JP2008194582A - Wastewater treatment method by foam centrifugation of food wastewater - Google Patents

Abstract

[PROBLEMS] To separate a predetermined substance in waste water discharged during food production, etc., into a concentrated phase and a diluted phase with less power consumption, and to stream as necessary without adding chemicals as much as possible. Provided is a wastewater treatment method capable of purifying wastewater before it can flow. Further, the present invention provides a wastewater treatment method in which the concentrated phase can be returned to the process for resource recycling. Furthermore, the present invention provides a wastewater treatment method capable of efficiently treating a large amount of wastewater without requiring a large capital investment and a large operation cost.
Microbubbles are generated in the drainage, and a substance that can adhere to the surface of the bubbles in the drainage is attached to the surface of the microbubbles and captured. The aggregate of the microbubbles is taken out and centrifuged, and the bubbles are collected. A wastewater treatment method from a food production process for concentrating substances adhering to the surface and purifying the wastewater.
[Selection figure] None

Description

  The present invention relates to a wastewater treatment method for purifying food wastewater with less power consumption and performing as little as possible addition of chemicals from the outside.

  Some effluents during food production contain proteins, sugars, and the like. These substances are dissolved or suspended in the waste water. On the other hand, as a method for separating suspended substances such as proteins, there are an ultrafiltration method, an evaporation drying method, and the like. However, these methods require a large amount of equipment and energy to be adopted as a general process for food production, and are too costly. It is not practical as wastewater treatment during food production. In addition, a method for aggregating and precipitating dissolved substances in waste water by adding a chemical is widely performed.

  On the other hand, active efforts for environmental conservation have been demanded recently. Therefore, it is desired to develop a treatment system that purifies water to a very high level even if it is a food wastewater with a relatively small environmental load. In this case, it is not preferable that the chemical used for the treatment is mixed even in a small amount in the waste water after the purification treatment. Especially in areas where the total organic carbon (TOC) concentration is reduced and, for example, COD (chemical oxygen demand) and BOD (biological oxygen demand) are subject to strict nature protection and environmental pollution prevention standards. However, it is ideal to construct a system for treating wastewater so that it can be adapted. However, as described above, it is difficult for the conventional method to satisfy such strict standards for drainage, and no treatment system that satisfies this has been proposed in practice.

Examples of food wastewater include soybean whey wastewater discharged in tofu production. Soy whey is a liquid component separated from tofu after adding bittern to soy milk and solidifying it, and it contains protein and sugar derived from soybeans.
In relation to this, a method of reusing soybean whey as a carbonated beverage (Patent Document 1) and a method of adding a coagulant and processing it into cotton tofu (Patent Document 2) have been proposed. It is necessary to add drugs. In addition, there is an example in which a predetermined substance is separated using centrifugal separation in tofu production (Patent Documents 3 to 6), but large-scale equipment and enormous energy are required to process the entire amount of wastewater by centrifugation. It becomes. Similar to the ultrafiltration described above, it is not practical as a wastewater treatment method.

Japanese Patent Laid-Open No. 50-064465 Japanese Patent Laid-Open No. 04-218354 Japanese Patent Laid-Open No. 52-130942 JP-A-53-121993 JP 59-203462 A Japanese Patent Laid-Open No. 04-187695

  The present invention separates a predetermined substance in waste water discharged at the time of food production etc. into a concentrated phase and a diluted phase with less power consumption, and if necessary, without adding chemicals etc. It aims at providing the waste water treatment method which can purify | clean waste water before it can be made to flow. It is another object of the present invention to provide a wastewater treatment method in which the concentrated phase can be returned to the process and recycled. It is another object of the present invention to provide a wastewater treatment method that can efficiently treat a large amount of wastewater without requiring a large capital investment and a large operating cost.

(1) Microbubbles are generated in the drainage, and a substance capable of adhering to the surface of the bubbles in the drainage is attached to and captured on the surface of the microbubbles. The aggregate of the microbubbles is taken out and centrifuged, and the surface of the bubbles A method for treating wastewater from a food production process, wherein the substance adhering to the water is concentrated and the wastewater is purified.
(2) The wastewater treatment method according to (1), wherein the substance that can adhere to the bubble surface is a protein.
(3) The wastewater treatment method according to (1), wherein the substance that can adhere to the bubble surface is a carbohydrate.
(4) The waste water treatment method according to any one of (1) to (3), wherein the waste water is soybean whey-containing water discharged during the production of tofu.
(5) The centrifugal separation separates a phase in which the substance capable of adhering to the bubble surface is concentrated as a foam layer and a phase in which the substance capable of adhering to the bubble surface is diluted as a liquid layer (1) The wastewater treatment method according to any one of (4) to (4).

According to the wastewater treatment method of the present invention, with a small amount of power consumption, the predetermined substance in the wastewater can be separated into a concentrated phase and a diluted phase, and the wastewater can be purified without adding chemicals as much as possible. Even if it is a clear stream in a region where strict environmental pollution prevention standards are imposed, it has an excellent effect that it can be purified as needed. Further, if necessary, the concentrated phase can be returned to the food production process for reuse, and resource recycling can be realized.
Furthermore, the wastewater treatment method of the present invention is suitable for the treatment of wastewater from the food production process, and does not require a large facility investment or a large operation cost, and efficiently treats a large amount of wastewater.

Hereinafter, the present invention will be described in detail.
The wastewater treatment method of the present invention includes (i) a step of generating a large number of microbubbles in the wastewater and collecting the microbubbles, and (ii) a phase in which the bubble aggregate is taken out and centrifuged to dilute a predetermined substance. And separating the material into a concentrated phase. This makes it possible to purify wastewater at the time of food production, etc., and preferably to such a degree that it can be flowed into clear streams in areas where strict environmental protection standards are imposed.

First, the step (i) of forming the bubble aggregate will be described with reference to FIG.
FIG. 1 is an apparatus diagram schematically showing a preferred embodiment of an apparatus used in the wastewater treatment method of the present invention (however, the present invention is not construed as being limited by this embodiment). In this step, first, waste water 18 discharged during food production or the like is stored in the bubble column 2. The bubble column 2 is preferably a cylindrical bubble column having a length as shown in the figure. The size of the bubble column is not particularly limited, but when processing soy whey in the industrial production of tofu, for example, the height of the bubble column 2 is preferably 500 to 3000 mm, more preferably 1000 to 2000 mm. The cross-sectional diameter of the bubble column 2 is preferably 50 to 150 mm, more preferably 75 to 100 mm. If the diameter of the bubble column is too large, the flow of bubble aggregates may convect and the floating separation effect may not be obtained. Here, it is preferable that the bubble column 2 is installed with its longitudinal direction set to the vertical direction and sealed by the top 19. In this sealed state, the microbubbles 17 described later can be effectively gathered to form a good bubble aggregate layer 12 and the transfer efficiency to the centrifuge main body 16 can be increased.

The amount of the drainage 18 charged into the bubble column 2 is not particularly limited, but when using a vertically long cylindrical bubble column as shown, for example, the drainage is charged to a height of 1/5 to 2/3 of the height of the bubble column. Is preferable, and 1/4 to 2/3 is more preferable. The drainage 18 is circulated by the liquid feeding pipe 4. Specifically, the drainage 18 is sent through the pipe 4 by the liquid feed pump 3 in the circulation direction p, and returned to the bubble column 2 through the venturi-shaped microbubble generating means 1. At this time, the circulated waste water and the air sent in the separate pipe 27 in the air flow direction q by the compressor 9 are mixed in the micro-bubble generating means 1, so that the inside of the bubble column 2 is good. Bubbles 17 can be generated. The generated microbubbles 17 pass through the liquid layer 11 in the bubble column 2 and gradually gather on the drainage surface (drainage / foam interface) 13 to form the bubble aggregate layer 12 (however, the interface 13 is It doesn't have to be as clear as the one shown.) Furthermore, if the above-mentioned drainage circulation and mixing with air are performed and the microbubbles are continuously sent from the microbubble generating means 1, the bubble aggregate layer 12 increases in height and approaches the top 19 of the bubble column 2. . The temperature at which the bubble aggregate is formed is not particularly limited. For example, the temperature is preferably 10 to 80 ° C, and more preferably 20 to 70 ° C.
Here, it is preferable to provide a flow meter 5, a pressure gauge 6, a valve 8, and the like as necessary in the pipe 4 for drainage circulation and the pipe 27 for sending air.

  Here, the microbubble generating means 1 will be described in detail. The microbubble generating means 1 is not particularly limited as long as the circulated waste water and air can be mixed to generate microbubbles in the bubble column. For example, as described in JP-A-2003-230824, (a) a liquid introduction part for introducing a liquid, (b) a gas introduction part for mixing a gas into the introduced liquid, and (c) a mixed gas And (d) a discharge port for a large number of generated microbubbles, and (e) the liquid contains a surfactant, It is possible to use a device capable of releasing the microbubbles while suppressing coalescence of a large number of microbubbles generated by the microbubble generating unit by the action.

  FIG. 2 is an enlarged cross-sectional view schematically showing a preferred embodiment of the microbubble generator 1. The illustrated microbubble generating means includes a nozzle body 101 and a divergent nozzle portion 102 connected to the nozzle body 101 so as to be in fluid communication therewith. The nozzle main body 101 has a substantially cylindrical shape, and the space surrounded by the inner wall of the nozzle main body preferably has a cylindrical shape. The front end side of the nozzle body 101 has an opening shape and is connected to the divergent nozzle 102. A drain circulation pipe 4 is connected to the base end side of the nozzle body 101. A gas circulation pipe 27 for introducing gas is inserted through the bottom of the nozzle body 101.

  The illustrated divergent nozzle 102 is a nozzle that gradually increases after the cross-sectional area first decreases in the flow direction, and has a shape similar to a Venturi tube. The divergent nozzle 102 has a proximal end portion 108 that is connected to an opening portion on the distal end side of the nozzle body 101 so that fluid communication is possible, and a distal end portion 109 that constitutes a discharge port that discharges the gas-liquid mixed fluid. A narrowed portion with a reduced flow cross-sectional area is formed at the base end portion 108 of the divergent nozzle 102. When the throat 110 formed by the narrowed portion is passed, the inner wall diameter continuously increases. A space surrounded by the inner wall of the divergent nozzle 102, preferably a substantially conical space, generates good microbubbles.

In the side view, the substantially conical space 111 is practically less than 40 °, preferably 20 ° or less, more preferably 10 ° or less, and about 6 °. It is particularly preferable to do this. If the divergence angle θ is too large, flow separation may occur in the vicinity of the discharge port, and resistance to the flow may increase. As a result, it is necessary to increase the pressure at the inlet of the nozzle, and power is used excessively. That is, it is preferable in that the energy saving property is excellent by narrowing the spread angle θ. In the divergent nozzle 102 of the illustrated embodiment, the inner wall of the inner space 111 is linear in side view (or sectional view), that is, the shape of the inner space is conical, but for example, in side view (or sectional view) The inner wall may be formed to have a gently curved surface.
The diameter (throat hole diameter) φ of the narrowest hole of the throat portion 110 is not particularly limited. For example, considering the workability, it is practical to set it to 1 mm or more. The upper limit is not particularly limited, and may be determined by, for example, the amount of wastewater to be treated. Usually, it is practical to use one having a size of about 100 mm or less. It may be a thing.
The flow rate Vp (circulation direction p) of the waste water is not particularly limited, but the flow rate passing through the throat portion is preferably about 9 to 20 m / s. The air flow rate Vq (air flow direction q) is not particularly limited, but is preferably about 1 to 50% as a volume ratio to water.
As described above, the divergence angle θ, the throat hole diameter φ, the drainage flow rate Vp, and the airflow rate Vq are not particularly limited as long as they are appropriately determined depending on the amount of wastewater to be treated. By making it into the range, it is possible to generate and send many better microbubbles one after another as the microbubbles 17. The size of the microbubbles is not particularly limited, but the diameter is preferably a micrometer size, and the average diameter is preferably about 10 to 500 μm.

  The drainage circulation pipe 4 is fluidly connected to the bubble column 2 via the pump 3 (see FIG. 1), and it is preferable that pressurized wastewater is introduced into the nozzle 101. The gas introduction pipe 27 for introducing gas preferably penetrates the bottom wall of the nozzle body 101 and extends parallel to the length direction (fluid flow direction) of the nozzle body 101, and passes through the throat 110. It is preferable to extend on the virtual axis 113. By doing so, the air outlet 114 at the distal end of the gas introduction tube 27 can face the opening of the proximal end portion 108 of the divergent nozzle 102, and the generation of good microbubbles can be promoted.

  Although the nozzle main body 101 and the divergent nozzle 102 are configured by separate members and connected by a frame body 117, they may be configured by a single integrated member. In the illustrated embodiment, the microbubble generator 1 (nozzle body 101, divergent nozzle 102, frame body 117) is joined to the bubble column 2 by the attachment 118. The constituent member of the nozzle body 101 is preferably made of metal (for example, stainless steel), and the constituent member of the divergent nozzle 102 is preferably made of plastic (for example, acrylic resin). However, these materials are not limited.

  The wastewater used in the wastewater treatment method of the present invention is preferably wastewater discharged during food production and contains a substance that can adhere to microbubbles. Examples of substances that can adhere to the microbubbles include suspended substances in liquid (SS). The suspended substances include not only organic compounds but also solids of inorganic compounds and complex compounds thereof. Among them, proteins, carbohydrates, lipids, food fine powders (for example, those having an average particle size of 10 μm or less) and the like that are discharged during food production can be mentioned.

  For example, soybean whey discharged during the production of tofu contains solids of protein and carbohydrates. Usually, water-soluble components are dissolved in water and water-insoluble components are suspended and dispersed in water. Yes. Similar wastewater is also discharged during the manufacture of dairy products. Rice soup also contains carbohydrates. In the wastewater treatment method of the present invention, the above-mentioned wastewater can be purified, and wastewater containing solids is preferably treated, and soy whey discharged during tofu production is more preferred. The content of solids contained in soy whey varies depending on the type and amount of tofu to be produced, but soy whey containing 10% to 15% solids is common.

  When soybean whey is treated by the wastewater treatment method of the present invention, the wastewater may be stored immediately after production (immediately after discharge) or stored for a certain period thereafter. Proteins, etc. contained in soy whey may be altered by storage, but according to the wastewater treatment method of the present invention, solids etc. are effectively concentrated even when the state of wastewater changes as such. Phase and diluted phase can be separated, and good treatment can be performed. The waste water may contain an additive such as a pH adjuster. For example, an additive may be appropriately added to control the formation of the above-described microbubble aggregate.

  In the wastewater treatment method of the present invention, at least a part of the microbubble aggregate formed in the bubble column 2 as described above is taken out and centrifuged. This process will be described with reference to FIG. 1 (however, the present invention is not construed as being limited by this embodiment). The microbubble aggregate 12 formed in the bubble column 2 is taken out gradually in the suction direction r through the suction pipe 15 by a suction pump (not shown). At this time, the suction tube 15 is connected to the centrifuge main body 16, and the centrifuge main body 16 is further connected to the collection container 32. Thus, it is preferable that the microbubble aggregate 12 flows over the entire foam centrifuge system (the suction tube 15, the centrifuge main body 16, and the collection container 32).

  In this foam centrifuge system, each member may be connected by a normal connector. Here, the centrifuge main body 16 has a shaft rod 27. The shaft rod 27 is rotatably installed on the support column 23, and the shaft rod 27 is connected to a rotary drive (not shown). The centrifuge main body 16 is rotated by this rotary drive (motor or the like). In the foam centrifuge system shown in the figure, the support column 23 and the collection container 32 are installed and fixed on the substrate 28.

  The bubble aggregate taken out by the suction tube 15 is sent to the centrifuge main body 16. The centrifuge body can rotate in the rotation direction t or u to centrifuge the bubble aggregate inside. At this time, the bubble aggregate inside the centrifuge body 16 is gradually moved toward the moving direction s by the pushing force of the bubble aggregate flowing in later, and is moved to the bottom of the collection container 32 while being centrifuged. It is collected. In the collection container 32, the post-centrifugation foam layer 24 in which the substance that can adhere to the surface of the microbubbles contained in the drainage 18 is concentrated, and the post-centrifugal liquid in which the substance that can adhere to the surface of the microbubbles is diluted. Separated into layer 26 and collected. The temperature at the time of centrifugation is not specifically limited, For example, it is preferable to carry out at 10-80 degreeC, and 20-70 degreeC is more preferable.

  The size of the centrifuge main body 16 is not particularly limited and may be appropriately selected depending on the amount of wastewater to be treated. However, when considering the treatment in the industrial production of soybean whey, for example, a diameter of 100 to 300 mm is preferable, and 150 to 200 mm is more preferable. The length is preferably 150 to 500 mm, more preferably 200 to 400 mm. The centrifugal force due to the rotation of the centrifuge body is not particularly limited and can be adjusted as appropriate according to the type and concentration of the wastewater to be treated. For example, the centrifugal force can be rotated to 2 to 20 G. preferable.

  Since the post-centrifugation foam layer 24 and the post-centrifugation liquid layer 26 collected in the collection container 32 are separated into two layers as shown in the figure, each is easily separated and recovered. be able to.

  Regarding the concentration of the substance that can adhere to the bubble surface, the substance that can adhere to the bubble surface may be concentrated in the bubble assembly 12 before the centrifugal separation, compared to the drainage 18. If it is taken out, it does not need to be concentrated.

  And it is practical that the concentration rate after the centrifugation of the substance which can adhere to the bubble surface in the concentration foam 24 is the concentration rate of 3 times or less, and it has a practical advantage in the range. On the other hand, the post-centrifugation dilution rate of the substance that can adhere to the bubble surface in the diluted liquid 26 is practically a dilution rate of 0.3 or more, and usually has practical advantages in that range. Here, the concentration ratio after centrifugation is defined as a value obtained by dividing “mass concentration of TOC of foam 24 after centrifugation” by “mass concentration of TOC of waste water 18 charged in the bubble column”. The dilution ratio after centrifugation is defined as a value obtained by dividing “mass concentration of TOC of liquid 26 after centrifugation” by “mass concentration of TOC of waste water 18 charged in the bubble column”.

  Thus, according to the wastewater treatment method of the present invention, the concentrated foam 24 obtained by concentrating suspended solids (SS) and the like and the diluted liquid 26 obtained by diluting the concentrated foam 24 can be separated and easily recovered. As a result, the diluted liquid 26 can be drained as wastewater that has been purified by diluting the TOC concentration by a wastewater purification process such as a septic tank. The above-mentioned concentrated foam 24 may be used for, for example, organic fertilizer, compost or feed, and may be recycled after returning to the manufacturing process if it can be used for food production. In this case, the concentrated foam 24 liquefies with time, but an antifoaming agent may be added to promote liquefaction.

  The present invention will be described in more detail based on examples, but the present invention should not be construed as being limited thereby.

The apparatus shown in FIG. 1 was used to treat soybean whey wastewater as follows.
A soybean whey waste water 18 having a temperature of 58 ° C. and a pH of 5.6 was charged into a bubble column 2 (a cylindrical bubble column having a diameter of 100 mm and a height of 1500 mm). Then, the whey drainage is circulated through the pipe 4, mixed with the air sent from the other pipe 27 by the venturi-shaped microbubble generating means 1 (expansion angle θ: 6 °, throat hole diameter φ: 3 mm), and supplied to the bubble column 2. did. At this time, the circulation flow rate Vp of the whey drainage was set to 6.7 [L / min], and the air flow rate Vq was set to 0.6 [L / min]. About 10 minutes after the start of the experiment, the bubble aggregate started to move to the foam centrifuge body 16 (a horizontal type having a diameter of 140 mm and a length of 300 mm was used, and the centrifugal force was 6 G).

Subsequently, the bubble aggregate 12 in the bubble column has moved continuously through the suction tube 15 to the foam centrifuge body 16. After about 14 minutes, it was separated from the foam centrifuge into a concentrated foam 24 and a liquid 26 having a low TOC concentration, and started to flow out.
The concentration rate after centrifugation in the concentrated foam 24 was about 1.7 times, and the dilution rate after centrifugation of the diluted liquid 26 was about 0.6 times. From this result, it can be seen that the wastewater treatment method of the present invention can efficiently concentrate and purify suspended solids in soybean whey wastewater.

FIG. 1 is an apparatus diagram schematically showing a preferred embodiment of an apparatus used in the wastewater treatment method of the present invention. It is an expanded sectional view which shows typically the preferable embodiment of a microbubble generating means.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Microbubble generation means 2 Bubble tower 3 Liquid feed pump 4 Drainage distribution piping 5 Flowmeter 6 Pressure gauge 8 Valve 9 Compressor 11 Liquid layer (drainage layer)
12 Bubble aggregate (bubble aggregate layer)
13 Surface of drainage (interface between liquid layer and bubble aggregate layer)
15 Suction tube 16 Centrifuge body 17 Microbubbles 18 Drainage (soybean whey)
DESCRIPTION OF SYMBOLS 19 Top part of bubble column 23 Support | pillar 24 Concentrated foam layer 26 Diluted liquid layer 27 Axis rod 28 Substrate 32 Collection container 101 Nozzle main body 102 End wide nozzle 108 Base end part of end wide nozzle 109 End part of end wide nozzle 110 End part of end wide nozzle Space at the center of the divergent nozzle 113 Virtual axis 114 Air outlet 117 Frame 118 Fixing tool

Claims (5)

  Microbubbles are generated in the drainage, and a substance that can adhere to the surface of the bubbles in the drainage is attached to the surface of the microbubbles and captured. The aggregate of the microbubbles is taken out, centrifuged, and attached to the surface of the bubbles. A method for treating waste water from a food production process, wherein the material is concentrated and the waste water is purified.   The wastewater treatment method according to claim 1, wherein the substance that can adhere to the bubble surface is a protein.   The wastewater treatment method according to claim 1, wherein the substance that can adhere to the bubble surface is a carbohydrate.   The wastewater treatment method according to any one of claims 1 to 3, wherein the wastewater is soybean whey-containing water discharged during tofu production.   5. The centrifugal separation separates a phase in which a substance capable of adhering to the bubble surface is concentrated as a foam layer and a phase in which the substance capable of adhering to the bubble surface is diluted as a liquid layer. The wastewater treatment method according to any one of the above.

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