JP6837750B2 - Oil-containing wastewater treatment system and oil-containing wastewater treatment method - Google Patents

Description

The present invention relates to a fat-containing wastewater treatment system and a fat-containing wastewater treatment method.

As a method for treating wastewater containing fats and oils such as wastewater from food factories, as shown in Patent Document 1, a method of separating and removing fats and oils and then treating the separated water by aerobic treatment is common.

Japanese Unexamined Patent Publication No. 4-235799

However, in the method for treating oil and fat-containing wastewater described in Patent Document 1, a separate treatment for the separated and removed oil and fat is required. A method of biological treatment in an aerobic state without removing the fat and oil from the wastewater containing fat and oil is also being studied, but it is said that the power required for aeration will be considerably large and the cost will increase in order to achieve the aerobic state. There are challenges.

The present invention has been made in view of the above, and an object of the present invention is to provide a fat-containing wastewater treatment system and a fat-containing wastewater treatment method capable of treating fat-containing wastewater at a lower cost.

In order to achieve the above object, the oil-and-fat-containing wastewater treatment system according to one embodiment of the present invention includes a pre-stage treatment unit that anaerobically treats the oil-and-fat-containing wastewater in a limited oxygen supply state, and a pre-stage treatment unit after the pre-stage treatment. It is characterized by comprising an anaerobic treatment unit for anaerobically treating the oil-containing wastewater.

Further, the oil / fat-containing wastewater treatment method according to one embodiment of the present invention includes a pre-stage treatment step of anaerobically treating the oil-containing wastewater in a limited oxygen supply state and an anaerobic treatment of the oil-fat-containing wastewater after the pre-stage treatment step. It is characterized by having a processing step.

According to the above-mentioned oil-containing wastewater treatment system and oil-containing wastewater treatment method, anaerobic treatment is performed on the oil-containing wastewater under a limited oxygen supply state before the anaerobic treatment, and at this time, limited oxygen is applied. Decomposition of fats and oils is promoted by facultative anaerobes that predominate in the anaerobic treatment state in the supply state. Therefore, while adopting an anaerobic treatment that can be treated at a lower cost than the aerobic treatment, the fats and oils are suitably decomposed and the wastewater containing the fats and oils can be treated.

Here, the pre-stage processing unit and the anaerobic processing unit can be in an independent manner.

As described above, since the pre-stage treatment unit and the anaerobic treatment unit are independent, the anaerobic treatment in the limited oxygen supply state in the pre-stage treatment unit and the anaerobic treatment in the anaerobic treatment unit can be performed. It becomes possible to process under more preferable conditions, which leads to improvement in processing efficiency.

The redox potential of the pre-stage treatment unit can be in an embodiment of −200 mV to −300 mV.

As described above, when the redox potential of the pre-stage treatment section is set to -200 mV to -300 mV, the facultative anaerobic bacteria, which are the main constituents of the pre-stage treatment section that perform anaerobic treatment under a limited oxygen supply state, are in a predominant state. It can be preferably maintained.

An embodiment may be provided in which a return unit for returning a part of sludge and treated water from the anaerobic treatment unit to the pre-treatment unit is provided.

By providing the return unit as described above, it is possible to return facultative anaerobes having a high ability to decompose fats and oils together with a part of sludge and treated water, and maintain the facultative anaerobes in the pretreatment unit. Therefore, the oil / fat decomposition performance in the pre-stage treatment section is improved.

According to the present invention, there is provided a fat-containing wastewater treatment system and a fat-containing wastewater treatment method capable of treating fat-containing wastewater at a lower cost.

It is a figure explaining the wastewater treatment system which concerns on 1st Embodiment. It is a figure explaining the wastewater treatment system which concerns on 2nd Embodiment. It is a figure explaining the wastewater treatment system which concerns on 3rd Embodiment. It is a figure explaining the wastewater treatment system which concerns on a comparative example. It is a figure which shows the analysis result of the bacterial flora of the pre-stage treatment tank in the system which concerns on Example. It is a figure which shows the analysis result of the bacterial flora of the acid production tank in the system which concerns on Example. It is a figure which shows the analysis result of the bacterial flora of the acid production tank in the system which concerns on a comparative example.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicate description will be omitted.

(First Embodiment)
FIG. 1 is a schematic configuration diagram showing an oil-and-fat-containing wastewater treatment system that employs the oil-and-fat-containing wastewater treatment method according to the first embodiment.

As shown in FIG. 1, the wastewater treatment system 100 (fat-containing wastewater treatment system) is a facility for treating organic wastewater containing fats and oils (fat-containing wastewater), and introduces fat-containing wastewater as raw water for pretreatment. A pre-stage treatment tank 1 (pre-stage treatment unit) that performs anaerobic treatment in a limited oxygen supply state, an acid generation tank 2 that acid-ferments the water after the pre-stage treatment, and methane fermentation in which an acid fermentation liquid is introduced and methane fermentation is performed. It has a tank 3 and. The acid generation tank 2 and the methane fermentation tank 3 function as an anaerobic treatment unit that performs biological treatment (anaerobic treatment) in an anaerobic state.

The pre-stage treatment tank 1 receives the oil-and-fat-containing wastewater via the line L1. The pretreatment tank 1 includes an oxygen supply unit 10 for maintaining the water in the tank in a limited oxygen supply state.

In the present embodiment, the limited oxygen supply state refers to a state in which the dissolved oxygen amount (DO) is close to 0 mg / L under the supply of oxygen-containing gas. Therefore, a state where the dissolved oxygen amount (DO) is 0 mg / L and the oxidation-reduction potential (ORP) is 0 mV or less, for example, when DO is 0 mg / L and ORP is -100 mV, the oxygen-containing gas is generally anaerobic. When supplying, it corresponds to the limited oxygen supply state in this embodiment.

Air or the like can be used as the oxygen-containing gas supplied to the pretreatment tank 1. Further, the highly concentrated oxygen obtained by using a gas separation membrane, a PSA (pressure fluctuation adsorption) type gas separation device, or the like may be supplied to the pretreatment tank 1. Further, as the oxygen supply unit 10, known gas supply means such as an air diffuser pipe, an air diffuser panel, a pipe having an opening, a micro bubble generator, a blower fan, and an underwater aerator can be used.

In the pretreatment tank 1, the water in the tank is maintained in a limited oxygen supply state by introducing the oxygen-containing gas by the oxygen supply unit 10, and the oil-fat-containing wastewater is anaerobically treated in a limited oxygen supply state (Oxygen-). Limited anaerobic treatment). A general carrier such as urethane, PVA, or polyolefin can be arranged in the pretreatment tank 1 for retaining microorganisms. The carrier may be in any shape such as a cube, a rectangular parallelepiped, a columnar shape, a cylindrical shape, and a string shape as long as the microorganism can be fixed.

In the pre-stage treatment tank 1, it is preferable that the ORP is maintained in a state of −100 mV to −500 mV by the oxygen supply unit 10. In this state, the anaerobic treatment in the pretreatment tank 1 under the limited oxygen supply state is preferably performed, the hydrolysis of fats and oils and β-oxidation are promoted, and lower fatty acids are produced. The anaerobic treatment in the limited oxygen supply state in the pre-stage treatment tank 1 will be described later.

The acid-producing tank 2 introduces the fat-containing wastewater biologically treated in the pretreatment tank 1 via the line L2, and the organic substances contained in the fat-containing wastewater by the acid-producing bacteria contained in the tank ( Decomposes sugars, proteins, high molecular weight organic acids, alcohols, etc.) to produce lower fatty acids.

The methane fermentation tank 3 introduces water from the acid generation tank 2 via the line L3, decomposes lower fatty acids by anaerobic treatment by methanogens housed in the tank, and contains methane and carbon dioxide as main components. Generates biogas. The treated water after the anaerobic treatment is transferred to the subsequent stage by the line L4. Biogas is recovered and used as energy.

Further, the methane fermentation tank 3 is connected to a line L5 that returns a part of sludge and treated water from the methane fermentation tank 3 to the acid generation tank 2 in order to increase the cell concentration of the acid production tank 2. Similarly, in order to increase the cell concentration of the pre-stage treatment tank 1, a line L6 for returning a part of sludge and treated water from the methane fermentation tank 3 to the pre-stage treatment tank 1 is connected. The line L6 functions as a return unit for returning a part of sludge and treated water from the anaerobic treatment unit to the pre-treatment unit.

Subsequently, the water treatment method performed by the wastewater treatment system 100 according to the present embodiment will be described. First, the oil-and-fat-containing wastewater is supplied to the pre-treatment tank 1 via the line L1, and the oxygen-containing gas is introduced into the tank by the oxygen supply unit 10, so that the water in the pre-treatment tank 1 is supplied with limited oxygen. Anaerobic treatment is performed while maintaining the state (pre-stage treatment step). By maintaining a limited oxygen supply state, the facultative anaerobic bacteria in the tank can be in a predominant state, and the decomposition of fats and oils contained in the fats and oils-containing wastewater into lower fatty acids is promoted. ..

Subsequently, the water subjected to the pre-stage treatment in the pre-stage treatment tank 1 is supplied to the acid generation tank 2 via the line L2 and biologically treated under an anaerobic state. When oxygen is sufficiently consumed in the pretreatment tank 1, the acid-producing tank 2 and subsequent tanks are in an anaerobic state, and the acid-producing bacteria contained in the tank decompose the organic substances contained in the oil-containing wastewater into lower fatty acids. Will be done.

Further, the water biologically treated in the acid generation tank 2 is supplied to the methane fermentation tank 3 via the line L3, and the biological treatment is performed under an anaerobic state. As a result, lower fatty acids in water are decomposed into carbon dioxide and methane (anaerobic treatment step). The methane obtained by these steps can be effectively used as an energy source, for example. Further, a part of the sludge and the treated water from the methane fermentation tank 3 is returned to the pre-stage treatment tank 1 and the acid generation tank 2.

Here, in the wastewater treatment method in the wastewater treatment system 100 according to the present embodiment, anaerobic treatment is performed in the pre-stage treatment tank 1 in a limited oxygen supply state. In the pretreatment tank 1, by forming the limited oxygen supply state as described above, the facultative anaerobic bacteria in the tank can be in a predominant state. By making the facultative anaerobic bacteria predominant, the decomposition of fats and oils into lower fatty acids in the wastewater containing fats and oils is promoted.

Fats and oils are decomposed into lower fatty acids through hydrolysis and β-oxidation. Fats and oils (glycerin esters) are first decomposed into glycerin and higher fatty acids by hydrolysis. After that, the higher fatty acid is decomposed into a lower fatty acid by β-oxidation. When a facultative anaerobic bacterium is predominantly formed in the flora in the pretreatment tank 1, hydrolysis and β for decomposing fats and oils into lower fatty acids are compared with the anaerobic bacterium predominant state. Oxidation is promoted.

As a method for treating wastewater containing fats and oils, a method has conventionally been used in which the separated water is treated by aerobic treatment after separating and removing the fats and oils. However, since the cost for separating and removing fats and oils and the cost for disposing of the separated and removed fats and oils increase, a method for directly biologically treating the wastewater containing fats and oils has begun to be studied. When biologically treating wastewater containing fats and oils, it is necessary to decompose fats and oils, which are higher fatty acids, so it is conceivable that aerobic treatment with higher decomposition ability is used. However, when aerial treatment of wastewater containing fats and oils is performed, a large-capacity aeration tank is required, and energy such as aeration power is required, which increases the cost. On the other hand, it is possible to reduce the power cost related to wastewater treatment by anaerobically treating the wastewater containing fats and oils, but since the decomposition rate of fats and oils is slower than that of aerobic treatment, there is a problem in terms of efficiency. was there.

On the other hand, in the wastewater treatment method in the wastewater treatment system 100 according to the present embodiment, the flora is controlled by setting the pre-stage treatment tank 1 as a limited oxygen supply state, and facultative anaerobic bacteria form a predominant situation. By performing biological treatment, hydrolysis of fats and oils and β-oxidation are promoted. After that, by performing anaerobic treatment in the acid generation tank 2 and the methane fermentation tank 3, even if it is a biological treatment such as anaerobic treatment that takes a long time to decompose fats and oils, such as wastewater containing fats and oils, the pretreatment is performed. Since the decomposition of fats and oils is promoted by the anaerobic treatment in the limited oxygen supply state in the tank 1, it is possible to suppress the decrease in the treatment speed even if the subsequent stage is the anaerobic treatment under the anaerobic state. Therefore, it is possible to treat the wastewater containing oil and fat at a lower cost.

Further, since the pre-stage treatment tank 1 and the acid generation tank 2 and the methane fermentation tank 3 are independent as in the wastewater treatment system 100, the anaerobic treatment in the pre-stage treatment tank 1 in a limited oxygen supply state is performed. , And each of the anaerobic treatments in the acid generation tank 2 and the methane fermentation tank 3 can be treated under more preferable conditions, which leads to an improvement in treatment efficiency.

Further, by setting the pre-stage treatment tank 1 in a limited oxygen supply state, when facultative anaerobic bacteria become predominant in the bacterial flora in the pre-stage treatment tank 1, the facultative anaerobic bacteria that survive in the pre-stage treatment tank 1 survive. The bacteria flow into the acid production tank 2 and the methane fermentation tank 3 in the subsequent stage as the water moves. Facultative anaerobic bacteria are bacteria that can be grown even in an anaerobic state, such as an acid production tank 2 and a methane fermentation tank 3. The facultative anaerobic bacteria that have flowed into the acid generation tank 2 and the methane fermentation tank 3 decompose the fats and oils into lower fatty acids in each tank in the same manner as the facultative anaerobic bacteria in the pretreatment tank 1. Therefore, the decomposition of fats and oils in the fats and oils-containing wastewater can be further promoted.

Further, by returning the facultative anaerobic bacteria having a high ability to decompose fats and oils together with a part of sludge and treated water from the methane fermentation tank 3 to the acid generation tank 2, the facultative anaerobic bacteria in the acid generation tank 2 are returned by the line L5. The maintenance of sexual bacteria can be preferably performed. Similarly, by returning the facultative anaerobic bacteria having a high ability to decompose fats and oils together with a part of sludge and treated water from the methane fermentation tank 3 to the pre-treatment tank 1, the facultative anaerobic bacteria in the pre-treatment tank 1 are returned by the line L6. The maintenance of anaerobic bacteria can be preferably performed.

In the pretreatment tank 1, the ORP is maintained at −100 mV to −500 mV, so that facultative anaerobic bacteria can form a predominant state. Of these, when the ORP is in a state of −200 mV to −300 mV, a state in which facultative anaerobic bacteria predominate can be suitably maintained. When the ORP is lower than −500 mV, the proportion of facultative anaerobic bacteria decreases and the proportion of anaerobic bacteria increases, so that the treatment efficiency of fats and oils may decrease. On the other hand, when the ORP becomes larger than -100 mV, the proportion of facultative anaerobes decreases and the proportion of aerobic bacteria increases, so that easily decomposable organic substances other than fats and oils are decomposed. In this case, the amount of organic matter to be anaerobically treated in the subsequent stage is reduced, and as a result, the amount of biogas generated is reduced. As described above, since biogas is recovered and used as energy, a decrease in organic matter subject to anaerobic treatment leads to energy loss.

Further, when the residence time of the oil-containing wastewater in the pre-stage treatment tank 1 becomes long and the amount of organic substances decomposed by the anaerobic treatment in the limited oxygen supply state in the pre-stage treatment tank 1 increases, the target of the anaerobic treatment is the same as described above. Organic matter is reduced, leading to energy loss. Therefore, in the pre-treatment tank 1, the decomposition rate of organic matter is about 10% to 50% of the total amount of organic matter in the oil-containing wastewater before charging, so that the environment in the pre-treatment tank 1 and the oil-containing wastewater It is preferable to set the residence time. The residence time of the oil-and-fat-containing wastewater in the pre-stage treatment tank 1 varies greatly depending on the content of the organic matter containing the oil and fat in the oil-and-fat-containing wastewater, but can be, for example, about 1 hour to 12 hours.

In the above embodiment, an example in which the oxygen supply unit 10 is provided to maintain the pre-stage treatment tank 1 in a limited oxygen supply state has been described, but by maintaining the oxygen supply state in a limited state, The purpose is to control the state of the flora so that facultative anaerobes dominate. Therefore, the method for maintaining a limited oxygen supply state is not limited to the supply of oxygen-containing gas, and for example, a limited oxygen supply state is provided by adding an oxidizing agent / reducing agent, a pH adjuster, a nutrient salt, or the like. It may be configured to maintain. By adjusting the pH to about 6 to 8, facultative anaerobic bacteria tend to predominate in the state of the flora.

Further, in the above embodiment, the facultative anaerobic bacteria having a high ability to decompose fats and oils together with a part of sludge and treated water are returned from the methane fermentation tank 3 to the acid generation tank 2 and the pretreatment tank 1 by the lines L5 and L6. Although the configuration has been described, the line for returning a part of sludge and treated water from the methane fermenter 3 may be only one side of the lines L5 and L6.

(Second Embodiment)
Next, the wastewater treatment system 200 according to the second embodiment of the present invention will be described with reference to FIG. The difference between the wastewater treatment system 200 according to the present embodiment and the wastewater treatment system 100 according to the first embodiment is that the sludge and a part of the treated water are returned from the methane fermentation tank 3 to the pretreatment tank 1 instead of the line L6. Therefore, a line L7 for returning a part of sludge and treated water from the acid generation tank 2 to the pre-stage treatment tank 1 is provided.

When a facultative anaerobic bacterium having a high ability to decompose fats and oils is returned from the acid generation tank 2 to the pretreatment tank 1 by the line L7 as in the above wastewater treatment system 200. Even so, the facultative anaerobic bacteria can be preferably maintained in the pretreatment tank 1.

It should be noted that the facultative anaerobic bacteria in the pretreatment tank 1 are provided even if the line L5 for returning the sludge and a part of the treated water from the methane fermentation tank 3 to the acid generation tank 2 is not provided and only the line L7 is provided. Can be preferably maintained.

(Third Embodiment)
Next, the wastewater treatment system 300 according to the third embodiment of the present invention will be described with reference to FIG. The wastewater treatment system 300 according to the present embodiment is different from the wastewater treatment system 100 according to the first embodiment in that the pre-stage treatment tank 1 also serves as the acid generation tank 2.

That is, the wastewater treatment system 300 has a pre-stage treatment tank / acid generation tank 4 in front of the methane fermentation tank 3, and maintains the pre-stage treatment tank / acid generation tank 4 in a limited oxygen supply state. , Promotes the decomposition of fats and oils contained in fats and oils-containing wastewater by anaerobic bacteria, and organic substances (sugars, proteins, high polymers) contained in fats and oils-containing wastewater by acid-producing bacteria contained in the tank. Decomposes acids, alcohols, etc.) to produce lower fatty acids. Water that has undergone biological treatment in the pretreatment tank / acid generation tank 4 is supplied to the methane fermentation tank 3 via the line L3, and the biological treatment is performed under an anaerobic state.

Further, in the wastewater treatment system 300, sludge and a part of the treated water are returned from the methane fermentation tank 3 to the pretreatment tank / acid generation tank 4 by the line L8.

Also in the above wastewater treatment system 300, the bacterial flora is controlled by setting the pre-stage treatment tank / acid generation tank 4 as a limited oxygen supply state, and facultative anaerobic bacteria form a predominant situation to perform biological treatment. As a result, not only the decomposition of organic matter by acid-producing bacteria but also the hydrolysis of fats and oils and β-oxidation can be promoted. After that, by performing anaerobic treatment in the methane fermentation tank 3, even if it is a biological treatment such as anaerobic treatment that takes time to decompose fats and oils, such as wastewater containing fats and oils, the pretreatment tank / acid generation tank 4 Since the decomposition of fats and oils is promoted by the anaerobic treatment in the limited oxygen supply state in the above, the decrease in the treatment speed can be suppressed even if the anaerobic treatment is performed in the anaerobic state in the latter stage. Therefore, it is possible to treat the wastewater containing oil and fat at a lower cost.

Further, the line L8 is configured to return facultative anaerobic bacteria having a high ability to decompose fats and oils together with a part of sludge and treated water from the methane fermentation tank 3 to the pre-treatment tank / acid generation tank 4 for pre-treatment. The facultative anaerobic bacteria can be preferably maintained in the tank / acid generation tank 4.

As described above, the present invention is not limited to the above embodiment, and various modifications are possible. For example, the type of each tank is not particularly limited, and various forms can be taken.

Further, the dissolved oxygen concentration detector (DO meter) and the redox potential detector (ORP meter) are attached to the pre-stage treatment tank 1 and the acid generation tank 2 (or the pre-stage treatment tank / acid generation tank 4) to provide oxygen. The amount of oxygen supplied from the supply unit 10 and / or the line between the pre-treatment tank 1, the acid generation tank 2 and the methane fermentation tank 3 (or between the pre-treatment tank / acid generation tank 4 and the methane fermentation tank 3) is used. The amount of sludge and treated water returned may be controlled.

In addition, an organic matter concentration detector (for example, a COD meter) for the treated water from the methane fermenter 3 may be attached to control the amount of sludge and treated water returned.

Further, the methane fermentation unit may be in any form such as EGSB (Expanded Granular Sludge Bed), UASB (Upflow Anaerobic Sludge Blanket), and anaerobic treatment using a carrier or membrane separation. Further, the anaerobic treatment may be performed only in the methane fermentation tank 3 without the acid generation tank 2.

Further, in the above embodiment, the configuration in which the anaerobic treatment under the limited oxygen supply state is performed in the pre-stage treatment tank 1 and the anaerobic treatment under the normal anaerobic state is performed in the methane fermentation tank 3 has been described. Instead of preparing a tank for anaerobic treatment in the supply state and anaerobic treatment in the anaerobic state, for example, at least the anaerobic treatment in the limited oxygen supply state in the pipe and the anaerobic treatment in the anaerobic state. One of them may be performed. Further, the pre-stage processing unit that performs anaerobic treatment in a limited oxygen supply state and the anaerobic treatment unit that performs anaerobic treatment under an anaerobic state can be the same. In this case, for example, by creating a state close to an anaerobic state such as a state in which the dissolved oxygen amount (DO) is 0 mg / L and the redox potential (ORP) is 0 mV or less under the supply of an oxygen-containing gas, it is limited. It is possible to simultaneously perform the anaerobic treatment in the oxygen supply state and the anaerobic treatment in the anaerobic state.

Hereinafter, the present invention will be described in more detail based on Examples and Comparative Examples, but the present invention is not limited to the following Examples.

(Wastewater treatment system according to the example)
As an example, the wastewater treatment system 100 shown in FIG. 1 was prepared.

(Wastewater treatment system according to a comparative example)
As a comparative example, as shown in FIG. 4, a wastewater treatment system 400 that does not perform anaerobic treatment under the limited oxygen supply state in the previous stage was prepared. The wastewater treatment system 400 shown in FIG. 4 is a system that does not include the pre-stage treatment tank 1 and directly flows into the acid generation tank 2 by the line L1 using the oil-containing wastewater as raw water. Further, although the line L5 for returning the sludge from the methane fermentation tank 3 and a part of the treated water to the acid generation tank 2 is provided, it is not provided with the line L6 for returning the sludge and the treated water to the pre-stage treatment tank 1.

<Evaluation of the amount of fat decomposition during wastewater treatment containing fats and oils>
A 100-fold diluted solution of milk was used as the liquid to be treated (the liquid corresponding to the wastewater containing fats and oils). At this time, the COD concentration of the liquid to be treated was 2,000 to 2,300 mg / L, and the concentration of the N-hexane extract, which is an index of the oil and fat concentration in the liquid to be treated, was 200 to 260 mg / L.

In the wastewater treatment system 100 according to the embodiment, the amount of air blown by the oxygen supply unit 10 was adjusted so that the ORP was about −350 to −250 mV in the pre-stage treatment tank 1. The DO of the pre-stage treatment tank 1 at this time was almost 0. Further, in the pretreatment tank 1, the pH was adjusted to 7 with caustic soda. Further, the treated water of the methane fermentation tank 3 was returned to the pretreatment tank 1 as a seeding solution of about 10% with respect to the raw water via the line L6.

Further, in both the wastewater treatment system 100 according to the example and the wastewater treatment system 400 according to the comparative example, the pH of the acid generation tank 2 was adjusted to 7 with caustic soda. Further, the treated water of the methane fermentation tank 3 was returned to the acid generation tank 2 as a seeding solution of about 40% of the raw water.

Further, in both the wastewater treatment system 100 according to the example and the wastewater treatment system 400 according to the comparative example, the methane fermentation tank 3 was filled with granules so as to have an effective capacity of 1.5 L.

Table 1 shows the results of operating both the wastewater treatment system 100 according to the example and the wastewater treatment system 400 according to the comparative example under the above conditions. The first and second embodiments are the results of changing the operating conditions in the wastewater treatment system 100. As shown in Table 1, the first embodiment is an operating condition in which the air supply amount is suppressed and the ORP is set low. Further, the second embodiment is an operating condition in which the air supply amount is adjusted and the ORP is set to be about 50 higher than that of the first embodiment.

Further, Comparative Example 1 is the result of operating the wastewater treatment system 400. Under each condition in Examples 1 and 2 and Comparative Example 1, the operation was carried out for 2 weeks or more after the acclimatization operation period of about 1 month, and when the treatment state became stable, the oil and fat concentration in each tank was measured.

According to the results in Table 1, the oil and fat concentrations of the pre-stage treatment tank, the acid generation tank and the treated water were lower in Example 2 than in Example 1. In Example 2, the air supply amount was adjusted, the ORP was set to be about 50 higher than that in Example 1, and the operation was performed in a state where the average ORP was about −250 mV. As a result, in Example 2, it is considered that the decomposition of fats and oils has progressed.

Further, Comparative Example 1 is the result of a test conducted in a conventional system in which the anaerobic treatment is not performed in the limited oxygen supply state in the pre-stage treatment tank 1. Since the decomposition rate of fats and oils is slow in the acid generation tank 2 of the conventional wastewater treatment system 400, the capacity of the acid generation tank 2 is larger than the combined capacity of the pre-stage treatment tank 1 and the acid generation tank 2 in Examples 1 and 2. The test was conducted under large conditions. However, the fat and oil concentration of the treated water was as high as 59 mg / L, and it was confirmed that the decomposition of the fat and oil did not proceed more than other conditions.

Table 2 shows the amount of fats and oils decomposed in each tank obtained from the results of Examples 1 and 2 and Comparative Example 1 above. Table 3 shows the oil and fat decomposition rates in each tank. The amount of fats and oils decomposed was calculated in consideration of the return of sludge and treated water from the methane fermenter 3. The oil / fat decomposition rate is the result of dividing the oil / fat decomposition amount in Table 2 by the water tank capacity of each tank.

According to the results in Table 3, comparing Examples 1 and 2 with Comparative Example 1, it was confirmed that the oil / fat decomposition rate was higher when the pre-stage treatment tank 1 was provided (Examples 1 and 2). .. Further, the oil / fat decomposition rate was higher in Example 2 than in Example 1. This is considered to be due to the difference in ORP.

<Analysis of flora in each tank>
The bacterial flora in the pre-stage treatment tank 1 and the acid production tank 2 when operated under the conditions of the above-mentioned Example 2 in the wastewater treatment system 100 according to the example was analyzed. The results are shown in FIG. 5 (pre-treatment tank) and FIG. 6 (acid generation tank). In addition, the flora in the acid generation tank 2 in the wastewater treatment system 400 according to the comparative example was analyzed. The result is shown in FIG. In FIGS. 5 to 7, the analysis results are shown as a pie chart. Each number in FIGS. 5 to 7 shows the ratio of each bacterial species in the flora as a percentage (%).

As shown in FIGS. 5 and 6, in the wastewater treatment system 100 according to the embodiment, facultative anaerobes such as Brachymonas, Cloacibacterium, Lactococcus, and Acetobacter are prioritized in both the pretreatment tank 1 and the acid generation tank 2. It was. On the other hand, in the acid generation tank 2 of the conventional wastewater treatment system 400 according to the comparative example, obligate anaerobic bacteria such as Clostridium and Blautia were prioritized. As described above, in the wastewater treatment system 100 according to the embodiment, it is considered that facultative anaerobic bacteria become dominant and the decomposability of fats and oils is enhanced by performing anaerobic treatment in the pre-stage treatment tank 1 in a limited oxygen supply state. Be done.

The flora of the granules in the methane fermentation tank 3 in the wastewater treatment system 100 was also confirmed. In addition to methane bacteria such as Methanosaeta and Methanosaeta, obligate anaerobic bacteria such as Thermobaculaceae, Syntrophaceae, Syntrophus and Treponema Was detected. It is considered that the flora existing in the liquid other than the granule of the methane fermentation tank is almost the same as the flora of the acid production tank in the previous stage. Therefore, it is considered that the environment is such that the decomposition of fats and oils easily proceeds even in the methane fermentation tank 3 in the wastewater treatment system 100.

1 ... Pre-stage treatment tank, 2 ... Acid generation tank, 3 ... Methane fermentation tank, 4 ... Pre-stage treatment tank / acid generation tank, 100, 200, 300 ... Wastewater treatment system.

Claims (5)

A pre-stage treatment unit that anaerobicly treats oil-containing wastewater under a limited oxygen supply condition,
An anaerobic treatment unit that anaerobically treats the oil-containing wastewater after the pre-stage treatment in the pre-stage treatment unit is provided.
The first-stage treatment unit is a fat-containing wastewater treatment system that controls the dissolved oxygen amount to be 0 mG / L and the redox potential to be 0 mV or less under the supply of oxygen-containing gas. A pre-stage treatment unit that anaerobicly treats oil-containing wastewater under a limited oxygen supply condition,
An anaerobic treatment unit that anaerobically treats the oil-containing wastewater after the pre-stage treatment in the pre-stage treatment unit.
A return unit for returning a part of sludge and treated water from the anaerobic treatment unit to the pre-treatment unit is provided.
The first-stage treatment unit is a fat-containing wastewater treatment system in which the amount of dissolved oxygen is 0 mG / L and the redox potential is 0 mV or less under the supply of oxygen-containing gas. The pre-stage processing unit and the anaerobic processing unit are independent or
The oil-and-fat-containing wastewater treatment system according to claim 1 or 2, wherein the anaerobic treatment unit includes an acid generation tank and a methane fermentation tank provided after the acid generation tank. A pre-treatment process that anaerobically treats oil-containing wastewater under a limited oxygen supply condition,
It has an anaerobic treatment step of anaerobically treating the oil-containing wastewater after the pretreatment step.
The pretreatment step is a fat-containing wastewater treatment method performed in a state where the amount of dissolved oxygen is 0 mG / L and the redox potential is controlled to be 0 mV or less under the supply of oxygen-containing gas. A pre-treatment process that anaerobically treats oil-containing wastewater under a limited oxygen supply condition,
An anaerobic treatment step of anaerobically treating the oil-containing wastewater after the pre-treatment in the pre-treatment step,
It has a return step of returning a part of sludge and treated water from the anaerobic treatment step to the pre-treatment step.
The first-stage treatment step is a fat-containing wastewater treatment method performed in a state where the amount of dissolved oxygen is 0 mG / L and the redox potential is 0 mV or less under the supply of oxygen-containing gas.