JP6490114B2 - Biological treatment method of organic wastewater - Google Patents

Description

  The present invention relates to a biological treatment method for organic wastewater.

  The applicant has already achieved the reduction of excess sludge by incorporating the activated sludge solubilization process in the treatment of wastewater using the activated sludge method, and it is discharged at the final stage compared to the conventional treatment method. The cost of sludge treatment can be reduced by drastically reducing the moisture content of sludge that ultimately needs treatment without causing deterioration of treated water and without complicating the expansion of the equipment and the treatment flow. A biological treatment method of organic wastewater that can be significantly reduced and is economical and excellent in terms of protecting the global environment has been proposed (Patent Documents 1 and 2). Moreover, the proposal about the method of solubilizing an excess sludge efficiently is also made (patent document 3).

Japanese Patent No. 5951986 Japanese Patent No. 5951984 JP 2000-61488 A

  However, according to the study by the present inventors, the amount of excess sludge can be greatly reduced by the biological treatment method of organic wastewater provided with a process for solubilizing excess sludge. When applied, it was found that the phosphorus concentration of the treated water tends to increase.

  Here, as a method for reducing the phosphorus concentration of the activated sludge treated water, a metal compound such as an iron salt solution or an aluminum salt solution is added to the activated sludge aeration tank or the inlet of the final sedimentation basin to make phosphate ions sparingly soluble. It is fixed in activated sludge as a metal compound such as iron phosphate or aluminum phosphate, and is pulled out of the system together with excess sludge.

  However, in the method of performing the operation that reduces or eliminates excess sludge discharge, provided with a process for solubilizing excess sludge as described above, phosphorus fixed in the activated sludge cannot be discharged out of the system and discharged. In this case, the activated sludge is also drawn out together with the fixed phosphorus, and the purpose of reducing excess sludge cannot be achieved.

  Therefore, an object of the present invention is to provide a problem in a simple and economical method for treating organic wastewater that can significantly reduce the amount of excess sludge provided with a process for solubilizing excess sludge by a simple method. An object of the present invention is to provide a biological treatment method for organic wastewater that can effectively suppress the tendency of increasing the phosphorus concentration of treated water by a simple method.

  The above object is achieved by the present invention described below. That is, the present invention is an activated sludge treatment method in which organic waste water is used at least using a first sedimentation tank, an activated sludge treatment tank, and a final sedimentation tank. A solubilization treatment step for solubilizing a part or all of the solution is provided, and in the solubilization treatment step, phosphate ions are added to the sludge being solubilized or to the sludge after the solubilization treatment. Provided is a biological treatment method for organic wastewater, characterized in that after solubilizing and / or insolubilizing substances are added, the solubilized sludge is first returned to the settling tank.

  As a preferred form of the biological treatment method of the organic wastewater of the present invention, the organic wastewater is sewage; the substance that adsorbs and / or insolubilizes the phosphate ion is insoluble or bound to the phosphate ion. It is a metal or a metal salt that forms a hardly soluble salt; and the substance that adsorbs and / or insolubilizes the phosphate ions is any one selected from the group consisting of aluminum or iron and salts thereof. It is done.

  According to the present invention, in a simple and economical organic wastewater treatment method, the amount of surplus sludge provided with a step of solubilizing surplus sludge can be greatly reduced by a simple method. Although it is a method, the biological treatment method of the organic wastewater which can suppress effectively that the phosphorus concentration of treated water raises is provided.

It is a flowchart which shows the processing method of this invention of the form which extracts a part of excess sludge. It is a flowchart which shows the processing method of this invention of the form which does not draw out excess sludge and all solubilizes. It is a flowchart which shows the processing method of this invention of the form which introduce | transduced the system which processes the deposit from an initial sedimentation tank with an anaerobic digester into the flow of FIG. FIG. 3 is a flowchart of processing of a processing method according to the first embodiment. It is a flowchart of a process of the processing method of Example 2. 10 is a flowchart of processing of a processing method of Comparative Example 1. FIG. 10 is a flowchart of processing of a processing method of Comparative Example 2. FIG. FIG. 10 is a flowchart of processing of a processing method according to the third embodiment.

  Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. When the above-described biological treatment method for organic wastewater provided with a step of solubilizing excess sludge is applied to the treatment of actual organic wastewater such as sewage, the present inventors have set the phosphorus concentration of the treated water. As a result of intensive investigations on the cause of the increase in the number of nuclei and further studies based on the obtained knowledge, the present invention has been achieved.

  First, the reason why the phosphorus concentration of the treated water tends to increase in the above treatment is considered as follows. When the excess sludge is solubilized, phosphorus in the sludge is also solubilized, so when the sludge solubilized is first returned to the settling tank and treated, the solubilized phosphorus is, for example, treated in the treatment object. It elutes into some sewage, and as a result, the phosphorus concentration of the sewage at the outlet of the first sedimentation tank increases. For this reason, sewage with high phosphorus concentration flows into the activated sludge treatment tank (hereinafter also referred to as “aeration tank”) as raw water, and the phosphorus concentration of the treated water at the final sedimentation tank outlet after the aeration tank increases. It is thought that it will be.

Here, as a method for suppressing the increase in the phosphorus concentration of the final treated water, there are the following methods.
1. A method of suppressing an increase in the phosphorus concentration of treated water by adding a metal compound such as an aluminum salt to an aeration tank or a final sedimentation tank and fixing phosphorus in activated sludge.
2. A method in which a metal compound such as an aluminum salt is added to the inlet of the first sedimentation tank, phosphorus in the sewage is fixed as a metal salt, and the sedimentation is separated in the first sedimentation tank.

  However, these methods have the following problems. First, the above-described 1. In the case of this method, metal phosphate and metal hydroxide in which phosphorus is fixed accumulate in the activated sludge of the aeration tank. And the discharge | release of the phosphorus outside a system is discharged | emitted as the excess sludge separated into solid and liquid by the final sedimentation tank. The concentration ratio of the added aluminum salt or the like to the aeration tank is equal to the ratio obtained by dividing the total sludge amount present in the aeration tank and the final sedimentation tank by the amount of discharged sludge, that is, sludge residence time (SRT). . Specifically, when 3 mg / l is added in terms of aluminum element, 45 mg / l of aluminum is present in the aeration tank when the SRT is 15 days. For this reason, the following problems arise.

  First, when the metal salt in which phosphorus is fixed and sludge in which metal hydroxide is accumulated are solubilized, the metal is re-dissolved by the solubilization process. As a result, the amount of electric power or chemicals required for the solubilization process is greatly increased, which is a major factor in increasing the cost required for the solubilization process. Second, metals such as aluminum are inactive as activated sludge and may inhibit the activity of activated sludge microorganisms.

  2. As described above. In the case of this method, there are the following problems. In this method, it is necessary to control the injection amount of the metal salt and the like while accurately grasping the concentration (amount) of phosphorus at the beginning of the precipitation tank. However, the amount of sewage that flows into the settling tank and the concentration of phosphorus greatly fluctuate even during the day, and the amount of sludge that has been solubilized is not always constant and is discharged intermittently. There are many, and it is difficult to grasp the concentration (amount) of phosphorus accurately. If the concentration (amount) of phosphorus cannot be accurately grasped, the following problems arise. That is, if a metal salt or the like is injected quantitatively without knowing the exact phosphorus concentration (amount), the metal salt becomes excessive and insufficient, and phosphorus cannot be removed properly. First, when it is insufficient, the phosphorus concentration of treated water cannot be suppressed. On the other hand, if it is excessive, in addition to the problem of cost, phosphorus necessary for the activated sludge in the aeration tank will be insufficient, and healthy activated sludge will not grow, which will hinder wastewater treatment.

  In addition, since the wastewater that flows into the first settling tank has a high organic matter concentration, the organic matter inhibits the reaction between the metal and phosphorus, so the amount of metal salt added is higher than when added in the aeration tank or the final settling tank. There is also a problem.

  As described above. The method of fixing phosphorus in activated sludge and suppressing the increase in the concentration of phosphorus in treated water is not suitable for the biological treatment method of organic wastewater having a step of solubilizing sludge as described above. is there. As described above, 2. In this method, the phosphorus in the sewage is fixed as a metal salt and settled and separated in the initial sedimentation tank. In addition to the increase in the amount of metal salt added, it is difficult to accurately determine the concentration (amount) of phosphorus. It is not practical to apply it to actual sewage whose concentration varies.

  As a result of diligent study on the above-described problems, the present inventors have solubilized sludge in a solubilization treatment step for solubilizing a part or all of the excess sludge separated into solid and liquid in the final sedimentation tank. By adding a substance that adsorbs and / or insolubilizes phosphate ions to the sludge being treated or to the sludge after the solubilization treatment, the solubilized sludge is first returned to the settling tank as described above. The inventors have found that the problems can be solved at once, and have reached the present invention.

  By having comprised as mentioned above, according to the processing method of this invention, although it has the sludge solubilization process process, the improvement of the phosphorus density | concentration in treated water can be suppressed reliably. In the treatment method of the present invention, since a substance that adsorbs and / or insolubilizes phosphate ions is added to the sludge being solubilized or to the sludge after the solubilization treatment, the above-mentioned 1 . As in the case of this treatment method, the metal salt and phosphorus hydroxide fixed with phosphorus are not solubilized, so that the power required for the solubilization treatment or the required amount of chemicals does not increase significantly.

  Furthermore, since the method of the present invention is configured so that the solubilized sludge to which a substance that adsorbs and / or insolubilizes phosphate ions is added is first returned to the settling tank, the metal phosphate, etc., in which phosphorus is fixed with the above substance, Since it is contained in the first settling sludge that comes out of the first settling tank and removed outside the system, it is possible to prevent the introduction of a metal such as aluminum for fixing phosphorus into the aeration tank. As a result, the aforementioned 1. Inhibiting the activity of activated sludge microorganisms, which was a concern in this method, does not occur. Moreover, since a substance that adsorbs and / or insolubilizes phosphate ions is added to the solubilized sludge, even if there is an excess or deficiency in the substance to be added, sewage, etc., to be treated in the aeration tank The phosphorus content is not fixed and removed. There is no problem with this method.

  As described above, in the method of the present invention, a solubilized sludge added with a substance that adsorbs and / or insolubilizes phosphate ions is first returned to the settling tank, so that a metal phosphate salt in which phosphorus is fixed with the above substance, etc. Is included in the first settling sludge that is first discharged from the settling tank and removed from the system. In this case, a configuration as shown in FIG. 3 is also a preferred embodiment of the present invention. That is, in the form shown in FIG. 3, after the sediment from the first sedimentation tank is concentrated in the primary sedimentation tank, the concentrated sludge is introduced into an anaerobic digester and treated by an anaerobic digestion method (methane fermentation method). Then, the organic solid matter in the concentrated sludge is decomposed into methane gas, and the liquid component is first introduced into the settling tank together with the inflowing water as return water, and is processed in the aeration tank. Sludge is dehydrated with a dehydrator to make a dehydrated cake. By comprising in this way, more organic solid substance in raw | natural water can be biodegraded, the efficiency can be raised, and the quantity of dehydration cake can be reduced simultaneously.

  Examples of substances that adsorb and / or insolubilize phosphate ions used in the method of the present invention include the following. First, examples of the metal or metal salt that makes phosphate ion insoluble or hardly soluble include iron, aluminum, zinc, calcium, magnesium, and metal salts thereof. More specifically, iron sulfate, poly iron sulfate, aluminum chloride, poly aluminum chloride, aluminum sulfate, sodium aluminate, zinc chloride, calcium chloride, calcium hydroxide, magnesium sulfate, magnesium chloride, magnesium hydroxide and the like can be mentioned. .

  Examples of substances that adsorb and / or fix phosphate ions include zeolite, calcium apatite, hydrotalcite, and the like.

Any conventionally known method can be used as the solubilization method in the solubilization process of excess sludge constituting the method of the present invention. Examples of sludge solubilization methods include the following methods.
(1) Solubilization by OH radical oxidation with iron salt and hydrogen peroxide (2) Solubilization by ozone oxidation (3) Solubilization by physical destruction by ultrasonic waves (4) Possible by mechanical grinding / destruction by bead mill etc. Solubilization (5) Solubilization by oxidation with chlorine (6) Solubilization by alkali (7) Solubilization by acid (8) Solubilization by heating to 50-90 ° C (9) Solubilization under high temperature and high pressure

  The present invention will be specifically described with reference to examples and comparative examples. The present invention is not limited by these examples. Hereinafter, “%” is based on mass unless otherwise specified.

Example 1
In this example, the bench plant experiment shown in FIG. 1 was performed. As an outline of the treatment flow, a part of the excess sludge is solubilized, and the remaining excess sludge is dehydrated together with the primary sedimentation sludge, and a substance that adsorbs and / or insolubilizes phosphate ions is added to the solubilized sludge. did.

  Specifically, the treatment was as follows. Sewage was used as the wastewater to be treated, and a treatment amount of 500 L / day was treated uniformly and continuously for 24 hours. As shown in FIG. 4, the wastewater is first separated and separated from the SS in a first sedimentation tank having a capacity of 100 L, and then activated sludge treatment is performed in an aeration tank having a capacity of 250 L, and activated in a final sedimentation tank having a capacity of 200 L. Sludge and treated water were separated into solid and liquid. The treated water that had been separated into solid and liquid was discharged, and the activated sludge that had settled was returned to the aeration tank at 150 L / day as return sludge. 5.25 L / day corresponding to 3.5% of the amount of returned sludge was branched from the returned sludge and sent to a solubilizing apparatus having a volume of 2 L for solubilization.

  In this example, polyaluminum chloride (PAC) was continuously added at 1 g / day in terms of aluminum atoms to the sludge after the solubilization treatment, and then mixed with the influent wastewater and returned to the initial sedimentation tank. The excess sludge was appropriately extracted so that the MLSS of the aeration tank was maintained at 1,800 mg / l. The sludge solubilization treatment in the solubilization treatment apparatus was carried out by adjusting the pH to 3 with sulfuric acid and adding 5% of hydrogen peroxide to the dry matter equivalent of the treated sludge.

(Example 2)
In the bench plant shown in FIG. 2 having the same scale as that used in the processing of Example 1, the same sewage as in Example 1 is used as raw water, and specifically, organic wastewater is processed as shown in FIG. It was. In this example, the amount of sludge to be sent to the solubilization apparatus was 7.5 L corresponding to 5% of the amount of returned sludge. In addition, in order to maintain the MLSS of the aeration tank at 1,800 mg / l, the amount of sludge sent to the solubilization treatment apparatus was changed to adjust the MLSS to 1,800 mg / l, and no excess sludge was discharged. . Except for the above, wastewater treatment was performed under the same conditions as in the treatment method of Example 1. The PAC added to the solubilized sludge was also 1 g / day as in Example 1.

(Comparative Example 1)
In this comparative example, as shown in FIG. 6, the same sewage as in the example was treated as raw water. Specifically, all the other conditions including the amount of PAC addition and the solubilization treatment conditions were performed in Example 2 except that the conditions of Example 2 were changed to the entrance of the final precipitation tank only at the PAC addition position. Wastewater treatment was carried out in the same manner as described above.

(Comparative Example 2)
In this comparative example, as shown in FIG. 7, the same sewage as in the example was treated as raw water. Specifically, the solubilization processing apparatus was removed from the treatment system of Comparative Example 1, and the other treatment conditions were the same as those in Comparative Example 1, and the wastewater treatment was performed.

(Processing result by processing of Examples 1 and 2 and Comparative Examples 1 and 2)
The treatment methods of Example 1, Example 2, Comparative Example 1 and Comparative Example 2 performed above were simultaneously operated for 3 months. And the average water quality for the latter two months and the daily average amount of dehydrated cake (in terms of dry sludge amount) were measured, and the results are summarized in Table 1.

  As shown in Table 1, the quality of the treated water was 2 mg / l or less for both SS and BOD in both the examples and the comparative examples, and the total phosphorus was 1 mg / l or less, and good results were obtained. Obtained. Moreover, there was no big difference about the total nitrogen of treated water, and it was 11-15 mg / l. The amount of dehydrated cake generated (dry sludge base) is 69 g / day in the case of the treatment method of Example 2, which is the least generated amount and the most generated amount, without the sludge solubilization process. Compared to 92 g / day in the case of the processing method of Example 2, the reduction was 25%. Similarly, in the case of the processing method of Example 1, it was 75 g / day, which was 18.5% lower than that of the processing method of Comparative Example 2.

  In the case of the treatment method of Comparative Example 1, the amount of sludge solubilized was the same as in the case of the treatment method of Example 2, but the amount of dehydrated cake generated was 74 g / day, which was higher than that in Example 2, and allowed. It became substantially the same value as Example 1 with little amount of solubilized sludge. Although this cause is not certain, since the aluminum content in MLSS shown in Table 1 differs, it is guessed that the aluminum content may have influenced. That is, the present inventors presume that the aluminum contained in the sludge during the solubilization process may have affected the reaction of the solubilizer. In any of the processing conditions of the example and the comparative example, the aluminum addition amount was the same, whereas the aluminum concentration in MLSS was in MLSS in the case of the processing of Example 1 and Example 2. The aluminum content was as low as 0.1%. On the other hand, for example, in the case of the treatment of Comparative Example 1, it was found that the aluminum content in MLSS was 1.4%, indicating a concentration 14 times that of Example 1. Further, even in the method of Comparative Example 2 in which the PAC was added by the introduction route to the final sedimentation tank without providing the sludge solubilization step, the aluminum content in MLSS showed a concentration 17 times that of the Example, In addition, there was concern about inhibiting the activity of activated sludge microorganisms in the aeration tank. From these, the usefulness of adding a substance that adsorbs and / or insolubilizes phosphate ions such as PAC to the solubilized sludge is confirmed in the embodiment of the present invention. It was.

(Example 3)
In this example, the treatment method of the present invention was applied to an actual sewage treatment facility, and the effect was confirmed. Specifically, in the configuration of the treatment tank shown in FIG. 8, the treatment was performed without discharging the excess sludge as in Example 2. This treatment facility had a planned influent water volume of 7,000 m ³ / day, and an average inflow water quantity of 5,600 m ³ / day during a period of three months when the treatment method of the present invention was applied. As shown in FIG. 8, the waste water is first separated by sedimentation the SS component in the first precipitation tank of capacity 500 meters ^3, it was subjected to activated sludge treatment in the aeration tank volume 2,500 m ^3. This aeration tank was divided into four tanks in series and operated by an anaerobic aerobic method. In the final sedimentation tank with a capacity of 1,500 m ³ , the activated sludge and the treated water were solid-liquid separated, the treated water was discharged, and the precipitated activated sludge was returned to the aeration tank with an average flow rate of 195 m ³ / day.

10 m ³ / day corresponding to about 5.1% of the amount of returned sludge was branched from the returned sludge and sent to a solubilizing apparatus to be solubilized. After 12 kg / day of sodium aluminate was continuously added to the solubilized sludge in terms of aluminum atoms, it was mixed with the influent wastewater and returned to the first sedimentation tank. The MLSS of the aeration tank was maintained at 1,800-2,200 mg / l. When MLSS was lowered, the amount of treated sludge in the solubilization treatment apparatus was increased, and when it was raised, adjustment was made by reducing the amount of treated sludge, and excess sludge was not discharged. In the solubilizer, the pH was adjusted to 10 with caustic soda, and 1% of an oxygen acid oxidizer was added to the dry matter equivalent of the treated sludge to solubilize the sludge. The first settling sludge discharged from the first settling tank is dewatered after gravity concentration. Table 2 shows the average water quality after one month of treatment carried out in this example and the daily average amount of dehydrated cake (in terms of dry sludge amount).

(Comparative Example 3)
In Table 2, as Comparative Example 3, the water quality analysis results for the previous year in which the application test of this example was performed at the same sewage treatment plant, the sludge generation amount, and the aluminum concentration in MLSS are shown. In Comparative Example 3, as a countermeasure against phosphorus in the treated water, PAC was continuously injected into the inflow portion of the final sedimentation tank at 2 to 3 mg / l in terms of aluminum atoms.

  As shown in Table 2, in both the methods of Example 3 and Comparative Example 3, the quality of the treated water was SS and BOD of 2 mg / l or less, and the total phosphorus was 1 mg / l or less. Also good results. The total nitrogen was 3.2 mg / l for the method of Example 3 and 3.5 mg / l for the method of Comparative Example 3, both of which were good results. In contrast, the amount of dehydrated cake generated (dry sludge base) was 690 kg / day for the method of Example 3, whereas it was 885 kg / day for the method of Comparative Example 3. The amount of dehydrated cake of No. 3 was less than 20%, and a sludge reduction effect was also observed. The aluminum concentration in MLSS was 0.2% in the case of the method of Example 3, whereas it was 1.5% in the case of the method of Comparative Example 3, which was the case of the method of Example 3. Was confirmed to be a low concentration.

Claims (4)

Even without low, the first precipitation tank, and bioreactor tank, in activated sludge treatment method for processing organic waste water with the final sedimentation tank, the phosphate ions to the inlet of bioreactor tank or final settling tank Excess sludge separated and liquid-separated in the final settling tank without adding a substance that adsorbs and / or insolubilizes, and without adding a substance that adsorbs and / or insolubilizes phosphate ions to the inlet of the initial settling tank . A solubilization treatment step for solubilizing a part or all of the solution is provided, and in the solubilization treatment step, phosphate ions are added to the sludge being solubilized or to the sludge after the solubilization treatment. After the addition of material that adsorbs and / or insolubilized, to return to the first precipitation tank without solid-liquid separation of sludge solubilized, the material fixing the phosphorus is included in primary sludge exiting the first sedimentation tank Removed from the system Biological treatment method of organic wastewater, characterized in that the sea urchin configuration.   The biological treatment method for organic wastewater according to claim 1, wherein the organic wastewater is sewage.   The biological treatment of organic wastewater according to claim 1 or 2, wherein the substance that adsorbs and / or insolubilizes the phosphate ions is a metal or metal salt that binds to phosphate ions to form an insoluble or hardly soluble salt. Method.   The biological treatment method for organic wastewater according to claim 1 or 2, wherein the substance that adsorbs and / or insolubilizes the phosphate ions is selected from the group consisting of aluminum or iron and salts thereof.

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