JP2008207066A - Treatment method of organic wastewater - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a novel treatment method of organic wastewater capable of markedly reducing the occurrence amount of excess sludge produced by accompanying the biological treatment of the organic wastewater and reducing the effect on the treatment liquid properties of the organic wastewater. <P>SOLUTION: In the treatment method of the organic wastewater wherein the biologically treated mixture, which is obtained after the organic wastewater is biologically treated in a biological treatment tank, is separated into treated water and sludge by a solid-liquid separation method and a part or the whole of the sludge is subjected to solubilizing treatment for solubilizing the organic matter in the sludge to return the treated sludge to the biological treatment tank, at least a kind of a compound selected from sulfuric acid, carbonic acid, hydrogen carbonate and salts of them is added so as to reach a range of 1-30 mmol/L with respect to the amount of raw water on the basis of sulfuric ions, carbonate ions or hydrogen carbonate ions. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for biologically treating organic wastewater, and more specifically, organic wastewater capable of incorporating sludge solubilization into the biological treatment of the organic wastewater to reduce the amount of generated excess sludge. It relates to the processing method.

  Conventionally, surplus sludge generated by biological treatment such as the activated sludge method has been disposed of by sludge treatment such as dehydration, drying, and incineration, but the biggest problem is that the disposal requires significant expenses and equipment costs. ing. The amount of excess sludge generated by the conventional activated sludge method is generally 0.6 to 0.8 kg · ss (sludge) per 1 kg of BOD to be removed, and it is well known that a very large amount of excess sludge is generated. Moreover, since the excess sludge is qualitatively difficult to dehydrate, its disposal becomes increasingly difficult.

As a method for reducing the generation amount of excess sludge, many methods for solubilizing excess sludge and returning them to a biological treatment tank (aeration tank) have been proposed. For example, surplus sludge is solubilized by treating with alkali and returned to the biological treatment tank (see Patent Document 1), surplus sludge is destroyed by ultrasonic, homogenizer, mixer, or rapid pressure fluctuation, or oxidized by ozone gas A method of solubilizing and returning to a biological treatment tank by decomposing has been proposed (see Patent Document 2).
On the other hand, as a method of reducing the generation of surplus sludge, a solubilization means for solubilizing a part or all of the surplus sludge is provided in the organic wastewater treatment process, and the solubilization is treated with an alkaline agent by using a homogenizer, a mixer or the like. A method of combining processing is also known (see Patent Document 3).
In these treatments, the method of solubilizing excess sludge and treating it in a biological treatment tank is advantageous when a high solubilization rate is obtained in a shorter time and with lower energy when sludge is re-substrateed. There has been a demand for a method that can solubilize sludge more efficiently.
Japanese Patent Publication No.49-11813 Japanese Patent Publication No.57-19719 JP 2002-113487 A

  The present invention is a novel organic wastewater treatment method that can remarkably reduce the amount of surplus sludge generated during biological treatment of organic wastewater and that has little effect on the treatment liquid properties of organic wastewater. The purpose is to provide.

  As a result of earnest research in view of such circumstances, the present inventor performed solubilization treatment of solid-liquid separated sludge in the presence of a specific amount of sulfuric acid, carbonic acid, hydrogen carbonate or a salt thereof, The present inventors have found that the sludge solubilization rate is improved and the amount of surplus sludge generated can be significantly reduced.

  That is, in the present invention, after biologically treating organic wastewater in a biological treatment tank, the biological treatment mixture is solid-liquid separated into treated water and sludge, and the organic matter in the sludge is partially or wholly contained. In the method for treating organic wastewater to be solubilized and then returned to the biological treatment tank, one type selected from sulfuric acid, carbonic acid, hydrogen carbonate and salts thereof in the system in which sludge circulates An organic wastewater treatment method is provided, wherein two or more kinds are added so as to be in a range of 1 mmol / L to 30 mmol / L with respect to the amount of raw water on the basis of sulfate ion, carbonate ion or bicarbonate ion. To do.

  According to the organic wastewater treatment method of the present invention, surplus sludge generated with biological treatment of organic wastewater can be effectively solubilized, thereby significantly reducing the amount of surplus sludge generated with less input energy. Can be made.

The organic wastewater treatment method of the present invention can be applied to biological treatment of various organic wastewaters that generate excess sludge. This biological treatment may be an aerobic biological treatment or an anaerobic biological treatment.
Examples of the aerobic biological treatment include an activated sludge method and a biofilm method. The activated sludge process is an aerobic biological treatment of organic wastewater in the presence of activated sludge. Organic wastewater is mixed with activated sludge in an aeration tank and aerated, and the mixture is concentrated with a concentrator. A standard activated sludge method is generally used in which a part of the concentrated sludge is returned to the aeration tank. However, a modified treatment method may be used. The biofilm method is a treatment method in which a biofilm is formed on a carrier and brought into contact with organic waste water under aerobic conditions.
Examples of the anaerobic biological treatment include a so-called anaerobic digestion method and a high-load anaerobic treatment method.
Among the biological treatments of the above various organic wastewaters, it can be suitably applied to the activated sludge method that is frequently used for the treatment of organic wastewaters. Hereinafter, the present invention will be described in detail with reference to the accompanying drawings, taking the activated sludge method as an example.

  A general flow of a conventional standard activated sludge process system is as shown in FIG. In the flow of the treatment system of FIG. 1, organic waste water is supplied from the line 1 to the aeration tank 2, aerated in the aeration tank 2, subjected to aerobic biological treatment with activated sludge, and then through the line 3 to the sludge settling tank 4 Sent to. After the solid-liquid separation, the supernatant liquid of the sludge settling tank 4 is discharged and discharged from the line 5 as treated water, while the precipitated sludge in the sludge settling tank 4 is returned to the aeration tank 2 via the line 6 as return sludge. A part of this returned sludge is collected and passed through the line 7 as surplus sludge and supplied to the sludge concentration process 8 as necessary to further increase the solids concentration, and then passed through the line 9 to the sludge dewatering process 10. The dehydrated excess sludge 11 that is guided and dehydrated is discharged out of the system.

FIG. 2 shows the flow of the treatment system in which the conventional standard activated sludge method as described above is subjected to the solubilization treatment and then returned to the biological treatment tank. The present invention will be described with reference to FIG.
In the flow of the treatment system of the embodiment of the present invention shown in FIG. 2, organic waste water is supplied from the line 1 to the aeration tank 2, aerated in the aeration tank 2, and subjected to aerobic biological treatment with activated sludge, and then the line 3 is sent to the sludge settling tank 4. After the solid-liquid separation, the supernatant liquid of the sludge settling tank 4 is discharged and discharged from the line 5 as treated water, while the precipitated sludge in the sludge settling tank 4 is returned to the aeration tank 2 via the line 6 as return sludge. And after a part of said return sludge is fractionated, it passes through the line 7 as surplus sludge, and is supplied to the sludge concentration process 8 as needed, and solid concentration is concentrated to about 0.5 to 5 weight%. A part of the excess sludge is guided to the sludge dewatering step 10 via the line 9 and dehydrated, and the obtained dehydrated surplus sludge 11 is discharged out of the system. The flow up to this point is the same as the flow of the conventional standard activated sludge process.
A part of the returned sludge or a part or all of the sludge concentrated in the concentration tank is led to the sludge solubilization tank 13 via the line 12 and solubilized, and the solubilized product is passed through the line 14 to the aeration tank. 2 and biologically treated with activated sludge. However, when the solid concentration of the excess sludge separated from the returned sludge is high, it is not necessary to provide the sludge concentration step 8 to concentrate the excess sludge.
Moreover, the surplus sludge discharged | emitted out of the system is eliminated by solubilizing the sedimentation sludge about 2 to 3.5 times the surplus sludge generation amount in the condition where this treatment system is not solubilized. You can also.

  In the present invention, conventionally used aeration tank 2 and sludge settling tank 4 can be appropriately used. Further, as the concentration means in the sludge concentration step 8, conventionally used concentration means such as gravity sedimentation separators, flotation separators, centrifuges, membrane separators, screw dehydrators and the like can be defined and used. Further, as the dewatering means of the sludge dewatering step 10, conventionally used dewatering means such as a centrifugal separator, a belt filter dehydrator, a screw press dehydrator and the like can be appropriately used.

  In the present invention, the addition position of sulfuric acid, carbonic acid, hydrogen carbonate or a salt thereof added to promote solubilization of organic substances is not particularly limited as long as it is in a system in which sludge circulates. Here, the system in which the sludge circulates means the system in which the sludge circulates, including a biological treatment tank (aeration tank) and a solid-liquid separation tank. For example, the line 1, the aeration tank 2, the line 3, the line 6, the line 12, the sludge solubilization tank 13, the line 14 and the like shown in FIG. 2 are listed, and the sludge is fed from the sludge concentration process to the sludge solubilization tank. Line 7 and sludge concentration process 8 etc. are mentioned. Among these, from the viewpoint of improving the solubilization rate, the positions of the line 1, the aeration tank 2, the line 3, the line 12, the line 7, and the sludge concentration process 8 are preferable, and the line 1, the line 12, and the sludge concentration process 8 are particularly preferable. .

  The form of sulfuric acid, carbonic acid, hydrogen carbonate or a salt thereof is not particularly limited, but it is preferable to use a form that dissolves when added. Examples of the salt include alkali metal salts such as sodium and potassium. Among these, a preferable form is an alkali metal salt, and sodium sulfate, sodium carbonate, and sodium hydrogen carbonate, which are sodium salts, are particularly preferable. These may be used alone or in combination of two or more.

  From the viewpoint of improving the solubilization rate, the amount of sulfuric acid, carbonic acid, hydrogen carbonate or a salt thereof added ranges from 1 mmol / L to 30 mmol / L with respect to the amount of raw water on the basis of sulfate ion, carbonate ion or hydrogen carbonate ion. Particularly preferred is 1.5 mmol / L to 25 mmol. When using 2 or more types of sulfuric acid, carbonic acid, hydrogen carbonate, or their salts, it should just add so that it may become the said addition amount as a whole quantity. In addition, when sulfate, carbonate, hydrogen carbonate, or the like is contained in the raw water, the total amount may be adjusted and added so that the total amount falls within the range of the addition amount.

The solubilization treatment method in the sludge solubilization tank 13 is not limited, but a solubilization treatment method combining solubilization using an alkali agent, solubilization by physical crushing, and alkali agent and physical crushing is particularly suitable. is there.
Although it does not specifically limit as an alkaline agent, For example, sodium hydroxide, sodium carbonate, sodium hydrogencarbonate etc. are mentioned, Especially sodium hydroxide is preferable. Although the addition amount of an alkali agent is not specifically limited, 0.005-0.1N should just be sufficient with respect to the excess sludge to solubilize, Preferably it is 0.01-0.05N.
Examples of physical crushing include crushing by a mixer, a mill, and an ultrasonic wave, and a mixer and a mill are particularly preferable.

The time for the solubilization treatment is not particularly limited, but is preferably 1 minute to 300 minutes, particularly preferably 3 minutes to 250 minutes, and more preferably 10 minutes to 200 minutes.
The sludge solubilizing solution after the solubilization treatment (hereinafter referred to as “solubilizing solution”) may be subjected to neutralization treatment or decolorization treatment with an oxidizing agent as necessary. By performing the decolorization treatment, it is possible to reduce the adverse effect on the color of the solubilized treatment product generated when the volume of excess sludge is reduced and the hue of the treated water resulting therefrom. Although the decoloring treatment and the neutralization treatment can be used in combination, it is preferable to perform the decoloring treatment before the neutralization treatment. For the neutralization treatment, a mineral acid such as sulfuric acid, a spent waste acid or the like can be used. The oxidizing agent is preferably hydrogen peroxide, sodium peroxide, sodium percarbonate, etc., which have strong oxidizing power and change itself to be harmless to activated sludge after decomposition, and hydrogen peroxide is particularly preferable.
In the case of the same solubilization amount, it is possible to increase the reduction rate of the excess sludge generation amount by increasing the solubilization rate.

  The method for treating organic waste water of the present invention is particularly useful for raw water in which the calcium ion concentration in raw water to be treated in activated sludge is in the range of 10 ppm to 200 ppm, preferably in the range of 20 ppm to 100 ppm.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the technical scope of the present invention is not limited to these examples.

Example 1
Factory wastewater (COD = 80-120mg / L (test period average 100mg / L), Ca concentration 30ppm-50ppm (test period average 40ppm)) aeration time 12 hours, activated sludge MLSS = 3000mg / L 40L aeration tank (COD After supplying to a volume load of 0.20 (kgCOD / m3 · day), the activated sludge was settled and separated in a 20 L settling tank to obtain a precipitated sludge having a solid concentration of 0.5 to 1% by weight. The sulfate ion concentration of the raw water was 0.3 mmol / L, the bicarbonate ion concentration was 0.1 mmol / L, and the carbonate ion concentration was 0.1 mmol / L. The amount of trivalent metal in the raw water was 1 ppm or less.
In this wastewater treatment, sodium sulfate was added to the inlet of the precipitation tank so that the sulfate ion concentration was 2 mmol / L with respect to the amount of raw water.
In the above factory wastewater treatment amount, the factory wastewater treatment amount is set to 0.08 m ³ / day, 1.2 to 2.4 L / day (dry-base 12.0 g / day) of the precipitated sludge is extracted, and the remaining precipitated sludge is returned to the aeration tank. did. Next, this extracted sludge is introduced into a batch-type sludge solubilization tank, and set to a rotation speed of 8,000 rpm with an in-line mixer (a pipeline homomixer made by Special Machine), and caustic soda is added. It was added to 0.025N and treated for 10 minutes to solubilize sludge. The solubilized solution was added to the aeration tank at a constant rate to perform aerobic biological treatment. As a result of continuing the operation according to the above conditions for 30 days, the average solubilization rate was 38%. Furthermore, the total surplus amount of sludge extracted so that the MLSS of the activated sludge tank was kept constant during that period was 22 g (dry weight).

Example 2
In Example 1, the operation was performed in the same manner except that sodium sulfate was added so as to have a sulfate ion concentration of 20 mmol / L with respect to the amount of raw water. As a result of continuing the operation according to the above conditions for 30 days, the average solubilization rate was 44%. Furthermore, the total amount of excess sludge extracted during this period so that the MLSS in the activated sludge tank was kept constant was 10 g (dry weight).

Comparative Example 1
In Example 1, the operation was performed in the same manner except that the operation was performed without adding sodium sulfate. As a result of continuing the operation according to the above conditions for 30 days, the average solubilization rate was 20%. Furthermore, the total amount of excess sludge extracted so that the MLSS of the activated sludge tank was kept constant during that period was 68 g (dry weight).

Example 3
In Example 1, the operation was performed in the same manner except that the operation was performed by changing the addition position of sodium sulfate to the entrance of the concentration tank. As a result of continuing the operation according to the above conditions for 30 days, the average solubilization rate was 37%. Furthermore, the total surplus amount of sludge extracted so that the MLSS in the activated sludge tank was kept constant during that period was 30 g (dry weight).

Example 4
In Example 3, the operation was performed in the same manner except that sodium bicarbonate was added instead of sodium sulfate. As a result of continuing the operation according to the above conditions for 30 days, the average solubilization rate was 33%. Further, during this period, the total amount of excess sludge extracted from the activated sludge tank so as to be constant was 35 g (dry weight).

Example 5
In Example 3, the operation was performed in the same manner except that sodium carbonate was added instead of sodium sulfate. As a result of continuing the operation according to the above conditions for 30 days, the average solubilization rate was 35%. Furthermore, the total surplus amount of sludge extracted so that the MLSS in the activated sludge tank was kept constant during that period was 30 g (dry weight).

Example 6
In Example 2, the operation of the solubilization process was changed to an in-line mill (IKA Lab Pilot 2000/4) instead of the in-line mixer, except that the rotation speed was set to 6,000 rpm and the process was performed for 10 minutes in the same manner. Drove. As a result of continuing the operation according to the above conditions for 30 days, the average solubilization rate was 42%. Furthermore, the total amount of excess sludge extracted during this period so that the MLSS in the activated sludge tank was kept constant was 10 g (dry weight).

Example 7
In Example 2, the operation was performed in the same manner except that the solubilization treatment was carried out for 10 minutes with ultrasonic waves (ultrasonic wave generator, output 100 W) instead of the in-line mixer. As a result of continuing the operation according to the above conditions for 30 days, the average solubilization rate was 48%. Furthermore, the total excess sludge amount extracted so that the MLSS of the activated sludge tank was kept constant during that period was 4 g (dry weight).

Example 8
In Example 2, the operation of the solubilization treatment was performed in the same manner except that the treatment was carried out for 10 minutes without adding caustic soda with ultrasonic waves (ultrasonic wave generator, output 100 W) instead of the in-line mixer. . As a result of continuing the operation according to the above conditions for 30 days, the average solubilization rate was 38%. Further, during this period, the total amount of excess sludge extracted from the activated sludge tank so as to be constant was 35 g (dry weight).

Comparative Example 2
In Example 8, the operation was performed in the same manner except that the operation was performed without adding sodium sulfate. As a result of continuing the operation according to the above conditions for 30 days, the average solubilization rate was 14%. Furthermore, the total surplus amount of sludge extracted so that the MLSS of the activated sludge tank was kept constant during that period was 90 g (dry weight).

  The table below summarizes the above examples and comparative examples.

It is a general flow sheet of a conventional standard activated sludge process system. It is a flow sheet of a processing system of an example of an embodiment of the present invention.

Claims (4)

  After biological treatment of organic wastewater in a biological treatment tank, the biological treatment mixture is solid-liquid separated into treated water and sludge, and solubilization treatment is performed to solubilize organic matter in part or all of the sludge. In the method for treating organic wastewater that is returned to the biological treatment tank, one or more selected from sulfuric acid, carbonic acid, hydrogen carbonate, and salts thereof are added to sulfuric acid in the system in which sludge circulates. An organic wastewater treatment method comprising adding 1 to 30 mmol / L with respect to the amount of raw water on the basis of ions, carbonate ions or hydrogen carbonate ions.   The treatment method according to claim 1, wherein the salt of sulfuric acid, carbonic acid or hydrogen carbonate is a sodium salt.   The method for treating organic waste water according to claim 1 or 2, wherein the solubilization treatment for solubilizing organic matter in the sludge is treatment by addition of alkali or treatment by mechanical crushing.   The organic wastewater treatment method according to any one of claims 1 to 3, wherein the organic wastewater contains 10 ppm to 200 ppm of calcium ions.

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