JP2014184354A - Processing system of ink discharge water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize water processing system in which ink discharge water is efficiently decolorated, clarified, and can be recycled as intermediate water.SOLUTION: In a processing system, ink discharge water including a pigment is processed to generate intermediate water. The processing system includes a first treatment part 10 in which microfiltration is performed; and a second treatment part 30 in which filtration water is made to contact with ozone. The first treatment part 10 includes: a storage tank 11; a microfiltration unit 12 that is slightly smaller than the storage tank 11; a water sending path 19 in which the filtration water is sent to the second treatment part 30; and a suction pump 20 in which a downstream of the microfiltration unit 12 is decompressed. The concentrated ink discharge water is intermittently drained from the storage tank 11.

Description

  The present invention relates to a water treatment system that purifies ink wastewater containing pigments and enables reuse as intermediate water.

  In the field of the printing industry, water-soluble inks are frequently used in flexographic printing and the like. Water-soluble ink has an advantage that it is easy to handle because it has no residual organic solvent.

  The water-soluble ink generally contains a pigment that is a coloring component such as carbon black, a water-soluble resin, and an additive. A pigment that is not soluble in water is contained in the water-soluble ink in a state of being dispersed in water. Some water-soluble inks contain dyes that dissolve in water.

  In a printing factory where printing is performed using water-soluble ink, pipes and the like are washed with water when the ink is switched, and thus a large amount of colored waste water (ink waste water) is generated.

  Prior art relating to such ink wastewater treatment is disclosed in, for example, Patent Document 1 and Patent Document 2.

  Patent Document 1 discloses a treatment method for decolorizing and purifying to a level that can be reused as intermediate water by performing ozone treatment after biological treatment. In order to increase the efficiency of biological treatment, it has also been proposed to separate the pigment using a microfiltration membrane before biological treatment.

  Patent Document 2 discloses a wastewater treatment method that performs membrane separation treatment with a microfiltration membrane or the like on wastewater whose solid content is within a certain range, and discharges the obtained treated water to a river or the like. .

Japanese Patent Laying-Open No. 2005-169304 JP 2006-181549 A

  Since the microfiltration membrane is designed with high accuracy in the pore size distribution in the range of about 0.1 μm to 10 μm, it is effective for separating fine pigments whose particle size distribution is relatively stable.

  However, when ink wastewater discharged in large quantities is pressurized with a pump or the like and filtered with a microfiltration membrane, the pigment is clogged in the microfiltration membrane, and the microfiltration membrane is likely to be replaced frequently. Since the microfiltration membrane is expensive, if the replacement frequency is increased, the running cost is high for use in wastewater treatment, and practical application is difficult.

  Accordingly, an object of the present invention is to provide a practical treatment system that can efficiently decolorize and purify ink waste water and reuse it as intermediate water.

  The present invention is a processing system that generates treated water that can be used as at least intermediate water by treating ink wastewater containing pigments. The 1st process part which carries out precision filtration of the ink waste water, and the 2nd process part which makes the filtered water processed by the 1st process part contact ozone.

  The first processing unit has a storage tank that receives ink waste water, an outer method that is slightly smaller than the inner method of the storage tank, and is connected to the microfiltration unit that is housed in the storage tank and the microfiltration unit And a water supply path for sending filtered water to the second processing unit, and a suction pump for depressurizing the downstream side of the microfiltration unit.

  And it is comprised so that the ink waste_water | drain condensed from the said storage tank may be extracted intermittently.

  According to the treatment system configured as described above, the pigment is removed from the ink wastewater by microfiltration in the first treatment unit, and further, the coloring component, the organic component, etc. are brought into contact with ozone in the second treatment unit. The remaining components are decomposed. Accordingly, it is possible to effectively remove water-soluble ink components contained in the ink waste water and efficiently generate treated water that can be used as intermediate water.

  Moreover, since the microfiltration is performed by reducing the pressure on the downstream side, it is possible to prevent the pigment from being excessively trapped in the filtration membrane, and even when the ink drainage has a high pigment concentration, it can be filtered without causing sudden clogging. .

  Furthermore, since a microfiltration unit having a size smaller than that of the storage tank is installed in the storage tank, the amount of ink wastewater stored in the storage tank is suppressed, and a small amount of ink wastewater can be extracted. If the system is a separate process (using chemicals, etc.), the processing method, installation space, and running cost are required, but this system is easy to control with only a storage tank and a microfiltration unit.

  Further, by intermittently removing the ink waste water concentrated from the storage tank, clogging of the filtration membrane can be effectively prevented, and the ink waste water can be processed continuously and stably. As a result, the replacement frequency of the filtration membrane is reduced, and the running cost can be suppressed to a practical level.

  Specifically, the microfiltration unit has a plurality of hollow fiber membranes having a nominal pore diameter in the range of 0.1 μm to 0.45 μm, and the downstream side of the filtration unit is depressurized in a range not exceeding −50 kPa. It is good to be done.

  Then, the pigment can be separated with high accuracy while preventing the pigment from being excessively captured by the filtration membrane.

  More specifically, the microfiltration unit is arranged such that the plurality of hollow fiber membranes extend in a substantially vertical direction, and an air diffuser that discharges air from a plurality of openings is provided below the microfiltration unit. It should be arranged.

  Then, since the air released from the air diffuser into the ink drainage rises along the hollow fiber membrane, the direction in which the pigment is captured by the hollow fiber membrane (diameter direction of the hollow fiber membrane). A flow of ink drainage that is orthogonal to is formed. As a result, it is possible to effectively prevent the pigment from entering the inside of the hollow fiber membrane and being strongly captured, and clogging can be suppressed.

  Further, it is preferable that the downstream side of the microfiltration unit is pressurized periodically.

  Then, the filtered water is pushed out to the storage tank side, and the pigment trapped on the surface of the filtration membrane returns to the ink waste water, so that the progress of clogging can be delayed.

  For example, you may make it further provide the 3rd process part which contacts the activated water with the treated water processed by the said 2nd process part in the downstream of the said 2nd process part.

  By doing so, the decolorization and purification treatment of the ink waste water can be performed more stably.

  According to the present invention, it is possible to realize a water treatment system that can efficiently decolorize and purify ink waste water and reuse it as intermediate water.

It is the schematic which shows the processing system of the ink waste_water | drain of embodiment. It is a schematic perspective view which shows the principal part of a 1st process part. FIG. 3 is a schematic top view seen from the direction of arrow X in FIG. 2. It is the schematic sectional drawing seen from the direction of arrow Y in FIG. It is the schematic which shows the change of the pigment concentration in the storage tank in a process.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the following description is merely illustrative in nature and does not limit the present invention, its application, or its use.

(Processing system configuration)
FIG. 1 shows a configuration of a processing system 1 to which the present invention is applied.

  The processing system 1 is installed in a printing factory where water-soluble ink containing a pigment is used, such as flexographic printing. In such a printing factory, when a production lot is changed, water washing is performed on a pipe or the like through which water-soluble ink flows. At that time, a large amount of colored waste water (ink waste water) is generated.

  This ink drainage is simply a mixture of water-soluble ink in washing water, and unlike ordinary wastewater, there is usually almost no organic contamination. Therefore, this processing system 1 is devised to efficiently generate treated water that can be used as intermediate water by efficiently treating the removal target with water-soluble ink.

  Since the generated treated water can be reused as cleaning water, efficient cleaning can be realized without waste.

  As shown in FIG. 1, the ink drainage generated in the printing line is temporarily stored in the drainage tank 2. Ink wastewater is continuously or intermittently supplied from the drainage tank 2 to the treatment system 1 through the drainage pipe 3 in response to a request from the treatment system 1.

  The treatment system 1 includes a first treatment unit 10, a second treatment unit 30, and a third treatment unit 50, and three stages of water treatment are continuously performed under comprehensive control by the control device 4. It is configured to be performed.

  The control device 4 is a device that comprehensively controls the processing system 1 and includes various software such as a control program and various hardware that implements the software. Each process performed by the first processing unit 10, the second processing unit 30, and the third processing unit 50 is controlled by the control device 4.

(First processing unit)
In the 1st process part 10, the filtration process of an ink waste_water | drain is performed. The first processing unit 10 is provided with a storage tank 11, a microfiltration unit 12, an air diffuser 13, and the like, and is configured so that the pigment contained in the ink waste water can be efficiently separated.

  The main part of the 1st process part 10 is shown in FIGS. The storage tank 11 is a rectangular parallelepiped-shaped water tank that receives and stores ink wastewater from the drain tank 2. A drainage pump 15 for extracting the stored ink wastewater is installed inside the storage tank 11. A drainage path 14 extending to the outside of the storage tank 14 is connected to the drainage pump 15. The ink drainage stored in the storage tank 11 is intermittently extracted through the drainage path 14 (details will be described later).

  As shown in FIGS. 3 and 4, the microfiltration unit 12 is accommodated in the storage tank 11 so as to occupy most of the volume. The microfiltration unit 12 is dimensionally designed to correspond to the storage tank 11, and has an outer method that is slightly smaller than the inner method of the storage tank 11.

  Specifically, the dimensions are designed so that the volume of the microfiltration unit 12 occupies 20% or more of the volume of the storage tank 11. More specifically, the volume of the microfiltration unit 12 immersed in water in a state where the storage tank 11 is filled with water up to the set upper limit water level is the internal volume of the storage tank 11 up to the water level. It is configured to occupy 20% or more. In other words, the amount of stored water is designed to be reduced by 20% or more by installing the microfiltration unit 12.

  The microfiltration unit 12 includes ten filtration modules 16 having a prismatic appearance. These filtration modules 16 are densely arranged in a state of being arranged in two rows of five so that the side surfaces face each other with a gap.

  As shown in FIG. 2 and FIG. 4, each filtration module 16 includes a large number of elongated hollow fiber membranes 16 a and upper and lower support portions 16 b and lower supports that support both ends of the hollow fiber membranes 16 a that are closely arranged. Part 16c. The lower support 16c of each filtration module 16 is fixed to a rectangular frame 16d and connected to each other.

  The microfiltration unit 12 has a storage tank so that the upper support part 16b is located in the upper part of the storage tank 11, the lower support part 16c is located in the lower part of the storage tank 11, and the hollow fiber membrane 16a extends in a substantially vertical direction. 11 is arranged inside. During the filtering process, the water level of the ink waste water is adjusted so as to be at least above the upper support portion 16b. The level of the ink waste water is controlled by the control device 4 controlling the pump 3a installed in the drain tank 2 to adjust the amount of ink waste water sent to the storage tank 11.

  The hollow fiber membrane 16a is a known microfiltration membrane (PTFE membrane). The hollow fiber membrane 16a can be appropriately selected from membranes having a nominal pore diameter in the range of 0.1 μm to 0.45 μm based on processing conditions. In the processing system 1, a 0.2 μm microfiltration membrane is used.

  The hollow fiber membranes 16a of the filtration modules 16 communicate with each other via a communication space 16e formed inside the upper support portion 16b. A liquid collection pipe 17 is provided in the upper part of the microfiltration unit 12, and the liquid collection pipe 17 is arranged so as to extend between the filtration modules 16 arranged in two rows. A branch pipe 18 branches from both sides of the liquid collection pipe 17 toward each of the filtration modules 16 in each row. Each branch pipe 18 is connected to each upper support portion 16b and communicates with the communication space 16e.

  The liquid collection pipe 17 is connected to a water supply pipe 19 (water supply path) that sends filtered water (also referred to as first treated water) filtered by the microfiltration unit 12 to the second processing unit 30. A suction pump 20 that is driven and controlled by the control device 4 is installed in the middle of the water supply pipe 19. A pressure gauge 21 is installed in the water supply pipe 19 in the vicinity of the microfiltration unit 12. The pressure on the downstream side of the microfiltration unit 12 is measured by the pressure gauge 21.

  The downstream side of the microfiltration unit 12 is depressurized by the suction pump 20. Specifically, the downstream side of the microfiltration unit 12 is about -10 kPa if the hollow fiber membrane 16a is not clogged at all, and the pressure is reduced within a range not exceeding -50 kPa even if clogging occurs. To be controlled.

  By reducing the pressure with the suction pump 20, the ink wastewater stored in the storage tank 11 is filtered and sucked downstream of the microfiltration unit 12 through the hollow fiber membrane 16 a and flows into the water supply pipe 19.

  Thereby, since the pigment contained in the ink wastewater is trapped relatively gently in the hollow fiber membrane 16a than in the case where the upstream side of the microfiltration unit 12 is pressurized and filtered, clogging can be effectively suppressed. . Furthermore, since the pigment is easily captured by the hollow fiber membrane 16a, the pigment can be effectively removed from the ink waste water.

  The air diffuser 13 includes a blower 13 a that is driven and controlled by the controller 4, and an air diffuser 13 b that is connected to the blower 13 a and extends into the storage tank 11. The air diffuser 13b is disposed below the microfiltration unit 12. A plurality of apertures are formed in the air diffuser 13b. The blower 13a always operates during the filtration process. When the blower 13a is operated and air is supplied to the air diffuser 13b, a large amount of air is released into the ink drainage stored in the storage tank 11 through each opening.

  The air released into the ink drainage rises along the hollow fiber membrane 16a. Therefore, a flow of ink drainage perpendicular to the direction in which the pigment is sucked and captured by the hollow fiber membrane 16a (diameter direction of the hollow fiber membrane 16a) is formed along each hollow fiber membrane 16a. As a result, it is possible to effectively prevent the pigment from entering the interior of the hollow fiber membrane 16a and being strongly captured.

  The first treated water is sent to the second treatment unit 30 by the suction pump 20. The flow rate of the 1st treated water sent to the 2nd process part 30 is measured by the flowmeter 22, and the control apparatus 4 adjusts the water level of a processing tank based on the measured value.

(Second processing unit)
In the 2nd processing part 30, the ozone treatment of the 1st treated water is performed. The second treatment unit 30 is provided with an ozone contact tower 31, an ozone generator 32, a relay tank 35, and the like so that the coloring components and organic components remaining in the first treated water are efficiently decomposed. It is configured.

  The ozone contact tower 31 and the ozone generator 32 can be appropriately selected from known models according to processing conditions. For example, if it is the ozone generator 32 which can add 10-50 mg of ozone per liter of filtered water, it can be used conveniently.

  The ozone contact tower 31 is formed in a vertically long shape, and the first treated water is temporarily stored therein. The downstream end of the water supply pipe 19 is connected to the upper part of the ozone contact tower 31, and the first treated water flows from the upper part of the ozone contact tower 31 and is filled in the ozone contact tower 31. The upstream second water supply pipe 33 is connected to the lower part of the ozone contact tower 31, and the first treated water flows downward in the ozone contact tower 31 and flows out of the upstream second water supply pipe 33. .

  Below the ozone contact tower 31, an ozone supply pipe 34 extending from the ozone generator 32 into the ozone contact tower 31 is installed. During the ozone treatment, ozone is supplied into the ozone contact tower 31 through the ozone supply pipe 34. The first treated water comes into contact with ozone when passing through the inside of the ozone contact tower 31, and the coloring components and organic substances contained in the first treated water are decomposed by the oxidizing power of ozone.

  Between the 1st process part 10 and the 2nd process part 30, the reverse water supply path | route which flows back process water is provided.

  Specifically, the upstream second water supply pipe 33 extends to the relay tank 35 via the air vent 33a, and the first treated water (also referred to as second treated water) that has been subjected to ozone treatment in the ozone contact tower 31 is It is temporarily stored in the relay tank 35. Then, water is appropriately supplied to the third processing unit 50 through the downstream second water supply pipe 36 by the water supply pump 35a.

  An opening / closing valve 25 controlled by the control device 4 is installed in a portion between the microfiltration unit 12 and the suction pump 20 in the water supply pipe 19. A reverse water supply pipe 26 is connected to the water supply pipe 19 that branches from the upstream portion of the on-off valve 25 and extends to the relay tank 35. In the middle of the reverse water supply pipe 26, a water supply pump 27 that supplies the second treated water from the relay tank 35 toward the microfiltration unit 12 is installed. An opening / closing valve 28 controlled by the control device 4 is installed on the upstream side of the water supply pump 27 in the reverse water supply pipe 26.

(Third processing unit)
In the 3rd processing part 50, adsorption processing of the 2nd treated water is performed. The third treatment unit 50 is provided with an activated carbon contact tower 51 filled with particulate activated carbon, and the coloring components and organic components remaining in the second treated water are adsorbed and removed by activated carbon.

  The activated carbon contact tower 51 is formed in a vertically long shape, and the second treated water is temporarily stored therein. The downstream end of the downstream second water supply pipe 36 is connected to the upper part of the activated carbon contact tower 51, and the second treated water flows from the upper part of the activated carbon contact tower 51 and is filled inside the activated carbon contact tower 51.

  A third water supply pipe 52 is connected to the lower part of the activated carbon contact tower 51, and the second treated water flows downward in the activated carbon contact tower 51 and flows out of the third water supply pipe 52. The second treated water comes into contact with the activated carbon when passing through the inside of the activated carbon contact tower 51, and the coloring components and organic substances contained in the second treated water are adsorbed and removed by the activated carbon.

  Thereby, water having the quality of middle water (also referred to as third treated water) flows out from the third water supply pipe 52. An addition pipe 56 extending from a tank 55 for storing sodium hypochlorite is connected to the third water supply pipe 52, and a predetermined amount of sodium hypochlorite is supplied to the third treated water by the operation of the addition pump 57. Added. The third treated water to which sodium hypochlorite has been added is used for washing water, flush toilet water, sprinkling water, and the like.

(Operation of processing system)
In the processing system 1, the process of decolorizing and purifying the ink wastewater is performed continuously or intermittently for a long time by automatic operation.

  When the operation is started, first, the pump 3 a is operated and the ink drainage is sent from the drainage tank 2 to the storage tank 11. When the predetermined upper limit water level is reached, the suction pump 20 is activated. In a normal state, the open / close valve 25 is opened and the open / close valve 28 is closed so that the relay tank 35 does not communicate with the water supply pipe 19. Thereby, the ink wastewater is filtered to become the first treated water, which is sent to the ozone contact tower 31.

  When the first treated water flows into the ozone contact tower 31, the ozone generator 32 is activated and ozone is supplied into the ozone contact tower 31. When the ozone contact tower 31 is filled with the first treated water, the second treated water subjected to the ozone treatment flows into the relay tank 35. The second treated water is appropriately sent from the relay tank 35 to the activated carbon contact tower 51 and subjected to an adsorption treatment, whereby the third treated water flows out from the third water feeding pipe 52.

  After that, until the operation is stopped, the ink wastewater is supplied from the drainage tank 2 to the storage tank 11 and the third treated water is generated by the reduced amount. Therefore, as the process proceeds, the pigment separated by the filtration process accumulates in the storage tank 11, and the ink drainage in the storage tank 11 is concentrated with increasing pigment concentration over time. .

  The higher the pigment concentration, the more easily the hollow fiber membrane 16a is clogged. Therefore, in this processing system 1, the ink waste water concentrated from the storage tank 11 is intermittently extracted through the drainage path 14 before the pigment concentration reaches a predetermined concentration.

  The timing for extracting the ink waste water can be controlled by the control device 4. For example, if the concentration of the pigment contained in the ink wastewater is measured in advance, the accumulated amount of the pigment can be estimated from the supply amount of the ink wastewater. Then, the influence of the pigment accumulation amount on the clogging of the hollow fiber membrane 16a is examined, and the controller 4 may perform timer control based on the result.

  Therefore, in this processing system 1, every time the amount of ink wastewater supplied to the storage tank 11 reaches a predetermined amount, the entire amount of ink wastewater stored in the storage tank 11 is automatically extracted. .

  Specifically, when it is time to extract ink wastewater, the drainage pump 15 operates for a predetermined time by timer control, and the entire amount of ink wastewater is recovered from the storage tank 11 through the drainage path 14.

  In this processing system 1, the amount of ink wastewater stored in the storage tank 11 is suppressed by increasing the volume of the microfiltration unit 12 relative to the internal volume of the storage tank 11. As a result, the ink waste water can be collected little by little, which is efficient. Extraction can be done in a short time.

  If the system is a separate process (using chemicals or the like), the processing method, installation space, and running cost are required. However, in the case of this processing system 1, the control is simple with only the storage tank 11 and the microfiltration unit 12.

  Further, the treatment system 1 is configured such that the reverse water supply treatment is performed periodically, such as every two hours, during the continuous treatment.

  That is, a control program for performing a reverse water supply process is installed in the control device 4, and the water supply pump 27, the open / close valves 25, 28 and the like are operated based on the control program. Specifically, when the water treatment continues for a predetermined time, the suction pump 20 is stopped, the on-off valve 25 is closed and the on-off valve 28 is opened, so that the water supply pipe 19 and the reverse water supply pipe 26 communicate with each other. Switch to state.

  Then, the water pump 27 is activated, and the filtered water inside the relay tank 35 is sent to the microfiltration unit 12. Thereby, the downstream side of the microfiltration unit 12 in which filtered water exists is pressurized, and the filtered water is pushed out to the storage tank 11 side through the hollow fiber membrane 16a. Along with this, the pigment trapped in the pores on the surface of the hollow fiber membrane 16a is pushed out and returned to the ink waste water, so that the progress of clogging of the hollow fiber membrane 16a can be delayed.

  When the reverse water supply treatment is performed for a predetermined time, the water supply pump 27 is stopped, the on-off valve 25 and the on-off valve 28 are switched to the original state, the suction pump 20 is operated again, and the water treatment is resumed.

  FIG. 5 is a graph schematically showing a change over time in the pigment concentration of the ink wastewater stored in the storage tank 11. In the figure, R represents a reverse water supply process, and B represents a sampling process.

  Assuming that the pigment concentration of the treated ink wastewater is C0, the pigment concentration in the storage tank 11 gradually increases from C0 as the water treatment proceeds. And every time predetermined time passes, a reverse water supply process is performed. As a result, the hollow fiber membrane is regenerated, and even if the pigment concentration is high, filtration can be performed while clogging is suppressed. Then, when the pigment concentration of the ink wastewater reaches a predetermined C1, extraction processing is performed.

  Since the amount of storage is small, it can be extracted efficiently in a short time. By the extraction process, the pigment concentration of the ink waste water in the storage tank 11 returns to the initial C0. Thereafter, the ink waste water is continuously processed while repeating the reverse water supply process and the extraction process in the same manner.

(Other)
The processing system 1 according to the present invention is not limited to the above-described embodiment, and includes various other configurations.

  For example, the third processing unit 50 is not essential. In the case where processing up to the second processing unit 30 can achieve the desired water quality, the third processing unit 50 may be omitted. Not only middle water but also treated water that can be used as clean water may be generated. For this purpose, a fourth processing unit or the like may be provided.

  A particle counter that measures the concentration of the pigment in the ink wastewater may be installed in the drainage pipe 3, and the ink wastewater may be extracted based on the measured value. In this case, since the density | concentration of the pigment which accumulates in the storage tank 11 can be measured directly, more stable timing control is realizable.

  The reverse water supply treatment is preferably performed in such a manner that the continuous treatment time becomes longer, that is, the execution timing becomes shorter as the pigment concentration becomes higher. Then, the progress of clogging can be delayed more effectively.

  You may perform a reverse water supply process just before a sampling process or in the middle of a sampling process. If it does so, a pigment can be efficiently excluded from the storage tank 11. FIG.

  The forms of the storage tank and the microfiltration unit, including the number and arrangement of the filtration modules, can be appropriately changed according to the specifications.

DESCRIPTION OF SYMBOLS 1 Processing system 2 Drainage tank 4 Control apparatus 10 1st process part 11 Storage tank 12 Microfiltration unit 13 Aeration apparatus 14 Drainage path 16 Filtration module 19 Water supply piping 20 Suction pump 21 Pressure gauge 22 Flowmeter 25, 28 On-off valve 26 Reverse Water supply pipe 27 Water supply pump 30 Second treatment section 31 Ozone contact tower 32 Ozone generator 33 Upstream second water supply pipe 34 Ozone supply pipe 35 Relay tank 36 Downstream second water supply pipe 50 Third treatment section 51 Activated carbon contact tower 52 First 3 water supply piping

Claims (5)

A treatment system that produces treated water that can be used at least as intermediate water by treating ink wastewater containing pigment,
A first processing unit for precisely filtering ink wastewater;
A second treatment unit for contacting the filtered water treated in the first treatment unit with ozone;
With
The first processing unit includes:
A reservoir for receiving ink waste,
A microfiltration unit that has an outer method slightly smaller than the inner method of the storage tank, and is accommodated in the storage tank,
A water supply path connected to the microfiltration unit and sending filtrate to the second treatment unit;
A suction pump for decompressing the downstream side of the microfiltration unit;
Have
An ink wastewater treatment system in which concentrated ink wastewater is intermittently extracted from the storage tank. The ink wastewater treatment system according to claim 1,
The microfiltration unit has a plurality of hollow fiber membranes having a nominal pore diameter in the range of 0.1 μm to 0.45 μm,
An ink wastewater treatment system in which the downstream side of the filtration unit is depressurized within a range not exceeding −50 kPa. The ink wastewater treatment system according to claim 2,
The microfiltration unit is arranged such that the plurality of hollow fiber membranes extend in a substantially vertical direction,
An ink wastewater treatment system in which an air diffuser that discharges air from a plurality of openings is disposed below the microfiltration unit. The ink wastewater treatment system according to any one of claims 1 to 3,
An ink wastewater treatment system in which the downstream side of the microfiltration unit is periodically pressurized. The ink wastewater treatment system according to any one of claims 1 to 4,
An ink wastewater treatment system further comprising a third treatment unit that brings the treated water treated by the second treatment unit into contact with the activated carbon on the downstream side of the second treatment unit.

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