JP2008221070A - Gas-liquid contacting device and gas-liquid contacting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas-liquid contacting device which is capable of discharging accumulated water in a hollow fiber and has high efficiency of gas-liquid contacting, and to provide a gas-liquid contacting method using the gas-liquid contacting device. <P>SOLUTION: A hollow fiber module 15 in which a plurality of hollow fibers 14 are bundled and the hollow fibers are united with one another only on the lower part side by a uniting member 13 is located in a housing 12. A gas reservoir part 16 is formed on the upper part in the housing 12, the upper end parts of the hollow fibers 14 are located in the gas reservoir part 16, and flow and aeration are performed so that such a state that the lower side of the hollow fibers 14 is immersed into liquid rather than the upper end parts thereof. Gas supplied from a gas inlet 12c to the gas reservoir part 16 flows from the upper end side of the hollow fibers 14 to the lower end sides. Microorganisms in water attach to the outer circumferential surfaces of hollow fibers 14 and biological membranes are formed on the outer circumferential surfaces of hollow fibers 14. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a gas-liquid contact device in which a gas is supplied into a hollow fiber and the gas passes through the hollow fiber and comes into contact with a liquid, and a gas-liquid contact method using the gas-liquid contact device.

  In the present specification, the inner hole of the hollow fiber means an inner hole penetrating the tubular hollow fiber in the longitudinal direction, and the hollow hole of the hollow fiber means a synthetic resin constituting the wall portion of the hollow fiber. Means the micropores present in

I. In order to increase the efficiency of biological treatment methods for wastewater, it has been studied to maintain microorganisms responsible for treatment at a high concentration in a reaction tank and to supply oxygen to wastewater at a low cost.

  In order to maintain a high concentration of microorganisms, a method of putting a gel containing microorganisms in a fixed manner into a biological treatment tank, a fixed bed or a fluidized bed in which microorganisms are attached to a plastic molded product, sponge, or the like have been put into practical use.

  On the other hand, in order to efficiently supply oxygen, a method using pure oxygen and an efficient air diffuser for blowing fine bubbles into sewage have been devised. However, the method using pure oxygen has a problem that the production cost of oxygen is comparable to that of a normal method in which air is blown, and in the refinement of bubbles, the power related to physical energy is increased. That was a challenge. In order to solve these problems, a method of transferring oxygen directly from the air to the liquid phase via a hollow fiber membrane has been studied.

II. FIG. 2 shows a longitudinal sectional view of a conventional gas-liquid contact device 1A using a hollow fiber. This gas-liquid contact device 1A has a casing 2A and a hollow fiber module 5A.

  The casing 2A has a substantially cylindrical shape with an open upper end and a closed lower end. A liquid inlet 2a is provided at the upper part of the side surface, and a liquid outlet 2b is provided at the lower part of the side surface. A gas discharge port 2c is provided above the inflow port 2a.

  In the hollow fiber module 5A, a plurality of hollow fibers 4 are bundled together, and the upper side of the bundle is bound to each other by a binding member 3 made of synthetic resin or the like. The upper end of each hollow fiber 4 is open, and the lower end 4e is sealed.

  The hollow fiber module 5A is arranged so that the hollow fiber 4 is inserted into the casing 2A, and the binding member 3 is brought into contact with the flange portion 2f at the upper end of the casing 2A via the packing 9, and the bolt 7 and the nut The flange portion 2 f and the bundling member 3 are connected by 8.

  When operating the gas-liquid contact device 1A, the liquid is supplied from the inflow port 2a and the liquid is discharged from the outflow port 2b. Further, gas is supplied into the hollow fiber 4 from the upper end of the hollow fiber 4. This gas passes through the hollow fiber 4 and is supplied to the liquid in the casing 2A. Further, gas is discharged from the gas discharge port 2c to the outside of the casing 2A. Note that the upper part in the casing 2 </ b> A is not filled with the liquid, and the upper part becomes the gas reservoir 6.

  The hollow fiber membrane module shown in FIG. 2 has a “dead end” structure in which the lower end 4 e is closed, and therefore, moisture generated inside the hollow fiber 4 cannot be discharged. Further, in this structure, the air purged inside the hollow fiber 4 is both in the upper part of the hollow fiber 4 than the liquid level (the part located in the air reservoir 6) and the lower part of the liquid level. However, since the hollow fiber portion below the water surface is a dead end and there is no gas outlet, oxygen in the air reaches the bottom of the column by molecular diffusion. However, since the rate of molecular diffusion is several orders lower than the amount of purge, there is also a problem that the biofilm at the bottom of the module becomes oxygen-limited. Furthermore, since the inside of the hollow fiber 4 is hollow, the hollow fiber 4 is lifted by buoyancy, and there is a problem that it is difficult to uniformly fill the casing 2A.

  FIG. 3 shows a longitudinal sectional view of a different conventional gas-liquid contact device 1B.

  The casing 2B of the gas-liquid contact device 1B has a substantially cylindrical shape with the upper end opened and the lower end closed. A liquid inlet 2a is provided at the lower part of the side surface, a liquid outlet 2b is provided at the upper part of the side surface, and an outlet 2d is provided at the bottom surface.

  In the hollow fiber module 5B, a plurality of hollow fibers 4 are arranged in a bundle, and the upper side and the lower side of the bundle are bound to each other by binding members 3 and 3A made of synthetic resin or the like. The outer diameter of the binding member 3A is smaller than the inner diameter of the casing 2B. Both ends of each hollow fiber 4 are open.

  A receiving member 3B is fastened to the lower surface of the binding member 3A.

  The receiving member 3B has an open container shape, and a nozzle portion 3b extends downward from the center of the lower surface. The upper end surface of the receiving member 3B is brought into contact with the peripheral edge of the lower surface of the binding member 3A and is connected by a bolt 3g and a nut 3h.

  The hollow fiber module 5 is arranged so that the hollow fiber 4 is inserted into the casing 2B, and the binding member 3 is brought into contact with the flange portion 2f at the upper end of the casing 2B via the packing 9, and the bolt 7 and the nut 8 are connected. Further, the nozzle portion 3b of the receiving member 3B is inserted through the outlet 2d. An O-ring 2e is interposed between the nozzle portion 3b and the outlet 2d.

  When operating the gas-liquid contact device 1B, the liquid is supplied from the inflow port 2a and the liquid is discharged from the outflow port 2b. Moreover, gas is supplied into the hollow fiber 4 from the upper end of the hollow fiber 4, and is exhausted out of the casing 2B through the receiving member 3B. A part of the gas supplied into the hollow fiber 4 passes through the pores of the hollow fiber 4 and is supplied to the liquid in the casing 2B.

  When both ends of the hollow fiber are firmly fixed as in the gas-liquid contact device 1B of FIG. 3, there is an advantage that the hollow fiber 4 can be uniformly filled in the casing 2B, but the inside of the hollow fiber bundle (center side) The hollow fiber has a disadvantage that it is difficult to come into contact with water. If the hollow fiber and water are difficult to contact, the substantial effective area of the biofilm will decrease, and the biological treatment efficiency will decrease.

III. In general, when adopting a method of transferring oxygen directly from air to the liquid phase via a porous hollow fiber membrane, when the gas molecules in the gas move to the liquid phase, first, the molecules are at the gas-liquid interface. The film (gas film / liquid film) must be diffused, but the movement resistance of the liquid film is quite high. These films are always formed in bubbles. This characteristic becomes a problem when air is blown (aerated). On the other hand, a hydrophobic film has a characteristic of repelling liquid by high surface tension.

  Therefore, as schematically shown in FIG. 4 (a), if the biological membrane 10 is formed on the surface of the hollow fiber 4 made of a porous hydrophobic membrane, the oxygen gas is directly passed through the liquid boundary membrane. In addition, it can come into contact with the biofilm on the surface of the hollow fiber. The code | symbol 4a shows the pore of a hollow fiber membrane. In general, the movement resistance of the gas boundary film is extremely small and can be ignored. For this reason, the hydrophobic hollow fiber can be an efficient oxygen supply device.

  U.S. Pat. No. 4,181,604 is a patent document in which wastewater is treated by forming a biofilm on the hollow fiber surface. The waste water treatment apparatus of the same publication has a configuration in which hollow fibers are arranged in a loop shape in a container having a liquid inlet and outlet, and both ends of the hollow fiber are connected to an air supply pipe. Then, the liquid is supplied from the inlet and the liquid is discharged from the outlet, and the gas is supplied from both ends of the hollow fiber through the air supply pipe, and the gas passes through the hollow fiber and is supplied to the liquid. Is done.

  However, this type of hydrophobic hollow fiber has the following drawbacks.

  (I) As shown in FIG. 4 (b), condensation occurs inside the hollow fiber 4 (reference numeral 11 indicates water droplets generated by condensation), and the inner hole of the hollow fiber may be clogged.

  (Ii) The bubble point (the critical pressure at which bubbles begin to be generated from the membrane surface when gas is pushed in) is much lower than that of a gas separation membrane having a skin layer. Will occur and the attached biofilm will peel off.

In order to cope with this, as shown in FIG. 5, studies have been made to supply oxygen using a hollow fiber 4B having a skin layer 4b which does not condense and has a high bubble point. However, in this case, since the movement resistance in the skin layer 4b is as high as that of the liquid boundary film, it is not possible to expect mass transfer as efficiently as the hydrophobic film.
US Pat. No. 4,181,604

  It is an object of the present invention to provide a gas-liquid contact device that can discharge the staying liquid in the hollow fiber and has high gas-liquid contact efficiency, and a gas-liquid contact method using the gas-liquid contact device. .

  The gas-liquid contact device of the present invention (Claim 1) is obtained by arranging a hollow fiber module having a plurality of hollow fibers in a vertical direction in a casing having a liquid inlet and outlet. In the gas-liquid contact device in which the liquid is supplied, the gas is supplied into the hollow fiber, and the gas passes through the hollow fiber and comes into contact with the liquid, both ends of the hollow fiber are open, The upper end of the hollow fiber is located at the upper part in the casing, and the lower end of the hollow fiber communicates with the outside of the casing, and the hollow fibers are bound to each other only on the lower side and are free on the upper side. The gas inlet is provided in the upper part of the casing, and the gas introduced into the casing from the gas inlet vents through the hollow fiber from the upper end side toward the lower end side. It is characterized by that.

  A gas-liquid contact device according to a second aspect is characterized in that, in the first aspect, a gas supply device for supplying gas to the gas introduction port is provided.

  A gas-liquid contact device according to a third aspect is characterized in that, in the first or second aspect, means for reducing the dew point of the gas supplied to the gas inlet is provided.

  According to a fourth aspect of the present invention, there is provided the gas-liquid contact device according to any one of the first to third aspects, further comprising a filter for the gas supplied to the gas inlet.

  According to a fifth aspect of the present invention, the gas-liquid contact device according to any one of the first to fourth aspects is characterized in that the liquid is water and the hollow fiber is a hydrophobic membrane.

  The gas-liquid contact device of claim 6 is characterized in that, in claim 5, the hollow fiber is made of at least one member selected from the group consisting of polytetrafluoroethylene, polysulfone, polyethylene, and polyvinylidene difluoride. is there.

  A gas-liquid contact device according to a seventh aspect is characterized in that, in the fifth aspect, the hollow fiber is made of a microfiltration membrane or an ultrafiltration membrane.

  The gas-liquid contact device according to claim 8 is characterized in that, in any one of claims 5 to 7, a biofilm is formed on the outer surface of the hollow fiber.

  A gas-liquid contact device according to a ninth aspect is characterized in that, in the eighth aspect, means for peeling the biofilm is provided.

  The gas-liquid contact method of the present invention (Claim 10) is a gas-liquid contact method using the gas-liquid contact device according to any one of claims 1 to 9, wherein a gas pool is formed in an upper portion of the casing. And the upper end of the hollow fiber is located in the gas reservoir, and the lower side of the upper end is submerged in the liquid. While circulating through the casing, gas is introduced into the upper part of the casing from the gas inlet, and gas is vented from the upper end side to the lower end side of the hollow fiber.

  The gas-liquid contact method of claim 11 is characterized in that, in claim 10, the pressure of the gas supplied into the hollow fiber is not less than atmospheric pressure and not more than 1.1 atm.

  A gas-liquid contact method according to a twelfth aspect is characterized in that, in the tenth or eleventh aspect, a biofilm is formed on the outer surface of the hollow fiber by gas-liquid contact.

  A gas-liquid contact method according to a thirteenth aspect is characterized in that in the twelfth aspect, the biofilm is peeled off when the biofilm grows to a predetermined level or more.

  A gas-liquid contact method according to a fourteenth aspect is characterized in that, in the thirteenth aspect, the biofilm is peeled off by supplying bubbles into the casing or increasing a liquid passing speed in the casing. Is.

  In the gas-liquid contact device (Claim 1) and the gas-liquid contact method (Claim 10) of the present invention, since the upper end portion of the hollow fiber is located in the gas reservoir portion, the hollow is introduced from the gas inlet at the upper part of the casing. Gas flows through the inner hole of the hollow fiber through the upper end of the yarn. This gas flows out from the lower end of the hollow fiber, but is supplied to the liquid through the pores of the hollow fiber along the way.

  In the present invention, since the hollow fibers are bound to each other only on the lower side and are in a free state on the upper side, the hollow fibers are freely swayed by the liquid flow when passing through the casing. As a result, the hollow fiber on the center side of the hollow fiber module can easily come into contact with the circulating liquid, and as a result, the gas that has passed through the hollow fiber is efficiently supplied to the liquid.

  In general, when gas is supplied into the hollow fiber, moisture in the gas is condensed, condensation occurs in the hollow fiber, and the inner hole of the hollow fiber may be blocked by water droplets due to the condensation. According to the gas-liquid contact device and the gas-liquid contact method of the present invention, the gas supplied into the hollow fiber flows downward, so that the water droplet generated in the hollow fiber is hollow due to the downward flow of this gas and the weight of the water droplet. The yarn is quickly discharged from the lower end side of the yarn.

  In the gas-liquid contact device of the second aspect, the gas can be supplied from the upper end of the hollow fiber into the hollow fiber by the air supply device.

  In the gas-liquid contact device according to the third aspect, since means for reducing the dew point of the gas supplied to the gas inlet is provided, it is possible to suppress the generation of water droplets due to the condensation of the gas in the hollow fiber.

  Since the gas-liquid contact device according to the fourth aspect is provided with the gas filter, impurities mixed in the gas are prevented from entering the inner hole of the hollow fiber and clogging the hollow fiber.

  In the gas-liquid contact device according to the fifth aspect, since the hollow fiber is a hydrophobic membrane, water outside the hollow fiber is prevented from entering the hollow fiber membrane through the pores.

  The hollow fiber membrane is preferably made of at least one member selected from the group consisting of polytetrafluoroethylene, polysulfone, polyethylene, and polyvinylidene difluoride (Claim 6). In addition, in order to improve hydrophobicity, you may further water-repellently process the hollow fiber which consists of these materials.

  The gas-liquid contact device of claim 7 has a small pore diameter because the hollow fiber is made of a microfiltration membrane or an ultrafiltration membrane. This prevents water from entering the hollow fiber and bacterial growth.

  Even when the hollow fiber is made of a hydrophobic material, if the hollow fiber has a large pore diameter, water enters the inner hole in the hollow fiber. In addition, when a biofilm is formed on the outer peripheral surface of the hollow fiber, bacteria grown on the biofilm grow in the hollow fiber through the pores, and the inner hole of the hollow fiber becomes clogged. According to the seventh aspect, such a problem is solved.

  In the gas-liquid contact device of claim 8 and the gas-liquid contact method of claim 12, since a biofilm is formed on the outer surface of the hollow fiber, a gas containing oxygen is fed into the hollow fiber and the casing When water to be treated is passed through, oxygen that has permeated through the hollow fiber is efficiently supplied to the biofilm, and water treatment by the organism is efficiently performed.

  As described above, when the biofilm is formed on the outer surface of the hollow fiber, the biological treatment is performed with high efficiency, so that it is not necessary to separately perform the water treatment using the activated sludge floc. For this reason, it is not necessary to provide a large-area concentration tank necessary for solid-liquid separation of the activated sludge floc, and the apparatus can be made compact.

  In addition, in order to make the water after biological treatment with the biofilm clearer water, a flocculant can be added and solid-liquid separation can be performed in the gravity concentration tank. Since the SS (floating matter) concentration of water after treatment is low and the sedimentation rate of the peeled biofilm is fast, a small gravity concentration tank is sufficient.

  In the hollow fiber in which such a biofilm is formed, the hollow fibers adhere to each other through the biofilm, and the liquid may not be easily passed through the hollow fiber on the center side of the hollow fiber module.

  Since the gas-liquid contact device of claim 9 and the gas-liquid contact method of claim 13 have means for peeling the biofilm, the biofilm grown more than a predetermined value can be peeled from the hollow fiber. As a result, the hollow fibers are prevented from adhering to each other via the biofilm, and the hollow fibers on the center side of the hollow fiber module are sufficiently passed through, so that the liquid is efficiently purified.

  For example, the biofilm can be peeled off by supplying air bubbles into the casing or increasing the liquid passing speed inside the casing.

  In the gas-liquid contact method according to claim 11, since the pressure of the gas supplied into the hollow fiber is a low pressure of atmospheric pressure to 1.1 atm, the apparatus for supplying the gas can be reduced in cost and operated. Cost can be reduced.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic cross-sectional view of a gas-liquid contact device 1 according to an embodiment.

  The gas-liquid contact device 1 mainly includes a casing 12 and a hollow fiber module 15.

  The casing 12 has a cylindrical shape with an open lower end. A liquid inflow port 12 a is provided in the upper part of the peripheral surface of the casing 12, and an outflow port 12 b is provided in the lower part. A gas inlet 12 c is provided at the top of the casing 12.

  In this hollow fiber module 15, a plurality of hollow fibers 14 are arranged in a bundle, and the hollow fibers 14 are bound together by a binding member 13 made of a synthetic resin only on the lower side. The upper side of the binding member 13 of the hollow fiber 14 is not restrained and is in a free state. The binding member 13 has a disk shape, and the upper half of the binding member 13 is a small diameter portion inserted into the casing 12. The lower half of the binding member 13 is a large diameter portion that is larger than the inner diameter of the casing 12. Both ends of the hollow fiber 14 are not sealed and are open.

  In the case where a biological film is formed on the hollow fiber 14 and biological treatment of water containing organic matter, ammonia or the like is performed, it is preferable to use a hydrophobic film as the hollow fiber 14. This prevents water outside the hollow fiber 14 from entering the hollow fiber 14. Examples of the material of the hydrophobic membrane include at least one member selected from the group consisting of polytetrafluoroethylene, polysulfone, polyethylene, and polyvinylidene difluoride.

  As the hollow fiber 14, it is preferable to use a microfiltration membrane or an ultrafiltration membrane having a small pore diameter. In this case, since the pore diameter of the hollow fiber 14 is sufficiently small, bacteria grown on the biofilm are prevented from growing in the hollow fiber 14 through the pore and clogging the hollow fiber. In order to increase the permeability of oxygen in the gas, it is preferable to use a microfiltration membrane, particularly a microfiltration membrane having a nominal pore diameter of about 0.02 to 0.2 μm.

  In order to attach the hollow fiber module 15 to the casing 12, the hollow fiber 14 of the hollow fiber module 15 is inserted from the lower end side of the casing 12. Then, a small diameter portion on the upper half side of the binding member 13 is inserted into the lower end portion of the casing 12, and the large size of the binding member 13 is interposed via a packing 19 with respect to a flange 12 f provided on the outer periphery of the lower end portion of the casing 12. The diameter part is brought into contact. Next, these flanges 12 f and the large diameter portion are connected using bolts 17 and nuts 18.

  The gas inlet 12 c is connected to the air supply device 20 via a pipe 21. As the air supply device 20, a fan, a blower or the like is suitable. The pressure of the gas vented into the hollow fiber 14 may be not less than atmospheric pressure, and the discharge pressure of the air supply device is preferably not less than atmospheric pressure and not more than 1.6 atm, particularly preferably not less than atmospheric pressure and not more than 1.1 atm. If the discharge pressure is too high, the aeration power cost increases. This discharge pressure is appropriately selected according to the inner diameter, length, etc. of the hollow fiber 14. The hollow fiber module 15 in which 1000 to 10,000 hollow fibers having an inner diameter of 0.6 mm and a length of 5 to 10 m are aligned can be ventilated with a commercially available fan having a discharge pressure of 0.05 to 0.15 atm. it can.

  Next, an example of a gas-liquid contact method using the gas-liquid contact device 1 will be described.

  Water containing organic matter, ammonia or the like is supplied from the inlet 12a into the casing 12 and flows out from the outlet 12b. Further, an oxygen-containing gas such as air is supplied from the gas inlet 12 c to the gas reservoir 16, and the gas is vented from the upper end side to the lower end side of the hollow fiber 14. At this time, as shown in FIG. 1, a gas reservoir 16 is formed in the upper part of the casing 12, the upper end of the hollow fiber 14 is located in the gas reservoir 16, and the lower side of the upper end is liquid. Adjust the water flow rate, water flow pressure, air supply pressure, and air supply rate so as to be immersed in the water.

  A part of the gas supplied into the hollow fiber 14 passes through the pores of the hollow fiber 14 and is supplied to the water flowing outside the hollow fiber 14. The remainder of the gas supplied into the hollow fiber 14 is discharged from the lower end side of the hollow fiber 14.

  When the operation is continued, microorganisms such as organic substances in water and bacteria adhere to the outer peripheral surface of the hollow fiber 14, and a biofilm is gradually formed on the outer peripheral surface of the hollow fiber 14. Thereby, oxygen supplied from the hollow fiber membrane 14 is directly supplied to the biological membrane, and oxygen is efficiently used for oxidation of a substance to be treated such as ammonia.

  Even if condensed water is generated in the hollow fiber 14, the condensed water is quickly discharged from the lower end of the hollow fiber 14.

  The above embodiment is an example of the present invention, and the present invention is not limited to the above embodiment. For example, in the gas-liquid contact device 1 of FIG. 1, a filter for removing solids or the like in the liquid may be provided upstream of the inlet 12a.

  Further, means for reducing the dew point of the gas may be provided on the piping 21 or the suction side of the air supply device 20. Examples of means for reducing the dew point of the gas include a dehumidifier in which a container is filled with silica gel, a refrigeration dryer, a membrane dryer, and the like.

  Furthermore, the biofilm may be peeled from the hollow fiber 14 when the biofilm grows more than a predetermined amount. For example, a gas pipe may be installed in the lower part of the casing 12, and when the biofilm has grown more than a predetermined amount, bubbles may be supplied into the casing 12 from the gas pipe. Gas-liquid mixed water may be supplied instead of bubbles. Further, when the biofilm grows to a predetermined level or more, the biofilm may be peeled off by increasing the flow rate of the liquid supplied from the inlet 12a into the casing 12.

  Hereinafter, Example 1 and Comparative Example 1 will be described.

[Example 1]
The operation was performed using the gas-liquid contact device of FIG.

As the hollow fiber 14, 2200 microfiltration hollow fibers (nominal pore diameter 0.1 μm, membrane area 7 m ² ) made of polysulfone having an outer diameter of 1.0 mm, an inner diameter of 0.6 mm, and a length of 1000 mm were used. As the casing 12, a hard vinyl chloride column having an inner diameter of 100 mm, a height of 1200 mm, and an effective volume of 8 L was used. In this gas-liquid contact device, the membrane area of the hollow fiber per column unit volume is 875 m ² / m ³ .

  Through this gas-liquid contact device, synthetic nutrient wastewater containing 100 mg-N / L of ammonia is passed at 100 L / day, and air is vented downward at 3 L / min from the gas inlet 12 c to form hollow fibers. Continuous operation for forming a biofilm of nitrifying bacteria on the surface of 14 was performed. By adjusting the water flow amount, water flow pressure, air amount, and air pressure, the air reservoir 16 having a height of 200 mm was formed on the upper portion of the casing 12.

  The ammonia concentration and dissolved oxygen concentration of water flowing out from the outlet 12b were recorded over time. Based on the amount of ammonia oxidized to nitric acid, the amount of oxygen supplied to the hollow fiber 14 was determined according to the following equation (1).

NH ₃ + 1.5O ₂ → NO ₂ ⁻ + H ⁺ + H ₂ O
NH ₃ + 2O ₂ → NO ₃ ⁻ + H ⁺ + H ₂ O
Oxygen supply ^{_{(g-O 2 / m 2}} / day)
= {Nitrous acid amount flowing out into treated water × (1.5 × 32/14) + Nitric acid amount flowing out into treated water × (2 × 32/14)} ÷ 7 m ² (1)

  Since the pH of the gas-liquid contact device was lowered with the nitrification of ammonia, neutralizing ammonia water was automatically added as the pH decreased.

  Since this ammonia water also serves as a substrate for nitrifying bacteria, the supply amount of ammonia water automatically increases as the biofilm activity (nitrification) increases. Since the supplied ammonia is quickly oxidized to nitrous acid and nitric acid, the oxygen consumption of the gas-liquid contact device (the oxygen supply amount of the hollow fiber is measured by measuring the nitrous acid concentration and nitrate concentration over time of the treated water. ).

  FIG. 6 shows the result of continuous operation using this apparatus. FIG. 6 is a graph showing the relationship between the number of operating days and the oxygen absorption rate per unit membrane area, and the operating days and the dissolved oxygen concentration of the effluent water from the gas-liquid contact device.

<Discussion>
In about 500 days of continuous operation, the number of biofilms gradually increased on the surface of the hollow fiber. Correspondingly, as shown in FIG. Thereafter, the oxygen absorption rate began to change at a substantially constant value of 25 to 30 gO ₂ / m ² / day. The dissolved oxygen concentration of the effluent water from the gas-liquid contact device has a value close to the saturation concentration because the amount of biofilm is small in the initial stage of operation and the amount of supply from the hollow fiber is larger than the oxygen absorption rate of the organism. However, as the amount of biofilm gradually increased, it gradually decreased and became constant at about 1 mg / L. This is because the fully grown biofilm is nitrifying ammonia at the maximum rate.

In this gas-liquid contact device, the membrane area per column unit volume is 875 m ² / m ³ , so the oxygen absorption rate per reactor unit volume is 21.9 to 26.3 kgO ₂ / m ³ / day. This means that this gas-liquid contact device has an oxygen supply capacity approximately 10 times that of a normal aeration tank used for activated sludge treatment (an equivalent treatment with a volume of 1/10 of a normal aeration tank). Performance).

  When about 200 days passed after the operation was started, it was visually observed that a thick biofilm was attached to the hollow fiber. This biofilm was peeled off by a water flow, but when the water flow was increased or aeration was performed by aeration of gas through a gas-liquid contact device, the amount of biofilm peeled increased. After this operation, the head loss of the column was reduced by about 50 mm, and it was found that by performing these operations, it is possible to control undesirable phenomena in the operation of the apparatus including an increase in pressure due to excessive growth of the biofilm. This is an especially important operation when using an air supply device such as a fan that cannot increase the ventilation pressure.

  As the operation continued, a very small amount of water (about 30 mL / day) began to flow out from the hollow fiber outlet at the bottom of the column. This water component was close to distilled water and contained almost no salt. From this, it was determined that this water was condensed water inside the hollow fiber. The generation of water causes corrosion of the machinery constituting the gas-liquid contact device, or oligotrophic microorganisms such as mold are generated, and the outlet of the hollow fiber is contaminated and blocked. Therefore, when operations such as changing the temperature of the aeration gas and lowering the dew point were performed, such water was no longer generated.

[Comparative Example 1]
The operation was performed in the same manner as in Example 1 except that the gas-liquid contact device of FIG. 2 was used. The type, size, and number of hollow fibers were the same as in Example 1. The result is shown in FIG.

As shown in FIG. 7, the dissolved oxygen concentration of the gas-liquid contact device decreases relatively early, and the oxygen absorption rate per unit membrane area is about 1/10 of that of the example, _{2 to 3} gO ₂ / m ^2. / Day became constant.

  On the 220th day after the start of operation, the gas-liquid contactor was opened and the state of the hollow fiber was examined. As a result, there was not much water accumulated inside the hollow fiber, but there was almost no biofilm in the hollow fiber behind the bundle. It was found that it was not attached. This is thought to be because the hollow fiber bundle was fixed at the top and bottom, making it difficult for the hollow fiber in the back to come into contact with water and the oxygen supply stagnating. When the oxygen supply is delayed, oxygen is not properly supplied from the hollow fiber to the biofilm. This is considered to be the reason why the oxygen absorption rate (oxygen supply rate) in Comparative Example 1 is significantly lower than that in Example 1.

It is sectional drawing which shows a gas-liquid contact apparatus in embodiment. It is sectional drawing which shows the conventional gas-liquid contact apparatus. It is sectional drawing which shows a different conventional gas-liquid contact apparatus. (A) is a typical expanded sectional view which shows the state in which the biofilm was formed in the outer peripheral surface of a hollow fiber, (b) is a typical expanded sectional view which shows the state in which the water droplet generate | occur | produced in (a). is there. It is a typical expanded sectional view which shows the state in which the biofilm was formed in the outer peripheral surface of the hollow fiber which has a skin layer. 3 is a graph showing the results of Example 1. 6 is a graph showing the results of Comparative Example 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Gas-liquid contact apparatus 12 Casing 12a Inlet 12b Outlet 12c Gas inlet 13 Bundling member 14 Hollow fiber 15 Hollow fiber module 16 Gas reservoir part 19 Packing 20 Air supply apparatus

Claims (14)

A hollow fiber module having a plurality of hollow fibers is arranged in a vertical direction in a casing having an inflow port and an outflow port for liquid, and liquid is supplied into the casing, and gas is introduced into the hollow fiber. In the gas-liquid contact device that is supplied and the gas passes through the hollow fiber and comes into contact with the liquid,
Both ends of the hollow fiber are open,
The upper end of the hollow fiber is located at the upper part in the casing, and the lower end of the hollow fiber communicates with the outside of the casing,
The hollow fibers are bound together only on the lower side, and are in a free state on the upper side,
A gas inlet is provided in the upper part of the casing, and the gas introduced into the casing from the gas inlet is vented through the hollow fiber from its upper end side to its lower end side. Gas-liquid contact device.   The gas-liquid contact device according to claim 1, wherein an air supply device that supplies gas to the gas introduction port is provided.   3. The gas-liquid contact device according to claim 1, further comprising means for reducing a dew point of the gas supplied to the gas introduction port.   4. The gas-liquid contact device according to claim 1, further comprising a filter for a gas supplied to the gas inlet.   5. The gas-liquid contact device according to claim 1, wherein the liquid is water, and the hollow fiber is formed of a hydrophobic membrane.   6. The gas-liquid contact device according to claim 5, wherein the hollow fiber is made of at least one member selected from the group consisting of polytetrafluoroethylene, polysulfone, polyethylene, and polyvinylidene difluoride.   6. The gas-liquid contact device according to claim 5, wherein the hollow fiber is made of a microfiltration membrane or an ultrafiltration membrane.   The gas-liquid contact device according to any one of claims 5 to 7, wherein a biofilm is formed on an outer surface of the hollow fiber.   9. The gas-liquid contact device according to claim 8, further comprising means for separating the biofilm. A gas-liquid contact method using the gas-liquid contact device according to any one of claims 1 to 9,
The inflow port is formed so that a gas reservoir is formed in an upper portion of the casing, an upper end of the hollow fiber is located in the gas reservoir, and a lower side of the upper end is submerged in the liquid. And a liquid is circulated in the casing through the outlet, the gas is introduced into the upper part of the casing from the gas inlet, and the gas is vented from the upper end side to the lower end side of the hollow fiber. Gas-liquid contact method.   The gas-liquid contact method according to claim 10, wherein the pressure of the gas supplied into the hollow fiber is not less than atmospheric pressure and not more than 1.1 atm.   12. The gas-liquid contact method according to claim 10, wherein a biofilm is formed on the outer surface of the hollow fiber by gas-liquid contact.   The gas-liquid contact method according to claim 12, wherein the biofilm is peeled off when the biofilm grows more than a predetermined amount.   14. The gas-liquid contact method according to claim 13, wherein the biofilm is peeled off by supplying bubbles into the casing or increasing a liquid passing speed in the casing.

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