JP6203560B2 - Organic wastewater treatment method and organic wastewater treatment apparatus - Google Patents

Description

  The present invention relates to an organic wastewater treatment method and an organic wastewater treatment apparatus for removing nitrogen and phosphorus from organic wastewater such as rice bran processing wastewater.

  Organic wastewater such as rice bran processing wastewater discharged from the rice bran processing factory is wastewater containing starch, protein, lipids and the like. Such organic wastewater is characterized by COD (Chemical Oxygen Demand) and BOD (Biochemical Oxygen Demand), which are indicators of organic carbon source concentration because of its high starch content. Oxygen demand) is high, and protein-derived nitrogen components are included. In addition, when producing rice oil from rice bran, there is a step of removing impurities in which phospholipids are combined with calcium, magnesium ions and the like in the purification stage. For this reason, the waste water of the refining process is characterized by containing a high concentration of phosphoric acid, and the rice bran processing waste water is a waste water in which components that are considered problematic due to water pollution are mixed at a high concentration.

In order to remove organic matter and phosphorus from the organic wastewater containing organic matter and phosphorus described above, it is necessary to add a phosphorus removal type wastewater treatment method in addition to a normal activated sludge method mainly for removing organic matter and nitrogen. However, in the activated sludge method that is generally applied, the decomposition of organic matter in the organic wastewater requires several days.
Furthermore, in rice bran processing wastewater, in the process of refining edible oil, a large amount of phosphoric acid solution is added to fats and oils in order to thoroughly remove impurities, resulting in high concentrations of phosphoric acid, which is considered a problem even in water pollution. For this reason, the removal cannot be removed only by a general activated sludge method, and the addition of a phosphorus removal type wastewater treatment method is required.

  In recent years, therefore, the A2O method has been used in sewage treatment facilities and the like as a method for simultaneously removing nitrogen and phosphorus. In the A2O method, wastewater is generally treated by partially circulating excess sludge by a microbial treatment process comprising an anaerobic process, an oxygen-free process, and an aerobic process. According to this method, phosphorus is released in the anaerobic process and phosphorus is taken up in the aerobic process by the phosphorus accumulating bacteria (PAO), and phosphorus is taken into the sludge from the wastewater to remove phosphorus in the wastewater. . On the other hand, nitrification bacteria perform nitrification in the aerobic process, and denitrification bacteria perform denitrification in the anaerobic process to remove nitrogen in the wastewater.

  Furthermore, as a technique to which this is applied, Patent Document 1 (Japanese Patent No. 4267860) proposes a method of simultaneously removing nitrogen and phosphorus using a denitrifying phosphorus accumulating bacterium (DNPAO). In this method, wastewater is treated in the order of anaerobic process, aerobic process, and anaerobic process in the presence of denitrifying phosphorus accumulating bacteria (AOA method), and an organic carbon source is supplied at the beginning of the aerobic process. It is a thing. Since denitrifying phosphorus accumulating bacteria are usually contained in sludge operated by the AOA method, it is possible to efficiently remove nitrogen and phosphorus by using wastewater conditions that can be effectively utilized.

Japanese Patent No. 4267860

According to the nitrogen / phosphorus removal type wastewater treatment process using the AOA method (microbe treatment), it is possible to simultaneously remove nitrogen and phosphorus from organic wastewater containing phosphorus. On the other hand, when organic wastewater such as rice bran processing wastewater has high COD and BOD concentrations, and there are many persistent organic substances that are difficult for microorganisms to decompose, the AOA method (microbe treatment) In the pretreatment process, organic molecules in wastewater are reduced in molecular weight by ozone microbubbles.
In this method, ozone microbubbles are brought into contact with organic waste water, and organic molecules are reduced in molecular weight by ozone as a pretreatment, thereby decomposing the hardly decomposable organic substances that cause a reduction in processing efficiency to lower the molecular weight. As a result, the organic matter, nitrogen, and phosphorus removal performance of the nitrogen / phosphorus removal type wastewater treatment process is improved as compared with the case where pretreatment with ozone microbubbles is not performed.

  However, even when the pretreatment step using ozone microbubbles is performed in the preceding stage of the nitrogen / phosphorus removal type wastewater treatment process, as shown in the rice bran processing wastewater, for example, it exhibits an acidity of pH 3 to 4, Alternatively, when the COD concentration is as high as about 6000 mg / L, the removal performance of organic substances and phosphorus is lowered or becomes unstable.

That is, if the pH of the organic wastewater to be treated is about 4 or less, the cells in the activated sludge responsible for removing organic substances and the like in the AOA method (microbe treatment) are damaged, and as a result, MLSS (Mixed Liquor described later) is damaged. Suspended Solids) concentration decreases.
In addition, in the AOA method (microbe treatment), it contains high-concentration COD, such as rice bran processing wastewater, at the time of start-up of the wastewater treatment equipment and activated sludge once the MLSS concentration falls and becomes impossible to treat. Even if wastewater having a high processing load is directly passed, the MLSS concentration does not recover while decreasing.

Here, the MLSS concentration (hereinafter also referred to as sludge concentration) is the concentration of activated sludge containing bacterial cells that perform wastewater treatment in microbial treatment, and the MLSS concentration is a constant value in order to treat organic wastewater. It is necessary to maintain the above.
MLSS is consumed for treating wastewater, but has a property of recovering as the treatment proceeds unless the COD concentration of the treated water is excessively high. However, if the MLSS concentration decreases beyond the recovery rate, further wastewater treatment becomes impossible.
Therefore, if the organic wastewater to be treated has a low pH, the MLSS concentration decreases, which causes instability in the removal process performance of organic substances and phosphorus. In addition, if the water to be treated having a high COD concentration is allowed to flow when the wastewater treatment apparatus is started up or when the MLSS concentration is lowered to an untreatable state, the MLSS concentration is not reduced and does not recover.

  In other words, simply applying the above pretreatment using ozone microbubbles to the nitrogen / phosphorus removal type wastewater treatment process allows organic wastewater with high COD concentration and high treatment load or organic wastewater with low pH to pass through. In this case, the MLSS concentration (sludge concentration) necessary for water quality treatment cannot be maintained. As a result, the removal performance of organic matter and phosphorus, that is, the wastewater treatment performance may be impaired.

  The present invention has been made in view of the above circumstances, and at least one embodiment of the present invention is an organic wastewater having a high COD concentration and / or a low pH containing a hardly decomposable organic matter such as rice bran processing wastewater. Even so, it is an object of the present invention to provide an organic wastewater treatment method and treatment apparatus capable of stably maintaining wastewater treatment performance.

An organic wastewater treatment method according to at least one embodiment of the present invention includes:
An adjustment step of adjusting the COD concentration and pH of the organic wastewater to obtain the adjusted wastewater;
A pretreatment step of supplying ozone microbubbles to the adjusted wastewater to obtain a pretreated wastewater by reducing the molecular weight of persistent organic substances in the adjusted wastewater;
Nitrogen contained in the pretreatment wastewater by subjecting the pretreatment wastewater to microbial treatment including anaerobic treatment, aerobic treatment and oxygen-free treatment in the presence of at least one of phosphorus accumulating bacteria and denitrifying phosphorus accumulating bacteria And a microbial treatment process for removing phosphorus,
An MLSS measurement step for measuring the MLSS concentration in the microorganism treatment step,
In the adjustment step, if the MLSS concentration measurement value in the MLSS measurement step is equal to or less than the threshold value, the COD concentration of the organic wastewater is equal to or less than 2000 mg / L at least until the MLSS concentration measurement value increases to the threshold value. The COD concentration of the organic wastewater is adjusted as described above, and then the pH of the organic wastewater is adjusted so that the pH of the obtained adjusted wastewater is 5.0 or more and 8.0 or less.

In the above, the MLSS concentration threshold value is such that if the MLSS concentration is equal to or higher than the threshold value, even if the COD concentration of the wastewater to be treated is high, the MLSS concentration can be recovered to restore stable treatment performance in the microbial treatment process. Concentration value.
In the organic wastewater treatment method, in the adjustment step, the COD concentration of organic wastewater that is the wastewater to be treated is adjusted to a predetermined value or less based on the measured value of the MLSS concentration. For example, when the measured value of the MLSS concentration is equal to or lower than the threshold value, when the COD concentration is as high as about 6000 mg / L, such as rice bran processing wastewater, this is diluted to 2000 mg / L or lower. For this reason, the COD of organic wastewater to be treated is reduced, and the treatment load of activated sludge in the subsequent microbial treatment process can be reduced. This makes it possible to recover the MLSS concentration (sludge concentration) afterwards, even when wastewater treatment with a high COD concentration and a high treatment load is started or when the MLSS concentration once decreases and the wastewater treatment becomes impossible. It becomes. Alternatively, the MLSS concentration can be recovered before the wastewater treatment becomes impossible. Then, by treating the organic waste water diluted at least until the MLSS concentration measurement value increases to the threshold value, the MLSS concentration can easily maintain a steady region near the threshold value. As a result, since the MLSS concentration can be stably maintained, the organic matter and phosphorus removal performance in the microbial treatment process, that is, the wastewater treatment performance can be stably maintained.
In addition, COD concentration adjustment, that is, dilution of organic wastewater is only at the start of wastewater treatment and at the start-up when the wastewater treatment performance deteriorates, and from when the MLSS concentration reaches a steady state above the threshold, Subsequent treatment is possible without diluting the wastewater. For this reason, organic matter wastewater with a high COD concentration is subjected to microbial treatment without diluting it at all, so that the wastewater treatment performance is lowered and the treatment is delayed, resulting in a reduction in organic matter removal time. As a result, aeration power in microbial treatment Can be reduced. As a result, the power cost required for wastewater treatment can be reduced.
In the organic wastewater treatment method, in the adjustment step, the pH of the organic wastewater whose COD concentration is adjusted as described above is adjusted to be 5.0 or more and 8.0 or less. For this reason, since the to-be-processed water whose pH was adjusted to 5.0 or more and 8.0 or less is passed in the subsequent microbial treatment process, the microbial cells in the activated sludge responsible for the removal of organic substances and the like in the microbial treatment process Damage received is reduced. As a result, a decrease in the MLSS concentration is suppressed, leading to stable maintenance of wastewater treatment performance in the microbial treatment process.
In this way, by providing an adjustment process that adjusts the COD concentration and pH of the organic wastewater that is the wastewater to be treated based on the measured value of the MLSS concentration, high concentration COD (carbon source) such as rice bran processing wastewater is included. In addition, it is possible to maintain a stable MLSS concentration (sludge concentration) with respect to organic wastewater having a low pH, and it is possible to improve the removal performance of organic substances, that is, the wastewater treatment performance.

In some embodiments, the microbial treatment step includes an anaerobic treatment, an aerobic treatment, and an oxygen-free treatment in this order.
In this case, the microorganism treatment step is an AOA method in which treatment is performed in the order of anaerobic treatment, aerobic treatment, and oxygen-free treatment. In some embodiments, denitrifying phosphorus-accumulating bacteria used in the microbial treatment process are mostly contained in sludge operated by the AOA method. Therefore, by effectively using this sludge, nitrogen can be removed from the wastewater to be treated. And phosphorus can be efficiently removed.

  In some embodiments, the threshold of the MLSS concentration measurement is 6500 mg / L.

  In some embodiments, the organic wastewater is rice processing wastewater or rice bran processing wastewater.

An organic wastewater treatment apparatus according to at least one embodiment of the present invention,
An organic wastewater treatment apparatus for removing organic substances and phosphorus contained in organic wastewater treatment,
COD concentration adjusting means for adjusting the COD concentration of organic waste water;
PH adjusting means for adjusting the pH of the organic waste water;
Ozone microbubble generating means for generating ozone microbubbles by dissolving ozone in microbubbles;
Pretreatment means for obtaining the treated wastewater by supplying ozone microbubbles generated by the ozone microbubble generating means to the organic wastewater to lower the molecular weight of the hardly decomposable organic matter in the organic wastewater;
In the presence of at least one of phosphorus-accumulating bacteria and denitrifying phosphorus-accumulating bacteria, connected to the subsequent stage of the pretreatment means, the pretreatment wastewater is subjected to microbial treatment including anaerobic treatment, aerobic treatment and oxygen-free treatment. Microbial treatment means for removing nitrogen and phosphorus contained in the pretreatment wastewater,
MLSS measuring means for measuring the MLSS concentration in the microorganism treatment means;
Based on the measured value of the MLSS concentration in the MLSS measurement step, a target COD concentration that is the COD concentration of the organic wastewater after being adjusted by the COD concentration adjusting means is determined, and the COD concentration of the organic wastewater is Control means for controlling the COD concentration adjusting means so as to achieve the target COD concentration.

In the organic wastewater treatment device, the COD adjusting means and the control means adjust the COD concentration of the organic wastewater that is the wastewater to be treated to a predetermined value or less based on the measured value of the MLSS concentration, and the organic wastewater by the pH adjusting means. The pH of the can be adjusted.
By controlling the COD adjusting means by the control means, the COD concentration of the organic waste water to be treated can be adjusted, thereby reducing the treatment load of activated sludge in the subsequent microbial treatment process. Therefore, even when the wastewater treatment is started or when the MLSS concentration once decreases and the wastewater treatment becomes impossible, the MLSS concentration (sludge concentration) can be recovered thereafter. Alternatively, the MLSS concentration can be recovered before the wastewater treatment becomes impossible. As a result, since the MLSS concentration can be stably maintained, the organic matter and phosphorus removal performance in the microbial treatment process, that is, the wastewater treatment performance can be stably maintained.
In addition, by adjusting the pH of the organic wastewater to be treated within a predetermined range by the pH adjusting means, it is possible to reduce damage to the cells in the activated sludge that is responsible for removing organic substances and the like in the microorganism treatment step. . As a result, a decrease in the MLSS concentration is suppressed, leading to stable maintenance of wastewater treatment performance in the microbial treatment process.
Thus, the apparatus is provided with COD adjusting means and pH adjusting means for adjusting the COD concentration and pH of the organic wastewater that is the wastewater to be treated based on the measured value of the MLSS concentration. For this reason, in the microbial treatment means in which treated water is passed after the COD adjustment means and the pH adjustment means, high-concentration COD (carbon source) such as rice bran processing wastewater and / or low pH organic wastewater In contrast, a stable MLSS concentration (sludge concentration) can be maintained. Therefore, the removal performance of organic substances, that is, the wastewater treatment performance can be improved.

  According to at least one embodiment of the present invention, wastewater treatment performance is stably maintained even with organic wastewater having a high COD concentration and / or low pH containing a hardly decomposable organic matter such as rice bran processing wastewater. be able to.

It is a flowchart which shows the organic wastewater treatment method which concerns on one Embodiment. 1 is an overall view showing a configuration example of an organic wastewater treatment apparatus according to an embodiment. It is a schematic block diagram of the COD density | concentration adjustment means and pH adjustment means of the organic wastewater treatment apparatus which concerns on one Embodiment. It is a schematic block diagram of the pretreatment tank of the organic wastewater treatment apparatus which concerns on one Embodiment. It is a test result in an Example, and is a graph which shows the time change of the MLSS density | concentration (sludge density | concentration) in the conventional processing method and the processing method of this invention. It is a test result in an Example and is a graph which shows the time-dependent change of the COD density | concentration in an aerobic process. It is the test result in an Example, and is the graph which showed the removal performance of COD density | concentration.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, and are merely illustrative examples. Only. The organic wastewater to be treated in the following embodiments is rice bran processing wastewater containing rice bran and rice broth discharged from a rice bran processing factory, etc., and is an organic wastewater containing BOD, COD, nitrogen, and phosphorus. is there.

FIG. 1 is a flowchart showing an organic wastewater treatment method according to an embodiment.
With reference to FIG. 1, the basic flow of the organic wastewater treatment method which concerns on one Embodiment of this invention is demonstrated.
The rice bran processing wastewater treatment method according to the present embodiment mainly includes an adjustment step 1, a pretreatment step 2, an anaerobic treatment step 3, an aerobic treatment step 4, and a microbial treatment step 6 including an oxygen-free treatment step 5. MLSS measurement step 7. This treatment method may further include a solid-liquid separation step 8 for separating the treated water and excess sludge obtained in the microorganism treatment step after the microorganism treatment step 6.

  Next, each step of the organic wastewater treatment method according to an embodiment will be described.

  In the adjustment step 1, the adjustment wastewater is obtained by adjusting the COD concentration and pH of the organic wastewater to be treated. In the adjustment step 1, if the MLSS concentration measurement value in the MLSS measurement step 7 described later is equal to or less than the threshold value, the COD concentration of the organic waste water is adjusted so that the COD concentration of the organic waste water to be treated is 2000 mg / L or less. The concentration is adjusted, and then the pH of the organic wastewater is adjusted so that the pH of the obtained adjusted wastewater is 5.0 or more and 8.0 or less.

The adjustment of the COD concentration is performed by diluting raw rice bran processing water (organic wastewater) based on the MLSS concentration measurement value in the MLSS measurement step 7. That is, if the MLSS concentration is equal to or lower than the threshold value, the COD concentration is adjusted by diluting the organic waste water with water at least until the MLSS concentration measurement value reaches the threshold value. On the other hand, if the MLSS concentration is higher than the threshold value, the COD concentration adjustment by dilution is not performed.
In one embodiment, the organic wastewater is diluted with water such that the COD concentration is 2000 mg / L or less. When the COD concentration is about 2000 mg / L or less, even if the MLSS concentration is reduced and the wastewater treatment performance in the microbial process 6 is reduced, the treatment load of sludge is at least temporarily reduced because the COD concentration is suppressed. To do. For this reason, it is possible to recover (increase) the lowered MLSS concentration.
In one embodiment, the threshold for MLSS concentration is 6500 mg / L. In another embodiment, the threshold value for MLSS concentration is adjusted in the range of 5000 mg / L to 7000 mg / L.
In another embodiment, in addition to the COD concentration adjustment based on the MLSS concentration measurement value, the COD concentration may be adjusted at the start of the organic wastewater treatment. At the start of wastewater treatment, the sludge treatment load in the microbial process 6 is large. Therefore, the MLSS concentration is easily recovered by diluting the organic wastewater to reduce the COD concentration, and the wastewater treatment performance in the microbial treatment process 6 is maintained. It becomes easy to be done.
In another embodiment, the COD concentration after adjusting the COD concentration is 1500 mg / L or less.

Further, the pH of the organic wastewater is adjusted so that the pH becomes 5.0 or more and 8.0 or less by adding a 40% by mass aqueous sodium hydroxide solution after adjusting the COD concentration. When the pH is adjusted in this way, water to be treated whose pH is adjusted to about 5.0 to 8.0 in the subsequent microbial treatment step is passed, so that organic substances and the like are removed in the microbial treatment step. Damage to the cells in the activated sludge is reduced. As a result, a decrease in the MLSS concentration is suppressed, leading to stable maintenance of wastewater treatment performance in the microbial treatment process.
In another embodiment, the pH is adjusted to be 6.0 or more and 7.0 or less.

In the pretreatment step 2, ozone microbubbles in which ozone is dissolved in the microbubbles are supplied to the rice bran processing wastewater (adjusted wastewater) adjusted in COD concentration and pH in the adjustment step 1, and the hard decomposition contained in the adjusted wastewater To reduce the molecular weight of organic substances and obtain pretreatment wastewater.
The microbubble is a fine bubble having a size (diameter) of about 10 to several tens of μm, and preferably a bubble having a size smaller than 50 μm when the bubble is generated. By supplying ozone microbubbles to the adjusted wastewater, the molecular weight of persistent organic substances in the adjusted wastewater is reduced, and the organic matter is easily taken up by phosphorus accumulating bacteria and denitrified phosphorus accumulating bacteria by anaerobic treatment. .

More specifically, the molecular weight of the hardly decomposable organic substance in the adjusted wastewater is reduced by the oxidizing power of ozone, and the molecular weight of the hardly decomposable organic substance is reduced by the oxidizing power of the OH radical generated by the disappearance of the microbubbles. At this time, it is considered that the molecular weight of the hardly decomposable organic substance is promoted by the charge of the microbubbles. Furthermore, since the microbubbles are ultrafine, the rising speed is assumed to substantially follow the Stokes equation, and the rising speed of the microbubbles is very slow. Accordingly, since the microbubbles stay in the liquid for a long time, the contact efficiency between the hardly-decomposable organic substance and ozone or OH radicals becomes extremely high, and it becomes possible to reduce the molecular weight of the hardly-decomposable organic substance with high efficiency.
In addition, it is preferable to perform preliminary treatments such as removing impurities in the wastewater to be treated or adjusting the temperature of the wastewater in the previous stage of the pretreatment step.

In the microorganism treatment step 6 of the present embodiment, a microorganism treatment including anaerobic treatment, aerobic treatment, and oxygen-free treatment in this order in the pretreatment wastewater obtained in the pretreatment step 2 in the presence of denitrifying phosphorus-accumulating bacteria. To remove nitrogen and phosphorus contained in the pretreatment wastewater.
In another embodiment, the microbial treatment may be performed in the presence of phosphorus accumulating bacteria instead of denitrifying phosphorus accumulating bacteria, or in the presence of phosphorus accumulating bacteria and denitrifying phosphorus accumulating bacteria.
In another embodiment, the microbial treatment includes anaerobic treatment, aerobic treatment, and anoxic treatment in any order.

In the anaerobic treatment step 3, the pretreatment wastewater obtained in the pretreatment step 2 is anaerobically treated in the presence of at least one of phosphorus accumulating bacteria and denitrifying phosphorus accumulating bacteria. Here, the phosphorus accumulating bacteria and the denitrifying phosphorus accumulating bacteria take up the carbon source (organic matter) contained in the pretreated wastewater and release phosphorus. At this time, since the hard-to-decompose organic matter in the rice bran processing wastewater (conditioned wastewater) is reduced in the pretreatment step 3, the carbon source can be smoothly taken up in the anaerobic treatment.
Preferably, in the anaerobic treatment step, sludge (activated sludge) containing at least one of phosphorus accumulating bacteria and denitrifying phosphorus accumulating bacteria or a biofilm on which at least one of them is immobilized is used.

  When anaerobic treatment is mainly performed using sludge containing denitrifying phosphorus-accumulating bacteria, the sludge containing denitrifying phosphorus-accumulating bacteria is acclimatized under anaerobic / anoxic conditions, and the denitrifying phosphorus-accumulating bacteria are favored. Fortune-telling. In this acclimatization, a nitrate ion source such as sodium nitrate may be appropriately added at the end of the anaerobic treatment depending on the activity state of the microorganism, and each treatment is preferentially performed by denitrifying phosphorus-accumulating bacteria while supplying adjusted wastewater to be treated. It is preferable to repeat these processes until they are occupied. Mainly, when anaerobic treatment is performed using a biofilm on which denitrifying phosphorus-accumulating bacteria are immobilized, nitrifying bacteria with a slow growth rate are placed inside the biofilm, and denitrifying phosphorus-accumulating bacteria are placed outside the biofilm. It is preferable to use a biofilm that can be localized.

  In the aerobic treatment step 4, air is supplied into the conditioned wastewater to be treated to obtain an aerobic condition, where oxidation of ammonia nitrogen to nitrate nitrogen by nitrifying bacteria and uptake of phosphorus by phosphorus accumulating bacteria are performed. Is called. In this aerobic treatment step 4, in order to prevent excessive phosphorus uptake by phosphorus accumulating bacteria, it is preferable to add a small amount of an organic carbon source at the initial stage of the aerobic treatment step to limit the phosphorus uptake amount. This makes it possible to sufficiently take up nitrate nitrogen by the denitrifying phosphorus-accumulating bacteria in the subsequent oxygen-free treatment step 5.

In the oxygen-free treatment step 5, the supply of air is stopped to make oxygen-free conditions, where denitrification reaction and phosphorus uptake by denitrifying phosphorus-accumulating bacteria are performed.
After the end of the oxygen-free treatment step 4, a solid-liquid separation step 8 for separating excess sludge and treated water is performed. In the solid-liquid separation step 8, for example, a known method such as precipitation or membrane separation is used, and a flocculant may be added to coagulate and precipitate sludge.

The above-described microorganism treatment step 6 may be a batch type or a continuous type. In the case of a continuous type, it is preferable to return a part of the excess sludge separated in the solid-liquid separation step 8 to the anaerobic treatment step 3 to maintain the MLSS concentration.
According to this embodiment, by providing the adjustment process 1 before the pretreatment process 2 and the microorganism treatment process 6, the wastewater treatment performance in the microorganism treatment process is maintained, thereby improving the phosphorus removal performance. Can be expected. Thereby, the phosphorus density | concentration in the sludge used for a microorganism treatment process becomes high, and when the conventional method of collect | recovering phosphorus from sludge is employ | adopted, the improvement of a phosphorus collection | recovery rate can be anticipated.

In the MLSS measurement step 7, the MLSS concentration in the microorganism treatment step 6 is measured. The MLSS concentration is the amount of activated sludge in the aeration tank in the activated sludge method expressed in mg / L. In this embodiment, the pretreatment waste water to be treated in the microorganism treatment step 6 and the microorganism treatment step 6 are used. It is the density | concentration (mg / L) of the sludge in a liquid mixture with the sludge (active sludge) containing at least one of phosphorus accumulation bacteria and denitrification phosphorus accumulation bacteria.
A commonly used MLSS meter can be used to measure the MLSS concentration.

  Next, with reference to FIGS. 2-4, the structure of the organic waste water treatment apparatus which concerns on one Embodiment is demonstrated.

FIG. 2 is an overall view showing a configuration example of an organic wastewater treatment apparatus according to an embodiment, and FIG. 3 is a schematic configuration diagram of COD concentration adjusting means and pH adjustment means of the organic wastewater treatment apparatus according to one embodiment. It is.
As shown in FIG. 2, the organic wastewater treatment apparatus 110 mainly includes a COD concentration adjusting means 50, a pH adjusting means 60, an ozone microbubble generating means 11, a pretreatment means including a pretreatment tank 10, A microbial treatment means including a microbial treatment tank 35, an MLSS measurement means including an MLSS meter 56, and a control means including a controller 100 are provided. The microbial treatment tank 35 may be provided with a plurality of tanks for performing the anaerobic treatment process, the aerobic treatment process, and the anaerobic treatment process separately, and these may be connected in series, as shown in FIG. The anaerobic treatment process, the aerobic treatment process, and the anaerobic treatment process may be performed in a single tank by changing the conditions. However, since the installation area of the apparatus can be reduced and the apparatus can be reduced in size, A tank is preferred.

Below, the detailed structure of an organic wastewater treatment apparatus is demonstrated.
The organic waste water to be treated is temporarily stored in the water storage tank 21 by the pump 20. The water storage tank 21 is provided with a sensor 22 for measuring the pH and temperature of organic wastewater.
Rice processing wastewater in the water storage tank 21 is fed to the pretreatment tank 10 by a pump 24 through a wastewater supply line 23. A valve 25 is provided on the wastewater supply line 23, and the amount of wastewater supplied to the pretreatment tank 10 is adjusted by the valve 25. A return line 26 for returning a part of the waste water branched from the waste water supply line 23 to the water storage tank 21 may be provided, and the amount of waste water returned is adjusted by a valve 27.

The pretreatment tank 10 is supplied with ozone microbubbles generated by the ozone microbubble generating means 11. Specifically, a circulation line 17 (17a, 17b) is connected to the ozone microbubble generating means 11, and the organic waste water fed to the pretreatment tank 10 is the circulation line 17 (17a, 17b). By circulating between the pretreatment tank 10 and the microbubble generator 16 through the ozone microbubbles are supplied to the wastewater. Valves 18 (18a, 18b) are provided on the circulation line 17 (17a, 17b), and the amount of circulation is adjusted here. In addition, the ozone microbubble production | generation means 11 is the same as what was demonstrated in FIG.
The pretreatment tank 10 includes a stirrer 19 for stirring the inside of the tank, an ozone monitor 28 for measuring the ozone concentration in the wastewater in the pretreatment tank 10, and a sensor 29 for measuring the pH and temperature of the organic wastewater. Is installed.

The organic waste water discharged from the pretreatment tank 10 is fed to the microorganism treatment tank 35 by the pump 31 through the waste water supply line 30. A valve 32 and the like are provided on the waste water supply line 30, and the amount of waste water to be supplied to the microorganism treatment tank 35 is adjusted by the valve 32 and the like.
A microbubble generator 36 is connected to the microorganism treatment tank 35 via a circulation line 37 (37a, 37b). The microbubble generator 36 is an apparatus for supplying microbubbles of air into wastewater to make the inside of the microorganism treatment tank 35 aerobic. The supply amount of air (aeration amount) is adjusted by the valve 38 (38a, 38b).

The microorganism treatment tank 35 is connected with an air cooling chiller 40 for adjusting the temperature in the tank via a circulation line 41 (41a, 41b), and the circulation line 41a is an expansion tank for preventing pressure pulsation. 43 is connected.
Further, the microorganism treatment tank 35 is provided with a stirrer 44 for stirring the inside of the tank and a sensor 45 for measuring the pH and temperature of waste water in the microorganism treatment tank.

In the microorganism treatment tank 35 having the above-described configuration, it is preferable to change the state of the tank by adjusting the opening of each valve in accordance with the conditions of each treatment process. For example, in the aerobic treatment process, the valve 38 (38a, 38b) of the microbubble generator 36 is opened to supply microbubbles of air into the microorganism treatment tank 35 to obtain an aerobic condition. Moreover, when adjusting temperature, the valve | bulb 42 (42a, 42b) of the air cooling chiller 40 is adjusted.
When a series of treatment steps including an anaerobic treatment step, an aerobic treatment step, and an anaerobic treatment step are completed in the microbial treatment tank 35, the treated water is discharged from the discharge line 70, and a subsequent solid-liquid separation device (not shown). ).

  Data of measured values of pH and temperature measured by sensors 22, 29, and 45 installed in the water storage tank 21, the pretreatment tank 10, and the microorganism treatment tank 35 are transmitted to the controller 100 described later.

In one embodiment, the COD concentration adjusting means 50 for adjusting the COD concentration of the waste water to be treated is connected to the water storage tank 21. In one embodiment, as shown in FIGS. 2 and 3, the COD concentration adjusting means 50 includes a dilution water tank 52 that stores dilution water for diluting the COD concentration of wastewater to be treated in the water storage tank 21, and Dilution water flow control valve 54. The amount of dilution water supplied from the dilution water tank 52 to the water storage tank 21 is controlled by the open / close state of the dilution water flow rate control valve 54. The open / close state of the dilution water flow control valve 54 is controlled by a controller 100 described later.
In another embodiment, the COD concentration adjusting means 50 including the dilution water tank 21 and the dilution water flow rate control valve 54 is connected to the pretreatment tank 10 so as to dilute the wastewater to be treated supplied to the pretreatment tank 10. May be configured.

A pH adjusting means 60 for adjusting the pH of waste water to be treated is connected to the pretreatment tank 10. In one embodiment, as shown in FIG. 2 and FIG. 3, the pH adjusting means 60 includes a pH adjusting agent tank 62 for storing a pH adjusting agent for adjusting the pH of waste water to be treated, and a pH adjustment. A pH adjusting pump 64 for delivering the pH adjusting agent in the agent tank 62 into the pretreatment tank 10. When the controller 100 described later controls the pH adjustment pump 64, the amount of the pH adjusting agent delivered from the pH adjustment pump 64 into the pretreatment tank 10 is controlled.
As the pH adjustment pump 64, for example, an electromagnetic metering pump can be used. As the pH adjuster, an acidic aqueous solution can be used for alkaline treated wastewater, and a basic aqueous solution can be used for acidic treated wastewater. In one embodiment, in order to increase the pH of rice bran processing wastewater (organic wastewater) having a low pH, a 40% by mass aqueous sodium hydroxide solution is used as a pH adjuster.

  In some embodiments, the adjustment of the COD concentration and pH of the wastewater to be treated by the COD concentration adjusting means 50 and the pH adjusting means 60 is also affected by the temperature in the microbial treatment tank 35. The temperature in 35 is adjusted to 30 to 35 ° C. by a chiller 40 or the like that can be cooled or adjusted for heating according to need.

  An MLSS meter 56 for measuring the MLSS concentration in the microorganism treatment tank is connected to the microorganism treatment tank 35. The data of the MLSS measurement value measured by the MLSS meter 56 is transmitted to the controller 100.

The controller 100 is configured to measure pH and temperature values transmitted from the sensors 22, 29, and 45 installed in the water storage tank 21, the pretreatment tank 10, and the microorganism treatment tank 35, and MLSS measurement transmitted from the MLSS meter 56. Value data is received, and the COD concentration adjusting means 50 and the pH adjusting means 60 are controlled based on these values.
For example, when the MLSS measurement value acquired by the controller 100 is equal to or less than a preset threshold, the amount of dilution is such that the COD concentration of the wastewater to be treated in the water storage tank 21 is equal to or less than a certain value (for example, 2000 mg / L). The dilution water flow control valve is controlled so that water is sent from the dilution water tank 52 to the water storage tank 21. And it controls so that a to-be-processed wastewater is diluted as mentioned above during the period until MLSS measurement value becomes a fixed value (for example, 7000 mg / L).
For example, when the pH transmitted from the sensor 29 installed in the pretreatment tank 10 to the controller 100 is outside a certain range (for example, 5.0 or more and 8.0 or less), the pH is within the above range. The pH adjusting pump 64 is controlled so that the pH adjusting agent stored in the pH adjusting agent tank 62 is fed into the pretreatment tank 10 by an amount necessary for the above.

FIG. 4 is a schematic configuration diagram illustrating a pretreatment tank of an organic wastewater treatment apparatus according to an embodiment.
Ozone microbubbles are supplied to the pretreatment tank 10 from the ozone microbubble generating means 11.
The ozone microbubble generating means 11 generates an oxygen concentrator 12 that inhales air to generate high-concentration oxygen, an ozone generator 13 that generates ozone from oxygen, and ozone microbubbles in which ozone is dissolved in microbubbles. And a microbubble generator 16. Note that the ozone microbubble generating means 11 is shown as a gas-liquid mixing pump type as an example in the figure, but is not limited to this, and may be another type such as a swirling nozzle type, or ozone from air. It may be a means to generate.

Oxygen discharged from the oxygen concentrator 12 (preferably an oxygen concentration of 90% or more) is supplied to the ozone generator 13 where ozone is generated using oxygen as a raw material. This ozone is supplied from the ozone generator 13 to the microbubble generator 16 through the ozone supply line 14. At this time, the ozone flow rate is adjusted by the flow rate adjustment valve 15 on the ozone supply line 14.
The pretreatment tank 10 and the microbubble generator 16 are connected by a circulation line 17 (17a, 17b), and rice bran processing wastewater circulating on the circulation line 17 (17a, 17b) is converted into ozone by the microbubble generator 16. The supply of microbubbles reduces the molecular weight of persistent organic substances in wastewater.
Thus, by circulating the wastewater while supplying the ozone microbubbles to the rice bran processing wastewater, the contact efficiency between the rice bran processing wastewater and the ozone microbubbles is improved, and the processing time can be shortened.

In the pretreatment tank 10, in addition to the above-described configuration, ozone microbubbles may be supplied from an aeration tube (not shown) provided at the bottom of the tank, or a stirring means is provided in the tank to provide ozone microbubbles. The contact efficiency between the bubble and the rice processing wastewater may be further improved.
The rice bran processing wastewater discharged from the pretreatment tank 10 is supplied to the subsequent microorganism treatment tank 35 as pretreated wastewater that has been pretreated.

[Example 1]
As Example 1, the test which investigates the time-dependent change of MLSS density | concentration in the process of rice bran processing wastewater was done.
Using the organic wastewater treatment apparatus shown in FIG. 2, without adjusting the COD concentration and pH in the adjustment step, the raw rice bran processing wastewater remains the same as the pretreatment step and the microorganism treatment step under the conditions shown below. A gas step was performed. The COD concentration before adjustment was about 6000 mg / L.
In this method, the adjustment process which adjusts COD density | concentration and pH was added in the tank, and the pre-processing was performed on the conditions similar to the above.
In the said adjustment process, when the measured value of MLSS density | concentration in a microorganism treatment process is 6500 mg / L or less, until the MLSS density | concentration measured value becomes 7000 mg / L, the raw | natural water of rice bran processing wastewater is 2000 mg / L or less COD density | concentration The COD concentration was adjusted by dilution. After adjusting the COD concentration, the pH was adjusted to 6.5 using a 40% by mass aqueous sodium hydroxide solution.
<Conditions in pretreatment process>
Oxygen inflow from the oxygen concentrator 12 to the ozone generator 13: 1 [L / min] (oxygen concentration 90% or more)
Ozone generation amount of the ozone generator 13: 9.66 [g / h] (161 [mg / min])
Ozone concentration: 161 [g / nm ³ ]
Microbubble circulation rate: 24.5 [L / min]
Reaction time of wastewater to be treated and ozone microbubbles in the pretreatment tank 10: 90 minutes

The conventional treatment method in which the pretreatment step and the microorganism treatment step are performed without performing the adjustment step from the start of treatment until 30 days have elapsed, and the change in MLSS concentration over time when the above treatment is carried out after 30 days have elapsed. The results are shown in FIG.
The MLSS concentration of about 3400 mg / L is initially temporarily from the start of the treatment in which the conventional treatment method in which the pretreatment step and the microorganism treatment step are performed without adjusting the pH and the COD concentration until 30 days have elapsed. Although it increased, it fell below 2000 mg / L in 29 days, and it became unprocessable and did not recover (increase) any more. For this reason, in wastewater with a high COD concentration of about 6000 mg / L, treatment with sludge in the microbial treatment process cannot withstand the load of rice bran processing wastewater, resulting in reduced treatment performance and a reduction in MLSS concentration (sludge concentration). I found out that it was also connected.
Thereafter, when switching to the treatment method of the present invention with an adjustment step added, the MLSS concentration of about 3600 mg / L initially shows a gradual increasing tendency, 6300 mg / L after 80 days, and 7000 mg / L after 117 days. Increased to L. From this, it was found that the MLSS concentration can be maintained at about 7000 mg / L by adding the treatment method of the present invention to which an adjustment step is added, and the sludge concentration that can correspond to the high concentration COD wastewater can be maintained.

[Example 2]
As Example 2, the test which investigates the time-dependent change of the COD density | concentration of rice bran processing wastewater was done.
The organic wastewater treatment apparatus shown in FIG. 2 was used to perform the adjustment step and the pretreatment step under the following conditions, followed by an anaerobic treatment for 4 hours, followed by an aerobic treatment. Under aerobic treatment, the change over time in the COD concentration of the wastewater to be treated was measured. In the adjustment step, the test was performed by changing the diluted COD concentration. In addition, the anaerobic process and the aerobic process were performed by the continuous type.

<Conditions in the adjustment process>
COD concentration after the adjustment process (initial COD concentration):
7440, 6160,
13 types of 5200, 5120, 3840, 3000, 2260, 1880, 1600, 1250, 1110, 740, 280 (mg / L) pH after adjustment step: 6.5 (using 40 mass% sodium hydroxide aqueous solution) Adjustment)
<Conditions in pretreatment process>
Oxygen inflow from the oxygen concentrator 12 to the ozone generator 13: 1 [L / min] (oxygen concentration 90% or more)
Ozone generation amount of the ozone generator 13: 9.66 [g / h] (161 [mg / min])
Ozone concentration: 161 [g / nm ³ ]
Microbubble circulation rate: 24.5 [L / min]
Reaction time of wastewater to be treated and ozone microbubbles in the pretreatment tank 10: 90 minutes

The measurement result of the time-dependent change of COD density | concentration of rice bran processing wastewater is shown in FIG.
In FIG. 6, the horizontal axis indicates the elapsed time (unit: time) after the start of the aerobic treatment, and the vertical axis indicates the COD concentration (unit: mg / L).
In rice bran processing wastewater adjusted to COD concentrations of 280, 740, 1110, 1250, 1600, and 2260 (mg / L) in the adjustment step, the COD concentration decreases by 90% or more in 15 to 36 hours from the start of aerobic treatment. I was able to.
On the other hand, in the adjustment process, the rice bran processing wastewater prepared with COD concentrations of 1880, 3000, 3840, 5120, 5200, 6160, 7440 (mg / L), respectively, from the initial concentration even after 5 hours from the start of the aerobic treatment However, the COD concentration did not decrease.
According to this result, it was found that by adjusting the COD concentration to about 2000 mg / L or less in the adjustment step, the COD concentration decreases smoothly in the subsequent microbial treatment, and the treatment performance in the microbial treatment step is maintained. .

[Example 3]
As Example 3, the COD concentration after microbial treatment of rice bran processing wastewater adjusted by diluting the COD concentration was confirmed.
For the rice bran processing wastewater prepared using the organic wastewater treatment apparatus shown in FIG. 2 and having a COD concentration of 1800 to 2500 mg / L after the adjustment step, the adjustment step (pH adjustment) and pretreatment are performed under the same conditions as in Example 2 above. After performing the process, the microorganism treatment process was performed under the following conditions. The microbial treatment process was performed continuously.
<Processing time for each process of microbial treatment>
Anaerobic treatment: 4 hours Aerobic treatment: 26 hours Anaerobic treatment: 3 hours

  The measurement results of the COD concentration before and after the microorganism treatment are shown in FIG. As a result, it was found that the COD concentration after the microbial treatment process decreased by 90% or more. Thereby, it turned out that high carbon source (organic matter) processing performance is obtained by using the processing method and processing device concerning one embodiment of the present invention.

DESCRIPTION OF SYMBOLS 1 Adjustment process 2 Pretreatment process 3 Anaerobic treatment process 4 Aerobic treatment process 5 Oxygen treatment process 6 Microbial treatment process 7 MLSS measurement process 8 Solid-liquid separation process 10 Pretreatment tank 11 Ozone microbubble production | generation means 12 Oxygen concentrator 13 Ozone generator 16 Microbubble generator 35 Microbial treatment tank 50 COD concentration adjusting means 56 MLSS meter 60 pH adjusting means 62 pH adjusting agent tank 64 pH adjusting pump 100 Controller 110 Organic waste water treatment apparatus

Claims (6)

An adjustment step of adjusting the COD concentration and pH of the organic wastewater to obtain the adjusted wastewater;
A pretreatment step of supplying ozone microbubbles to the adjusted wastewater in the pretreatment tank to obtain a pretreated wastewater by depolymerizing the hardly decomposable organic matter in the adjusted wastewater;
In the microbial treatment tank provided in the subsequent stage of the pretreatment tank, anaerobic treatment, aerobic treatment and oxygen-free treatment are performed on the pretreatment wastewater in the presence of at least one of phosphorus accumulating bacteria and denitrifying phosphorus accumulating bacteria. A microbial treatment step of performing microbial treatment including removing nitrogen and phosphorus contained in the pretreatment wastewater;
An MLSS measurement step for measuring the MLSS concentration of the microorganism treatment tank in the microorganism treatment step, and an organic wastewater treatment method comprising:
In the adjustment step, when the MLSS concentration measurement value of the microorganism treatment tank in the MLSS measurement step is larger than the threshold value , the COD concentration of the organic waste water is not adjusted, and the MLSS concentration measurement value is equal to or less than the threshold value . If present, at least the period until the MLSS concentration measurement value increases to the threshold value, the COD concentration of the organic waste water is such that the COD concentration of the organic waste water is 2000 mg / L or less on the upstream side of the pretreatment tank. And then adjusting the pH of the organic wastewater so that the pH of the obtained adjusted wastewater is 5.0 or more and 8.0 or less ,
In the adjustment step,
Adjusting the COD concentration of the organic wastewater by diluting the organic wastewater in the water storage tank located on the front side of the pretreatment tank with dilution water;
An organic wastewater treatment method for adjusting the pH of the adjusted wastewater by adding a pH adjuster to the adjusted wastewater in the pretreatment tank .   The organic wastewater treatment method according to claim 1, wherein the microorganism treatment step includes anaerobic treatment, aerobic treatment, and oxygen-free treatment in this order.   The organic wastewater treatment method according to claim 1 or 2, wherein the threshold value of the MLSS concentration measurement value is 6500 mg / L.   The organic wastewater treatment method according to any one of claims 1 to 3, wherein the organic wastewater is rice processing wastewater or rice bran processing wastewater. The organic wastewater treatment method according to any one of claims 1 to 4, wherein the pH adjuster is an aqueous sodium hydroxide solution . An organic wastewater treatment device for removing nitrogen and phosphorus contained in organic wastewater treatment,
COD concentration adjusting means for adjusting the COD concentration of organic waste water;
PH adjusting means for adjusting the pH of the organic waste water;
Ozone microbubble generating means for generating ozone microbubbles by dissolving ozone in microbubbles;
Pretreatment means for obtaining pretreatment wastewater by supplying ozone microbubbles generated by the ozone microbubble generation means to the organic wastewater in the pretreatment tank to lower the molecular weight of persistent organic substances in the organic wastewater. When,
In the microbial treatment tank provided in the subsequent stage of the pretreatment tank, anaerobic treatment, aerobic treatment and oxygen-free treatment are performed on the pretreatment wastewater in the presence of at least one of phosphorus accumulating bacteria and denitrifying phosphorus accumulating bacteria. Microbial treatment means for performing microbial treatment including removing nitrogen and phosphorus contained in the pretreatment wastewater;
MLSS measurement means for measuring the MLSS concentration in the microorganism treatment tank of the microorganism treatment means;
When the measured value of the MLSS concentration of the microorganism treatment tank is larger than the threshold value, the COD concentration of the organic waste water is not adjusted. When the measured value of the MLSS concentration is equal to or lower than the threshold value , at least the measured MLSS concentration value During the period until the threshold value increases to the threshold value, the COD concentration adjusting means is controlled so that the COD concentration of the organic waste water is 2000 mg / L or less on the upstream side of the pretreatment tank, and the adjustment of the COD concentration Control means for controlling the pH adjusting means so that the pH of the adjusted waste water obtained by the method is adjusted to 5.0 or more and 8.0 or less ,
The COD concentration adjusting means is configured to adjust the COD concentration of the organic waste water by diluting the organic waste water in a water storage tank located on the upstream side of the pretreatment tank with dilution water,
The organic wastewater treatment apparatus , wherein the pH adjusting means is configured to adjust the pH of the adjusted wastewater by adding a pH adjuster to the adjusted wastewater in the pretreatment tank .

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