Method for treating starch-containing wastewater and treatment apparatus for starch-containing wastewater

Abstract

The present invention provides a method for treating starch-containing wastewater and a treatment apparatus for starch-containing wastewater that can recover starch for reuse while keeping processing costs down. [Solution] The method for treating starch-containing wastewater comprises: a first separation step of separating starch-containing wastewater into solid components and supernatant; a protease production step of adding microorganisms having protease-producing ability to the supernatant separated in the first separation step to cause the microorganisms to produce protease; a second separation step of separating the supernatant containing protease into solid components containing microorganisms; a purification step of mixing the supernatant separated in the second separation step and the solid components separated in the first separation step to purify the starch contained in the solid components; and a third separation step of separating the purified starch into supernatant. In the protease production step, the microorganism-containing solid components separated in the second separation step are returned and added as microorganisms.

Description

Technical Field

[0001] The present invention relates to a method for treating starch-containing wastewater and an apparatus for treating starch-containing wastewater.

Background Art

[0002] In sake brewing, food processing, etc., a large amount of rice washing wastewater is generated when polishing raw rice. Also, in noodle manufacturing such as udon and noodle restaurants, a large amount of cooked noodle wastewater is generated. These starch-containing wastewater such as rice washing wastewater and cooked noodle wastewater contain a large amount of starch that is hardly soluble, so if it is directly discharged into sewage, it will cause water pollution.

[0003] On the other hand, these starch-containing wastewater contain a large amount of useful starch. Therefore, it is desired to treat the starch-containing wastewater so that it can be discharged into sewage and recover and reuse the starch contained in the starch-containing wastewater.

[0004] Regarding the treatment of such starch-containing wastewater, in Patent Document 1, a treatment method is disclosed in which a protease-containing enzyme is added to rice washing wastewater to promote the self-aggregation of solid components in the wastewater, and the aggregated solid components are subjected to solid-liquid separation.

[0005] Also, in Patent Document 2, a treatment method is disclosed in which yeast having self-aggregation properties is added to cooked noodle wastewater, and the solid components aggregated with the yeast are subjected to solid-liquid separation.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] Patent Document 1 involves adding a protease-containing enzyme, and protease-containing enzymes are generally expensive. Therefore, processing costs become high.

[0008] Furthermore, in Patent Document 2, yeast is added before solid-liquid separation, so the separated and recovered solid components also contain yeast. Moreover, since the starch contained in the solid components is not purified, the surface of the starch is covered with protein. For this reason, it is difficult to reuse the starch contained in the separated and recovered solid components.

[0009] The present invention has been made in view of the above matters, and its objective is to provide a method for treating starch-containing wastewater and a treatment apparatus for starch-containing wastewater that can recover starch for reuse while keeping treatment costs down. [Means for solving the problem]

[0010] A method for treating starch-containing wastewater according to a first aspect of the present invention is: A first separation step in which starch-containing wastewater is separated into solid components and supernatant, A protease production step is to add a microorganism capable of producing protease to the supernatant separated in the first separation step and cause the microorganism to produce protease, A second separation step involves separating the supernatant containing protease from the solid component containing microorganisms, A purification step is performed by mixing the supernatant separated in the second separation step with the solid component separated in the first separation step, and purifying the starch contained in the solid component. The process includes a third separation step of separating the purified starch into a supernatant, In the protease production step, the microorganism-containing solid component separated in the second separation step is returned and added as the microorganism. It is characterized by the following:

[0011] Furthermore, it is preferable that the microorganism is a lactic acid bacterium, and that the protease is produced by lactic acid fermentation by the lactic acid bacterium.

[0012] Further, it is preferable that the microorganism does not produce glucoamylase.

[0013] Also, it is preferable that the microorganism belongs to the genus Lactobacillus.

[0014] The starch-containing wastewater treatment apparatus according to the second aspect of the present invention is a starch-containing wastewater storage tank for storing starch-containing wastewater, a first separation device for separating the starch-containing wastewater into solid components and supernatant, a solid component storage tank for storing the solid components separated by the first separation device, a protease production tank in which the supernatant separated by the first separation device and a microorganism having protease-producing ability are mixed to cause the microorganism to produce protease, a second separation device for separating into supernatant and microorganism-containing solid components, a purification tank in which the solid components separated by the first separation device and the supernatant separated by the second separation device are mixed to purify the starch contained in the solid components, and a microorganism return line for returning the microorganism-containing solid components separated by the second separation device to the protease production tank. It is characterized by this.

Advantages of the Invention

[0015] According to the present invention, it is possible to provide a method for treating starch-containing wastewater and a starch-containing wastewater treatment apparatus capable of recovering starch in a reusable manner while suppressing treatment costs.

Brief Description of the Drawings

[0016] [Figure 1] It is a diagram showing the steps of the method for treating starch-containing wastewater. [Figure 2] It is a diagram showing the configuration of the starch-containing wastewater treatment apparatus.

Embodiments for Carrying Out the Invention

[0017] <Method for treating starch-containing wastewater> The method for treating starch-containing wastewater comprises a first separation step, a protease production step, a second separation step, a purification step, and a third separation step, as shown in Fig. 1.

[0018] The starch-containing wastewater to be treated may be any wastewater containing starch, such as rice washing wastewater, cooked noodle wastewater, etc. Rice washing wastewater is produced in large quantities when polishing rice to pre-washed rice in sake brewing, food processing, etc. Also, cooked noodle wastewater is produced in large quantities when cooking noodles in noodle manufacturing such as udon, or in noodle restaurants. Since the solid components mainly composed of starch contained in rice washing wastewater and cooked noodle wastewater are hardly decomposable, if they are directly discharged into sewage, they may cause water pollution.

[0019] <First separation step> In the first separation step, the solid components contained in the starch-containing wastewater are separated from the supernatant. The separation method may be any method as long as it can separate the solid components from the supernatant, for example, centrifugation. The conditions for centrifugation are, for example, 4000 - 6000×G for 5 - 20 minutes.

[0020] <Protease production step> Microorganisms having protease-producing ability are added to the supernatant separated in the first separation step to produce protease. The microorganisms to be added are not limited as long as they can produce protease using the free sugar contained as a soluble component in the starch-containing wastewater in the supernatant separated in the first separation step as a substrate. The added microorganisms produce protease while growing. Protease is a hydrolase having a catalytic function that assists in the decomposition of proteins into smaller polypeptides and single amino acids.

[0021] Also, it is preferable that the microorganisms to be added do not produce glucoamylase. If glucoamylase is produced, in the purification step described later, starch saccharification may progress, and there is a risk that purified starch cannot be obtained.

[0022] Examples of microorganisms that possess such protease-producing ability include lactic acid bacteria. Examples of lactic acid bacteria include Lactobacillus species such as Lactobacillus rhamnosus (JCM1136 (accession no. D16552)) and Lactobacillus paracasei.

[0023] In the initial stages of this processing method, commercially available microorganisms capable of producing protease are added and used. After the microorganisms have grown sufficiently, the solid components containing the microorganisms separated in the second separation step described later are recycled and reused.

[0024] The duration and temperature of the protease production process can be set as appropriate, for example, 12 to 48 hours and 30 to 50°C.

[0025] <Second separation step> In the second separation step, the mixture obtained through the protease production step is subjected to solid-liquid separation to separate the solid components from the supernatant. Any known method that allows for separation can be used for solid-liquid separation, such as centrifugation. The centrifugation conditions are, for example, 4000-6000 × G for 5-20 minutes.

[0026] In the protease production process, if lactic acid bacteria are used as the microorganism capable of producing protease, the supernatant separated in the second separation step will be a protease mixture containing protease and lactic acid.

[0027] Furthermore, the solid component obtained in the second separation step is a microorganism-containing solid component containing microorganisms capable of producing protease. This microorganism-containing solid component is returned to the protease production step and added.

[0028] <Purification process> In the purification process, the solid components obtained in the first separation step and the protease mixture obtained in the second separation step are mixed and subjected to an enzymatic reaction with the protease.

[0029] The starch contained in the solid component obtained in the first separation step is covered with a protein layer on its surface. Proteases purify the starch by removing this surface protein through enzymatic action. Furthermore, the removal of the surface protein exposes the hydroxyl groups derived from the starch. The purified starch aggregates due to electrostatic interactions between these hydroxyl groups and the metal cations contained in the starch-containing wastewater.

[0030] The time and temperature of the purification process can be set as appropriate, for example, 2 to 12 hours and 30 to 50°C.

[0031] <Third separation step> The mixture, after undergoing the purification process, is subjected to solid-liquid separation to separate the solid component from the supernatant. Since the solid component is starch, purified starch can be obtained. The purified starch can be widely reused as a raw material for food, pharmaceuticals, cosmetics, etc., as saccharified starch or modified starch.

[0032] Furthermore, the supernatant obtained in the third separation step can also be reused. When lactic acid bacteria are used as the microorganism containing protease, the supernatant becomes a lactic acid fermentation liquid containing protease and lactic acid. By adding minerals such as sodium, potassium, and calcium to this lactic acid fermentation liquid, lactic acid can be converted into lactate. Then, by solid-liquid separation, the solid component, lactate, and the liquid component, the protease-containing solution, can be separated. The obtained lactate can be reused as a raw material for food additives, pharmaceuticals, etc.

[0033] In this embodiment, the solid component obtained in the second separation step, i.e., the microorganism-containing solid component containing microorganisms capable of producing protease, is returned to the protease production step and added. Except for the initial stage of processing, the microorganisms capable of producing protease are recycled and reused to produce protease, thus eliminating the need for expensive protease for each processing step and reducing processing costs.

[0034] <Treatment for starch-containing wastewater> The above-described method for treating starch-containing wastewater can be carried out using, for example, the following starch-containing wastewater treatment apparatus. As shown in Figure 2, the starch-containing wastewater treatment apparatus 1 comprises a starch-containing wastewater storage tank 10, a first separation apparatus 20, a solid component storage tank 30, a protease production tank 40, a second separation apparatus 50, a protease mixed liquid storage tank 60, a microbial storage tank 70, a microbial return line 71, a purification tank 80, and a third separation apparatus 90.

[0035] The starch-containing wastewater storage tank 10 is a tank for storing starch-containing wastewater. The starch-containing wastewater stored in the starch-containing wastewater storage tank 10 is sent to the first separation device 20 by a pump (not shown) or the like.

[0036] The first separation device 20 separates the starch-containing wastewater into solid components and supernatant. The first separation device 20 can be any device capable of solid-liquid separation, such as a centrifuge. The solid components separated here are sent to the solid component storage tank 30. The separated supernatant is sent to the protease production tank 40.

[0037] Microorganisms capable of producing protease flow into the protease production tank 40 via the microbial return line 71. The supernatant separated in the first separation device 20 and the microbial-containing solid components stored in the microbial storage tank 70 described later are then used to produce protease. In the protease production tank 40, protease is produced by the microorganisms capable of producing protease.

[0038] The mixture processed in the protease production tank 40 is sent to the second separation device 50, which separates the mixture into solid and liquid components, separating it into a supernatant containing microorganisms and protease, i.e., a protease mixture. The separated microorganism-containing solid components are sent to the microorganism storage tank 70, and the protease mixture is sent to the protease mixture storage tank 60. The second separation device 50 can be any device capable of solid-liquid separation, such as a centrifuge.

[0039] The microbial storage tank 70 stores the microbial-containing solid components. As described above, the components are returned from the microbial storage tank 70 to the protease production tank 40 via the microbial return line 71.

[0040] The purification tank 80 receives solid components from the solid component storage tank 30 and a protease mixture from the protease mixture storage tank 60. In the purification tank 80, the solid components are purified by the protease.

[0041] In the third separation device 90, the mixture treated in the purification tank 80 is subjected to solid-liquid separation to separate it into purified starch and supernatant. The third separation device 90 can be any device capable of solid-liquid separation, such as a centrifuge.

[0042] Furthermore, if the microorganism used in the treatment device 1 for starch-containing wastewater is lactic acid bacteria, the device may also include a mineral storage tank 100, a sedimentation tank 110, and a fourth separation device 120.

[0043] Mineral storage tank 100 stores an aqueous solution containing mineral ions such as sodium ions, potassium ions, and calcium ions. Sedimentation tank 110 receives the supernatant separated by the third separation device 90 and the mineral ion-containing aqueous solution from mineral storage tank 100. The supernatant sent to sedimentation tank 110 is a lactic acid fermentation liquid, which reacts with the added minerals to produce lactate.

[0044] In the fourth separation apparatus 120, the mixed liquid that has passed through the sedimentation tank 110 flows in and is separated into lactate and supernatant. The fourth separation apparatus 120 can be any apparatus capable of solid-liquid separation, such as a centrifuge. [Explanation of Symbols]

[0045] 1. Treatment device for starch-containing wastewater 10. Starch-containing wastewater storage tank 20 First Separation Device 30 Solid component storage tank 40 Protease production cells 50 Second separation device 60 Protease mixture storage tank 70 Microbial storage tank 71 Microbial Return Line 80 Purification tank 90 Third Separation Device 100 Mineral storage tanks 110 Sedimentation tank 120 Fourth Separation Device

Claims

1. A first separation step in which starch-containing wastewater is separated into solid components and supernatant, A protease production step is to add a microorganism capable of producing protease to the supernatant separated in the first separation step and cause the microorganism to produce protease, A second separation step involves separating the supernatant containing protease from the solid component containing microorganisms, A purification step is performed by mixing the supernatant separated in the second separation step with the solid component separated in the first separation step, and purifying the starch contained in the solid component. The process includes a third separation step of separating the purified starch into a supernatant, In the protease production step, the microorganism-containing solid component separated in the second separation step is returned and added as the microorganism. A method for treating starch-containing wastewater, characterized by the above.

2. The microorganism is a lactic acid bacterium, and the lactic acid fermentation by the lactic acid bacterium produces the protease. The method for treating starch-containing wastewater according to feature 1.

3. The aforementioned microorganisms do not produce saccharifying enzymes. The method for treating starch-containing wastewater according to feature 1.

4. The aforementioned microorganism belongs to the genus Lactobacillus. The method for treating starch-containing wastewater according to feature 1.

5. A starch-containing wastewater storage tank for storing starch-containing wastewater, A first separation device for separating the starch-containing wastewater into solid components and supernatant, A solid component storage tank for storing the solid component separated by the first separation device, A protease production tank is provided in which the supernatant separated by the first separation device is mixed with a microorganism capable of producing protease, and the microorganism is made to produce protease. A second separation device separates the supernatant from the solid component containing microorganisms, A purification tank in which the solid components separated by the first separation device and the supernatant separated by the second separation device are mixed to purify the starch contained in the solid components, The system includes a microbial return line that returns the microbial-containing solid component separated by the second separation device to the protease production tank, A treatment apparatus for starch-containing wastewater, characterized by the above.

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