JP6938875B2 - Biological processing equipment - Google Patents

Description

The present invention relates to an aerobic biological treatment device for organic wastewater.

Since aerobic biological treatment is inexpensive, it is often used as a treatment method for organic wastewater. In this method, it is necessary to dissolve oxygen in the water to be treated, and aeration is usually performed by an air diffuser.

Aeration with an air diffuser has a low dissolution efficiency of about 5-20%. In addition, it is necessary to aerate at a pressure higher than the water pressure applied to the water depth where the air diffuser is installed, and a large amount of air is blown at a high pressure, so that the power cost of the blower is a problem. Usually, more than two-thirds of the electricity costs in aerobic biotreatment are used for oxygen dissolution.

Deep aeration tanks have been widely used as biological treatment equipment in factories and urban areas where the site area is small because the required area of the equipment can be reduced and the oxygen dissolution efficiency is high. However, a deep aeration tank for biological treatment having a water depth of 5 m or more, for example, about 10 m, has a drawback that a high-pressure blower is required when aeration is performed from the bottom, the efficiency of the blower is low, and the power cost is high. In some cases, a general-purpose medium-pressure blower is used to aerate from the middle part of the aeration tank, and the entire tank is agitated and mixed by a swirling flow. However, in this method, the dissolution efficiency of oxygen is lower than that of full aeration, and the power cost is higher.

In the method using a high-voltage blower, the power cost is high because the efficiency of the high-voltage blower is low. In addition, the swirling flow method of a general-purpose blower consumes a large amount of power because the oxygen dissolution efficiency is low.

Membrane aeration bioreactors (MABRs) can dissolve oxygen without the generation of air bubbles. In MABR, since it is sufficient to ventilate air having a pressure lower than the water pressure applied to the water depth, the required pressure of the blower is low and the oxygen dissolution efficiency is high. However, in MABR, since bubbles are not generated, it is difficult to mix and stir the liquid, and as a result, the contact between the microorganism and the substrate is deteriorated, so that the treatment efficiency is lowered.

In order to improve this, aeration is usually performed intermittently (for example, 1 to 5 minutes every 10 to 30 minutes) to mix and stir the liquid to bring the microorganism into contact with the substrate. However, a large blower is needed to aerate. Moreover, since the stirring efficiency of the blower is low, the power consumption is high.

Japanese Unexamined Patent Publication No. 11-162

An object of the present invention is to provide a biological treatment apparatus capable of dissolving a large amount of oxygen in a reaction vessel with low power consumption and having good contact efficiency between wastewater and microorganisms.

The biological treatment apparatus of the present invention is a deep reaction tank type biological treatment apparatus, and supplies an oxygen-containing gas to the reaction vessel, the oxygen permeable membrane module installed in the reaction vessel, and the oxygen permeable membrane module. The oxygen-containing gas supply means and the oxygen permeable membrane module are provided with a non-porous oxygen permeable membrane, which allows oxygen in the supplied oxygen-containing gas to permeate into the tank and in the tank. It is characterized in that no bubbles are generated in the water.

In the biological treatment apparatus of one aspect of the present invention, the reaction vessel has a water depth of 6 m or more.

In the biological treatment apparatus of one aspect of the present invention, the oxygen permeable membrane module is installed in a tank so that at least a part of the membrane has a water depth of 6 m or more.

In the biological treatment apparatus of one aspect of the present invention, the oxygen permeable membrane module is installed in a tank so that the entire membrane has a water depth of 6 m or more.

In the biological treatment apparatus of one aspect of the present invention, the oxygen supply means includes a blower, and the pressure of the blower is smaller than the water pressure generated by the water depth of the reaction vessel.

In the biological treatment apparatus of one aspect of the present invention, the membrane is a hollow fiber membrane, and the oxygen permeable membrane module includes a header in which the ends of the hollow fiber membrane are continuous.

In the biological treatment apparatus of the present invention, since the water depth of the reaction vessel is 6 m or more and the oxygen permeable membrane module is used, oxygen is efficiently dissolved in water by membrane permeation. In the present invention, the blower pressure can be lowered as compared with the case where the oxygen-containing gas is blown into water.

It is a vertical sectional view of the biological processing apparatus which concerns on embodiment. (A) is a side view of the oxygen supply permeable membrane module, and (b) is a perspective view of the oxygen supply permeable membrane module. It is a front view of the hollow fiber membrane module. It is a vertical sectional view of the biological processing apparatus which concerns on embodiment. It is a perspective view explaining the arrangement of the hollow fiber membrane. It is a perspective view explaining the arrangement of the hollow fiber membrane. It is an exploded perspective view of the hollow fiber membrane module. It is a perspective view of the hollow fiber membrane module. (A) is a side view showing the arrangement of hollow fiber membranes in the hollow fiber membrane module, and (b) is a plan view thereof. It is a side view of the hollow fiber membrane module. It is a side view of the hollow fiber membrane module. It is a graph which shows the oxygen dissolution efficiency. It is a graph which shows the summary oxygen transfer coefficient.

Hereinafter, the present invention will be described in more detail with reference to the drawings.

The biological treatment apparatus of the present invention is an aerobic biological treatment apparatus suitable for treating organic wastewater from sewage, paper pulp, chemicals, foods, automobile manufacturing processes, etc., and oxygen permeates into a deep tank type reaction vessel. A membrane module is placed. 1 (a) to 1 (d) are vertical cross-sectional views showing the biological treatment devices 1A to 1D according to an example of the present invention, respectively. Each of the biological treatment devices 1A to 1D includes a plurality of oxygen permeable membrane modules 2 arranged in multiple stages in the upper and lower stages in the deep tank type reaction tank 3. In this embodiment, the oxygen permeable membrane module 2 is installed in three stages, but it is preferable that the oxygen permeable membrane module 2 is installed in 2 to 8 stages, particularly in 2 to 4 stages.

The reaction vessel 3 preferably has a water depth of 6 m or more, for example, 6 to 100 m, particularly 10 to 20 m. It is preferable that at least a part of the oxygen permeable membrane module 2, particularly the upper end of the oxygen permeable membrane module 2, is installed so as to have a water depth of 6 m or more, for example, 10 to 20 m. When a plurality of modules are provided, it is preferable that the upper end of at least one oxygen permeable membrane module 2 is installed so as to have a water depth of 6 m or more, for example, 10 to 20 m.

In the biological treatment devices 1A to 1D, the raw water is supplied to the upper part of the reaction tank 3, and the treated water may be taken out from the lower part of the reaction tank 3, and the raw water is supplied to the lower part of the reaction tank 3 and the reaction tank 3 is used. Treated water may be taken out from the upper part of 3. Raw water may be supplied to the lower part of the reaction vessel 3 by a distributor, and in this way, an upward flow of the plug flow is likely to be formed.

The oxygen permeable membrane module 2 includes a non-porous oxygen permeable membrane, and since the oxygen permeated through the membrane dissolves in the water to be treated in the reaction tank 3, no bubbles are generated in the reaction tank 3.

In FIG. 1A, oxygen-containing gas such as air from the blower B is supplied to the upper part of the oxygen permeable film module 2c at the lowermost stage by the pipe 4, flows out from the lower part of the oxygen permeable film module 2c, and flows through the pipe 5. It is supplied to the upper part of the oxygen permeable film module 2b in the second stage from the top, flows out from the lower part of the oxygen permeable film module 2b, and is supplied to the upper part of the oxygen permeable film module 2a in the uppermost stage via the pipe 6. The gas flowing out from the lower part of the oxygen permeable membrane module 2b is discharged through the pipe 7.

In the biological treatment apparatus of FIG. 1 (b), the oxygen-containing gas from the blower B is supplied to the upper part of the oxygen permeable membrane module 2c at the lowermost stage by the pipe 4, flows out from the lower part, and is two stages from the bottom. It is supplied to the lower part of the oxygen permeable membrane module 2b of the eye, flows out from the upper part thereof, is then supplied to the lower part of the oxygen permeable membrane module 2a in the uppermost stage, and is discharged from the upper part through the pipe 7.

In the biological treatment apparatus of FIG. 1 (c), the oxygen-containing gas from the blower B is supplied to the lower part of the oxygen permeable membrane module 2c at the lowermost stage by the pipe 4, flows out from the upper part thereof, and flows out from the upper part, and is in the second stage from the bottom. It is supplied to the lower part of the oxygen permeable membrane module 2b of the eye, flows out from the upper part thereof, is then supplied to the lower part of the oxygen permeable membrane module 2a in the uppermost stage, and is discharged from the upper part through the pipe 7.

In the biological treatment apparatus of FIG. 1D, the oxygen-containing gas flows in parallel with the oxygen permeable membrane modules 2a to 2c. That is, the oxygen-containing gas from the blower B is supplied to the upper part of each oxygen permeable membrane module 2a, 2b, 2c by the pipe 4, flows out from each lower part, and is discharged through the pipe 7.

As shown in FIGS. 1A and 1B, the oxygen-containing gas is supplied to the upper part of the oxygen permeable membrane module 2c in the lowermost stage, flows out from the lower part of the oxygen permeable membrane module 2c, and then flows out from the lower part of the oxygen permeable membrane module 2c, and then the oxygen permeable membrane on the upper side. In the biological treatment apparatus configured to flow sequentially through the modules 2b and 2a, the condensed water in the oxygen permeable membrane module can easily escape.

When the oxygen-containing gas is configured to flow upward in the oxygen permeable membrane modules 2a to 2c as shown in FIG. 1 (c), the condensed water in the oxygen permeable membrane module is likely to evaporate. In particular, by flowing a highly dry gas as an oxygen-containing gas, the condensed water is likely to evaporate.

As shown in FIGS. 1 (a) to 1 (c), the reaction occurs in a biological treatment apparatus in which the oxygen-containing gas is sequentially circulated from the lowermost oxygen permeable membrane module 2c to the upper oxygen permeable membrane modules 2b and 2a. By making the flow of the water to be treated in the tank 3 an upward flow plug flow, more oxygen is supplied to the water to be treated on the raw water side with a higher BOD concentration, so the oxygen supply amount is set according to the load. be able to.

When the oxygen-containing gas is circulated in parallel with each of the oxygen permeable membrane modules 2a to 2c as shown in FIG. 1D, the pressure loss of the oxygen-containing gas is small and energy saving is achieved. In addition, in FIG. 1D, the oxygen-containing gas flow amount is larger as the oxygen permeable membrane module arranged on the raw water side (for example, when the water to be treated is upward flow, the oxygen permeable membrane module on the lower stage side). By doing so, the oxygen supply amount can be adjusted according to the load.

In any of FIGS. 1 (a) to 1 (d), the membrane area may be made smaller or the membrane filling density may be made lower as the oxygen permeable membrane module on the downstream side in the flow direction of the water to be treated becomes smaller. ..

The oxygen permeable membrane of the oxygen permeable membrane module 2 may be a hollow fiber membrane, a flat membrane, or a spiral membrane, but a hollow fiber membrane is preferable. As the material of the film, silicon, polyethylene, polyimide, polyurethane and the like, which are usually used for MABR, can be used, but silicon is preferable. A composite film in which a porous hollow fiber is coated with a non-porous polymer having high strength may be used.

The hollow fiber membrane preferably has an inner diameter of 0.05 to 4 mm, particularly 0.2 to 1 mm, and a thickness of 0.01 to 0.2 mm, particularly 0.02 to 0.1 mm. If the inner diameter is smaller than this, the ventilation pressure loss is large, and if it is large, the surface area is small and the oxygen dissolution rate is reduced. If the thickness is smaller than the above range, the physical strength becomes small and the material is easily broken. On the contrary, when the thickness is larger than the above range, the oxygen permeation resistance becomes large and the oxygen dissolution efficiency decreases.

The length of the hollow fiber membrane is preferably about 0.5 to 3 m, particularly preferably about 1 to 2 m. If the hollow fiber membrane is too long, when a large amount of biofilm adheres, problems such as breakage, solidification in a dumpling shape, a small surface area, a decrease in oxygen dissolution efficiency, and an increase in pressure loss occur. If the hollow fiber membrane is too short, the cost will be high. The length of the flat film and the spiral film is preferably 0.5 to 1.5 m for the same reason.

FIG. 2 shows an example of the oxygen permeable membrane module 2. The oxygen permeable membrane module 2 uses a hollow fiber membrane 12 as an oxygen permeable membrane. In this embodiment, the hollow fiber membranes 12 are arranged in the vertical direction, the upper end of each hollow fiber membrane 12 is connected to the upper header 10, and the lower end is connected to the lower header 11. The inside of the hollow fiber membrane 12 communicates with the upper header 10 and the lower header 11, respectively. Each of the headers 10 and 11 has a hollow tubular shape, and a plurality of headers 10 and 11 are arranged in parallel in a substantially horizontal direction. Even when a flat film or a spiral film is used, it is arranged in the vertical direction.

It is preferred that one end or both ends of each header 10 is connected to the manifold 13 and one end or both ends of each header 11 is connected to the manifold 14. When the oxygen-containing gas is supplied to the upper part of the oxygen permeable membrane module 2 and discharged from the lower part of the oxygen permeable membrane module 2, the oxygen-containing gas flows from the upper header 10 through the hollow fiber membrane 12 to the lower header 11, during which time. Oxygen permeates the hollow fiber membrane 12 and dissolves in the water in the reaction vessel 3. On the contrary, when the oxygen-containing gas is supplied to the lower part of the oxygen permeable membrane module 2 and discharged from the upper part, the oxygen-containing gas is supplied to the lower header 11 and discharged from the upper header 10 through the hollow fiber membrane 12. ..

FIG. 3 is a front view showing an example of the oxygen permeable membrane module 2 arranged in the frame 15. The frame 15 has four pillars 15a erected at four corners, an upper beam 15b erected between the upper ends of the pillars 15a, and a lower beam erected between the lower portions of the pillars 15b. It has a beam 15c and a bottom plate 15d attached to the lower end surface of each pillar 15a. By holding the manifolds 13 and 14 of the oxygen permeable membrane module 2 in the frame 15, the oxygen permeable membrane module 2 is installed in the frame 15.

The oxygen permeable membrane module 2 provided with the frame 15 can be easily installed in the reaction tank 3 in multiple stages up and down. That is, the upper oxygen permeable membrane module 2 can be arranged so that the bottom plate 15d of the upper oxygen permeable membrane module 2 is placed on the frame 15 of the lower oxygen permeable membrane module 2.

In one aspect of the present invention, a hollow fiber membrane module in which hollow fiber membranes are arranged in the vertical direction is made into a low-height membrane module having a height of about 1 to 2 m, and these are laminated in two or more stages, preferably four or more stages. do.

By stacking the hollow fiber membrane modules having a short length and a low height in multiple stages in this way, oxygen can be dissolved at a low pressure.

The pressure of the oxygen-containing gas blown to the hollow fiber membrane is preferably slightly higher than the pressure loss of the hollow fiber membrane, for example, about 5 to 20% higher from the viewpoint of cost.

The pressure supplied to the hollow fiber membrane may be determined regardless of the water depth. Since a normal air diffuser requires a pressure higher than the water depth, the present invention is more advantageous as the water depth in the reaction vessel is deeper.

It should be noted that the influence of the condensed water in the membrane and the carbon dioxide gas dissolved in the membrane from the biological tank differs depending on the pipe connection of the module in the vertical direction. Therefore, it is preferable to have a pipe connection structure in consideration of pressure loss, condensed water, and carbon dioxide gas.

In the present invention, as shown in FIG. 4, a partition 20 in the vertical direction is provided in the reaction tank 3, a downward flow portion 21 and an upward flow portion 22 are provided in the reaction tank 3, and the downward flow portion 21 and the upward flow portion 21 are provided. An oxygen permeable membrane module may be installed in each of the flow portions 22. In FIG. 4, the oxygen permeable membrane modules 2a to 2c and 2d to 2f are installed in three stages in the downward flow portion 21 and the upward flow portion 22, respectively, but the number of installation stages is not limited to this.

The oxygen-containing gas from the blower B is sequentially circulated from the uppermost oxygen permeable membrane module 2a in the descending flow portion 21 to the oxygen permeable membrane modules 2b and 2c via the pipes 4, 4a and 4b, and the oxygen permeable membrane module 2c. Outflow gas is supplied to the lowermost oxygen permeation film module 2d in the upward flow portion 22 via the pipe 4c. Then, the oxygen permeable membrane modules 2e and 2f are sequentially circulated through the pipes 4d and 4e, and the outflow gas of the uppermost oxygen permeable membrane module 2f is discharged from the pipe 7. The raw water is supplied to the upper part of the downward flow part 21, descends in the downward flow part 21, goes around the lower end of the partition 20 and rises in the upward flow part 22, and is treated water from the upper part of the upward flow part 22. Is taken out.

In FIG. 4, the oxygen permeable membrane modules 2a to 2f in the descending flow portion 21 and the upward flow portion 22 are connected in series, and the oxygen-containing gas is circulated through the oxygen permeable membrane modules 2a to 2f by one blower B. However, the oxygen-containing gas may be circulated from separate blowers to the oxygen permeable membrane modules 2a to 2c of the downward flow portion 21 and the oxygen permeable membrane modules 2d to 2f of the upward flow portion 22.

In FIG. 4, the lower end of the partition 20 is higher than the bottom surface of the reaction tank 3, and the upper end of the partition 20 is projected upward from the water surface in the reaction tank 3, but conversely, the lower end of the partition 20 is the reaction tank 3. The upper end of the partition 20 may be lower than the water level of the reaction tank 3 so as to be in contact with the bottom surface of the reaction tank 3.

In this case, the raw water is supplied to the lower part of the upward flow part, rises in the upward flow part, then wraps around the upper side of the partition and flows into the downward flow part, descends in the downward flow part, and lowers the lower part of the downward flow part. Treated water is taken out from.

Although not shown, a plurality of upward flow portions and downward flow portions are provided in the reaction tank 3, and the raw water is discharged from the downward flow portion → the upward flow portion → the downward flow portion → the upward flow portion or the upward flow portion →. The flow path may be lengthened by allowing the flow to flow in the order of a downward flow portion → an upward flow portion → a downward flow portion.

In the present invention, it is preferable that the raw water is passed in an upward flow or a downward flow to form a plug flow. Efficient biological treatment is possible by bringing the liquid into contact with the living organism using the flow of the plug flow. When raw water is supplied through a distributor, a plug flow is easily formed.

In normal aerobic biological treatment, it was not possible to form an upflow or downflow plug flow due to aeration. However, since no bubbles are generated in MABR, there is no turbulence between the upper and lower liquids, and an upward flow or a downward flow plug flow is easily formed.

The LV of the water to be treated in the reaction vessel 3 is preferably 4 m / hr or more, for example, 4 to 40 m / hr, regardless of the BOD concentration of the raw water, and when it is 8 m / hr or more, sufficient substrate and microorganisms are mixed. ..

In the above embodiment, as shown in FIGS. 2 and 3, the hollow fiber membrane 12 is oriented in the vertical direction, and the raw water (water to be treated) flows in the vertical direction along the hollow fiber membrane 12, but at least a part thereof. As the oxygen permeable membrane module, an oxygen permeable membrane module having a hollow fiber membrane 12a arranged in the horizontal X direction as shown in FIG. 5 and a hollow fiber membrane 12b arranged in the horizontal Y direction orthogonal to the hollow fiber membrane 12a is used. You may. In this case, in order to prevent sludge and the like from accumulating on the upper surface side of the hollow fiber membranes 12a and 12b, it is preferable that the raw water is passed in an upward flow.

FIG. 6 is a perspective view showing an example of an oxygen permeable membrane module provided with the hollow fiber membranes 12 (12a, 12b) in the X and Y directions. The oxygen permeable membrane module 30A comprises a pair of parallel headers 31 and 31 extending in the Y direction, a pair of headers 32 and 32 extending in the X direction orthogonal to the pair of headers 31 and 31, and a hollow fiber membrane 12. Have. The hollow fiber membrane 12a in the X direction is erected between the headers 31 and 31, and the hollow fiber membrane 12b in the Y direction is erected between the headers 32 and 32. The inside of the hollow fiber membrane 12a communicates with the inside of the header 31, and the inside of the hollow fiber membrane 12b communicates with the inside of the header 32.

By connecting the ends of the headers 31 and 32 to each other, the headers 31 and 32 have a square frame shape, but closing members (not shown) such as end plugs are provided inside both ends of the headers 31 and 32. The headers 31 and 32 are blocked. The oxygen-containing gas is supplied to one header 31, passes through the hollow fiber membrane 12a, and flows into the other header 31. Further, the oxygen-containing gas is supplied to one header 32, passes through the hollow fiber membrane 12b, and flows into the other header 32.

In FIG. 6, the hollow fiber membranes 12a and 12b are simply overlapped as shown in FIG. 5, but as shown in FIGS. 7A and 7B, the hollow fiber membranes 12a in the X direction and the hollow fibers in the Y direction are formed. The film 12b may be braided in a plain weave shape.

In FIG. 6, the oxygen permeable membrane module 30A includes hollow fiber membranes 12a and 12b extending in two orthogonal directions, but as shown in FIG. 8, the hollow fiber membranes 12 extending in parallel in only one direction are 1 An oxygen permeable membrane module 30 which is erected between a pair of headers 33 and 33 and whose both ends of the headers 33 and 33 are connected by a rod-shaped connecting member 34 to form a square frame may be used.

In this case, a plurality of oxygen permeable membrane modules 30 are stacked and arranged in the reaction vessel so that the directions of the hollow fiber membranes 12 are alternately reversed. In FIG. 8, in the oxygen permeable membrane module 30 of the odd-numbered stages (top and third stages from the top), the hollow fiber membrane 12 extends in the Y direction, and the oxygen permeable membrane module of the even-numbered stage (second stage) In No. 30, the hollow fiber membrane 12 extends in the X direction. In FIG. 8, only three stages of the oxygen permeable membrane module 30 are shown, but two or four or more stages may be installed. Further, although the oxygen permeable membrane modules 30 are separated from each other in FIG. 8, they are actually arranged closer to each other than shown in the drawing so as to be overlapped with each other, for example.

As shown in FIGS. 9 and 10, a plurality of oxygen permeable membrane modules 30 may be arranged in the frame 15 to form a unit. In FIG. 9, an oxygen permeable membrane module 30 having a hollow fiber membrane in the X direction (hereinafter referred to as an oxygen permeable membrane module 30X) and an oxygen permeable membrane module 30 having the hollow fiber membrane in the Y direction are contained in one frame 15. (Hereinafter referred to as oxygen permeation membrane module 30Y) are alternately arranged in multiple stages.

In FIG. 10, a unit in which the oxygen permeable membrane module 30X is arranged in the frame 15 and a unit in which the oxygen permeable membrane module 30Y is arranged in the frame 15 are arranged so as to be stacked vertically. In FIG. 10, only two stages of the unit are shown, but three or more stages may be provided.
Although each of these hollow fiber membranes is one in FIGS. 5 to 8, it may be a bundle of several to 100 hollow fiber membranes.

By arranging the hollow fiber membranes horizontally and in a mesh or lattice pattern, the water to be treated rising from the bottom is agitated and mixed as it passes through the mesh or lattice, and comes into contact with the microorganisms adhering to the hollow fiber membranes. .. As the water to be treated rises, and each time it passes through a mesh or lattice, the water to be treated comes into contact with microorganisms and biological treatment proceeds. The same applies when descending from the upper part.

When the hollow fiber membrane is arranged only in the vertical direction, the hollow fibers are bundled into a large bundle to form a water passage through which water preferentially passes, and a short pass is likely to occur.

By arranging the hollow fiber membranes horizontally and in a mesh pattern, it is possible to prevent the hollow fiber membranes from being agglomerated by the slime of the grown microorganisms, and the contact efficiency is improved.

In the present invention, a reaction tank in which the water to be treated flows sideways may be further provided. In this case, in order to make the flow of the water to be treated a plug flow, it is preferable to make the reaction tank elongated and set the length-to-horizontal length ratio to 20: 1 or more. In this case, the lateral linear velocity of the water to be treated is preferably 4 m / hr or more, as in the case of upward flow and downward flow.

When the water to be treated is flowed sideways in this way, as at least a part of the oxygen permeable membrane modules, the hollow fiber membranes 12c in the vertical direction and the hollow fiber membranes 12d in the horizontal direction are arranged in a grid pattern as shown in FIG. It may be configured so that the raw water flows horizontally through the lattice. A mesh-shaped hollow fiber membrane module may be used instead of the grid-like shape.

Next, preferable examples of the oxygen-containing gas, blower, etc. used in the present invention will be described.

<Oxygen-containing gas>
The oxygen-containing gas may be a gas containing oxygen such as air, oxygen-enriched air, and pure oxygen. It is desirable that the aerated gas is passed through a filter to remove fine particles.

The amount of aeration is preferably about twice as much as the amount of oxygen required for the biological reaction. If it is less than this, BOD and ammonia remain in the treated water due to lack of oxygen, and if it is more than this, the air volume becomes unnecessarily large and the pressure loss becomes high, which impairs economic efficiency.

It is desirable that the aeration pressure is slightly higher than the pressure loss of the hollow fiber generated at a predetermined aeration amount.

<Blower>
It is sufficient for the blower to have a discharge air pressure equal to or less than the water pressure coming from the water depth. However, it is necessary that the pressure loss is greater than or equal to the pressure loss of piping or the like. Usually, the piping resistance is about 1 to 2 kPa.

In the case of a water depth of 5 m, a general-purpose blower having an output of up to about 0.55 MPa is usually used, and in a water depth of more than that, a high-pressure blower has been used.

In the present invention, a general-purpose blower having a pressure of 0.5 MPa or less can be used even at a water depth of 5 m or more, and it is preferable to use a low pressure blower of 0.1 MPa or less.

The supply pressure of the oxygen-containing gas is higher than the pressure loss of the hollow fiber membrane and lower than the water depth pressure, and the membrane is not crushed by the water pressure. Since the pressure loss of the flat film and the spiral film is negligible as compared with the water pressure, the pressure is extremely low, about 5 kPa or more, water pressure or less, and preferably 20 kPa or less.

In the case of a hollow fiber membrane, the pressure loss changes depending on the inner diameter and length. Since the amount of air to be aerated is ²⁰ mL to 100 mL / day per 1 m 2 of the membrane, the amount of air doubles when the membrane length doubles, and even if the membrane diameter doubles, the amount of air only doubles. It doesn't become. Therefore, the pressure loss of the membrane is directly proportional to the membrane length and inversely proportional to the diameter.

The value of the pressure loss is about 3 to 20 kPa for a hollow yarn having an inner diameter of 50 μm and a length of 2 m.

According to the experiment of the present inventor, as a result of changing the aeration pressure from 11 to 140 kPa and the aeration amount from 240 to 460 mL / min, it was confirmed that the oxygen dissolution rate hardly changed.

In the present invention, it is preferable that the oxygen dissolution efficiency is 30 to 100%, particularly 40 to 60%.

In FIG. 12, a hollow fiber membrane module having a membrane area of 1.5 m ² and a supply capacity of 12 g-O ₂ / m ² / day is used, and air is supplied at 70 mL / min and 11 to 140 mBar. It is a graph which shows an example of the oxygen dissolution efficiency at the time of operation with the dissolution efficiency of 60%. The curve between 1/11 and 1/31 in FIG. 12 is due to the consumption of oxygen by the adhesion of the biofilm to the hollow fiber membrane. Variations in oxygen dissolution efficiency are caused by consumption by biofilms and fluctuations in BOD (COD) loading.

If the oxygen concentration at the inlet of the hollow fiber membrane is 20% (in the air) and the oxygen concentration at the outlet is 10% (decreased by penetrating the membrane), the oxygen dissolution efficiency is 50%. Increasing the air volume supplies a sufficient amount of oxygen and reduces the dissolution efficiency. On the contrary, when the air volume is lowered, oxygen is completely permeated at the inlet portion, and the dissolution efficiency approaches 100%.

When setting the specifications of the biological treatment apparatus of the present invention, it is preferable to determine the water depth and the blower pressure, then determine the dissolution efficiency, determine the membrane area corresponding thereto, and determine the air volume. The determination of membrane area and air volume may be reversed.

In addition, it is generally preferable that kLa (total oxygen transfer coefficient) is high, but when an oxygen permeable membrane is used, even if the pressure is increased, the performance of the membrane is not exceeded. Therefore, it is necessary to change the air volume to control the dissolution amount or increase the membrane area.

The upper graph of FIG. 13 shows kLa when the hollow fiber membrane module is installed in a water tank having a water depth of 60 cm (hollow fiber membranes of substantially the same length are arranged vertically) and the oxygen supply pressure is changed. The lower graph of 13 shows kLa when a hollow fiber membrane module in which a 60 cm hollow fiber membrane is vertically arranged is installed in a water tank having a water depth of 5 m and the oxygen supply pressure is changed.

In both cases, oxygen is permeated even at a pressure lower than the water depth, so a blower supplied at a pressure lower than the water pressure can be used.

In addition, kLa hardly changes depending on the water depth.

The straight line connecting (1) in FIG. 13 is a theoretical line when the air diffuser is used, and indicates that kLa depends on the air volume and pressure. Therefore, bubbles do not come out from the air diffuser into the tank unless a pressure higher than the deep water pressure is applied.

In the case of deep aeration with a water depth of 5 m or more, it was necessary to use a high-pressure blower in a normal air diffuser that generates air bubbles, but due to the influence of pressure loss (air leakage, etc.) at that time, the water depth is shallow. Compared with, the required pressure / water pressure gradient becomes larger.

Therefore, by using a non-porous oxygen permeable membrane, it is possible to supply sufficient oxygen into the tank by using a low-pressure blower or a general-purpose blower even for deep aeration of 10 to 20 m or more. Is.

1A ~ 1E Biological processing equipment 2,30,30A Oxygen permeable membrane module 10,11,31,32,33 Header 12,12a ~ 12d Hollow fiber membrane 13,14 Manifold 15 Frame 20 Partition 21 Downflow part 22 Upward flow part 34 Connecting member

Claims (2)

It is a deep reaction tank type biological treatment device that treats organic wastewater.
A reaction tank to which organic wastewater is supplied and
The oxygen permeable membrane module installed in the reaction vessel and
An oxygen-containing gas supply means for supplying the oxygen-containing gas to the oxygen-containing membrane module, and
With
The oxygen permeable membrane module includes a non-porous oxygen permeable membrane, which allows oxygen in the supplied oxygen-containing gas to permeate into the tank and does not generate bubbles in the tank.
The reaction tank has a water depth of 6 m or more and has a water depth of 6 m or more.
The oxygen permeable membrane module is installed in a tank so that at least a part of the membrane has a water depth of 6 m or more.
The oxygen-containing gas that did not permeate the oxygen permeable membrane is discharged to the outside of the reaction vessel via the pipe, and is discharged to the outside of the reaction vessel .
The membrane is a hollow fiber membrane, and the oxygen permeable membrane module includes a header in which the ends of the hollow fiber membrane are connected.
The oxygen supply means includes a blower, and the pressure of the blower is smaller than the water pressure generated by the water depth of the reaction vessel and 5 to 20% higher than the pressure loss of the hollow fiber membrane. A characteristic biological treatment device. The biological treatment apparatus according to claim 1, wherein the oxygen permeable membrane module is installed in a tank so that the entire membrane has a water depth of 6 m or more.

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