Result Supply Permeation Recovery Supply Permeation Composition Supply Composition Permeation Rate Temp. Pressure Pressure NH.sub.3 N.sub.2 Flow NH.sub.3 Flow of NH.sub.3 ( C.) (bar) (bar) (mol %) (mol %) ml/min (mol %) ml/min % 25 6 1 10 90 100 84.4 3.8 31.7 4 1 30 70 99.0 22.5 74.1 4 1 50 50 99.3 40.9 81.3 3 1 70 50 99.7 61.7 88.0

[0110] Based on each result shown in Table 6 and Table 7 above, in case that each concentration of the ammonia contained in the mixing gases supplied was supplied to be 30 mol % or more, it was confirmed that each concentration of the ammonia which permeates through the polymeric gas membrane was 95 mol % or more, more preferably, 99 mol % or more, so its recovery was realized.

[0111] Also, since the flow rate resulting from permeation increased largely compared with the range of an increase in ammonia concentration of each supply gas, a recovery rate of the ammonia increased.

<Experimental Example 4> Evaluation on Stability of Module of Polymeric Gas Separation Membrane

[0112] To evaluate thermal stability of the polyimide hollow fiber membrane, thermogravimetric (TGA) analysis was carried out, and in FIG. 6, was illustrated a result of the analysis on heat shown before and after crosslinking of the membrane modified by a chemical crosslinking reaction with respect to the polyimide hollow fiber membrane.

[0113] As its result, since it was confirmed that the polyimide hollow fiber membrane had thermal stability at temperature ranges which reached 200 C., whereas after crosslinking, it had thermal stability at temperature ranges which reached about 600 C., it was confirmed that performance of the membrane could be improved by the stable crosslinking reaction.

[0114] As previously described, although the present invention has been described in detail based on only the detailed exemplary embodiments and examples mentioned, it will be apparent to those having ordinary skill in the art that modifications and alternations can variously be made within the technical idea and the scope of the present invention, and it is to be natural that these modifications and alternations falls with the scope of the accompanying claims.