JP4066458B2 - Method and apparatus for reducing excess sludge volume - Google Patents

Description

  The present invention relates to a method and an apparatus for volume reduction of surplus sludge, and in particular, surplus sludge is reduced by solubilizing surplus sludge generated when organic wastewater is biologically treated in a biological treatment tank and returning it to the biological treatment tank. The present invention relates to a method for reducing the volume of excess sludge.

  As an organic wastewater purification method, there is an activated sludge method for biologically purifying organic wastewater by bringing the organic wastewater into contact with activated sludge containing aerobic microorganisms in a biological treatment tank under aerobic conditions. Widely adopted. In this activated sludge method, after organic wastewater is biologically treated in a biological treatment tank, the activated sludge accompanying the treated water is solid-liquid separated and returned to the biological treatment tank as return sludge. Because it decomposes pollutants in organic wastewater and self-propagates as a nutrient source, in order to maintain a constant amount of activated sludge in the biological treatment tank, it is necessary to periodically extract the self-propagated sludge from the biological treatment tank . The extracted excess sludge is dewatered and then incinerated or directly landfilled. However, not only the problem of dioxin generation due to incineration, but also the problem of an increase in the processing cost for incineration and landfilling has become a problem, and there is an increasing need to reduce excess sludge.

  As a method for reducing the volume of excess sludge, a method has been developed in which the excess sludge is solubilized and easily decomposed by microorganisms and then returned to the biological treatment tank to reduce the amount of sludge generated. As a solubilization method, there is a method of mechanically, physically or chemically destroying the cell wall of a microorganism which is a main component constituting sludge. Mechanical and physical solubilization includes a crushing process using a wet mill, a disk, and ultrasonic waves, and chemical solubilization includes oxidation processes such as ozone and Fenton reaction. In addition, there is a biological treatment using enzymes of thermophilic bacteria. Among these methods, the ozone method is widely adopted as it can stably reduce excess sludge.

However, the method of using ozone has many disadvantages such as a waste ozone treatment device and the like, an expensive ozone generator, ozone being harmful to the human body, and a lot of treated sludge foaming. Therefore, Patent Document 1 introduces chlorine dioxide as a solubilizer that oxidizes excess sludge and solubilizes it in the same manner as ozone. This chlorine dioxide has a strong oxidizing power and is widely used as a bleaching agent and disinfectant. By using this as a solubilizing agent, there is not much foaming of the treated sludge, and a removal device such as the ozone method is used. There is an advantage that the apparatus is relatively inexpensive. In Patent Document 2, alkali is introduced as a chemical used in the chemical solubilization method of excess sludge.
Japanese Patent Laid-Open No. 11-147801 Japanese Examined Patent Publication No. 6-61550

  However, when chlorine dioxide is used as a solubilizing agent, if the chlorine dioxide is excessively injected, the quality of treated water may be deteriorated. Since chlorine dioxide is acidic, the pH of the solubilized sludge is 2-3. Since the activated sludge is deactivated when it is returned to the biological treatment tank as it is, the neutralization treatment must be performed after the solubilization treatment. There is a problem in that the running cost of the hydrating agent increases.

  The present invention has been made in view of such circumstances, and the object of the present invention is to efficiently reduce excess sludge so as not to deteriorate the quality of treated water, and after solubilization treatment. It is an object of the present invention to provide a surplus sludge solubilization method and apparatus that are economically superior because it is not necessary to use a neutralizing agent that neutralizes the excess sludge.

  The inventor injects chlorine dioxide at an injection amount of 0.01 to 0.02 g per 1 g of dry base of surplus sludge as a solution that adversely affects activated sludge in the biological treatment tank by excessive injection of chlorine dioxide, Acquire the knowledge that it is possible to eliminate the excess and deficiency of the injection amount of chlorine dioxide, satisfy both the volume reduction rate of surplus sludge and the quality of treated water, and control the injection amount range with the oxidation-reduction potential. And obtained knowledge that it can be controlled easily and accurately.

For a first aspect of the present invention to achieve the object, reducing the excess sludge by the excess sludge produced during the biological treatment of organic wastewater in the biological treatment tank solubilized back into the biological treatment tank in volume reduction method of surplus sludge iodide, a step of distributing the excess sludge to the solubilizer into two, a step of solubilizing excess sludge whereas the said dispensing with chlorine dioxide, other excess that the distribution A step of solubilizing sludge with an alkaline liquid, a step of mixing and neutralizing the acidic surplus sludge solubilized with chlorine dioxide and the alkaline surplus sludge solubilized with the alkaline liquid, and then returning to the biological treatment tank ; A step of measuring the pH of the mixed surplus sludge, and based on the measurement result, a distribution ratio of the surplus sludge before solubilization so that the pH of the mixed surplus sludge falls within a predetermined range. Change Characterized by comprising a and.

According to claim 1 , the surplus sludge to be solubilized is distributed into two, and one of the distributed surplus sludge is solubilized with chlorine dioxide. Thereby, the excess sludge solubilized with chlorine dioxide becomes acidic. On the other hand, the other excess sludge distributed is solubilized with alkali. Thereby, the excess sludge solubilized with alkali becomes alkaline. And it was made to return to a biological treatment tank, after mixing acidic surplus sludge and alkaline surplus sludge. In this way, neutralization necessary to return the excess sludge to the biological treatment tank can be performed by mixing the acidic excess sludge and the alkaline excess sludge, so that the acidic excess sludge is neutralized. Neither the neutralizer nor the neutralizer for neutralizing the excess alkaline sludge is required. Thereby, surplus sludge can be solubilized economically. Distributing into two in Claim 1 does not mean dividing equally, but when the excess sludge solubilized with chlorine dioxide and the excess sludge solubilized with alkali are mixed, the pH is neutral (pH 6. What is necessary is just to distribute so that it may fall in the range of 5-7.5).

In order to achieve the above object, Claim 2 of the present invention reduces the excess sludge by solubilizing excess sludge generated when biological wastewater is biologically treated in a biological treatment tank and returning it to the biological treatment tank. In an apparatus for reducing the volume of excess sludge to be contained, a distribution means for distributing the solubilized excess sludge into two, a first solubilization treatment tank for solubilizing one of the distributed excess sludge with chlorine dioxide, The second solubilization treatment tank for solubilizing the other surplus sludge distributed with an alkali solution, the mixing tank for mixing the excess sludge solubilized in the first and second solubilization treatment tanks, and the mixing A return line for returning the mixed surplus sludge mixed in the tank to the biological treatment tank, and pH measuring means for measuring the pH of the mixed surplus sludge, and the distributing means is measured by the pH measuring means. The pH of the mixed surplus sludge Characterized in that it is configured the distribution ratio of the previous excess sludge the solubilizer so as to enclose to the variable.

Claim 2 constitutes the method of claim 1 as an apparatus.

  As described above, according to the surplus sludge solubilization method and apparatus of the present invention, excess and deficiency of the amount of chlorine dioxide injected into the excess sludge can be eliminated, so that the excess quality of the treated water is not deteriorated. The sludge can be efficiently reduced in volume, and the use of a neutralizing agent that neutralizes the excess sludge after the solubilization treatment is not necessary, which is economically superior.

  The preferred embodiments of the method and apparatus for reducing excess sludge according to the present invention will be described in detail below with reference to the accompanying drawings.

  FIG. 1 is an overall configuration diagram of a wastewater treatment system incorporating the first embodiment of the excess sludge volume reducing device of the present invention.

  The wastewater treatment system 10 mainly includes a biological treatment device 12 that biologically treats organic wastewater with activated sludge and a volume reduction device 14 that reduces excess sludge generated in the biological treatment device 12. The

  The biological treatment apparatus 12 is mainly composed of a biological treatment tank 16 in which activated sludge having aerobic microorganisms floats, and a solid-liquid separation tank 18 for solid-liquid separation of treated water from the biological treatment tank 16 and activated sludge. The

  An aeration pipe 20 is provided at the bottom of the biological treatment tank 16, and the aeration pipe 20 is connected to the blower 24 via an air pipe 22. Thereby, in the biological treatment tank 16, the organic waste water and activated sludge which flow into the biological treatment tank 16 from the raw water pipe 26 by the raw water pump 28 come into contact with each other under aerobic conditions, and the biological treatment is performed and the organic treatment is performed. Waste water is purified. The purified treated water is sent to the solid-liquid separation tank 18 through the water flow pipe 30 and the activated sludge flowing out from the biological treatment tank 16 along with the treated water is subjected to solid-liquid separation. The supernatant water separated from the solid-liquid separation tank 18 is discharged out of the system from the treated water pipe 17 as treated water. On the other hand, among the activated sludge separated in the solid-liquid separation tank 18, only the amount of sludge necessary for maintaining the activated sludge concentration for purifying the organic wastewater in the biological treatment tank 16 is the sludge return pump 32. Is returned to the biological treatment tank 16 through the sludge return pipe 33. Among them, 3 to 10 times the amount of excess sludge generated by biological treatment is sent to the volume reduction device 14 via the excess sludge pipe 35 by the sludge transfer pump 34. The excess sludge solubilized by the volume reduction device 14 is returned to the biological treatment tank 16 by the solubilized sludge return pump 31 via the solubilized sludge return pipe 39.

  The volume reduction device 14 mainly includes a solubilization treatment tank 36 with a stirrer 37 for solubilizing excess sludge with chlorine dioxide, and 0.01 to 0 chlorine dioxide per gram of dry sludge in the solubilization treatment tank 36. It is comprised with the automatic injection | pouring control mechanism 38 for inject | pouring in the range of 0.02g.

  In the automatic injection control mechanism 38, the sludge concentration of excess sludge is first measured over time by a sludge concentration meter 40 (MLSS meter) provided in the sludge return pipe 33. The measurement may be continuous measurement or intermittent measurement. The measurement value measured by the sludge concentration meter 40 is sent to the converter 42, and the converter 42 converts the amount of excess sludge in the solubilization tank 36 from the measured sludge concentration into a dry base. Thereby, the amount of dry sludge in the solubilization processing tank 36 can be obtained. Next, the converted value from the converter 42 is sent to the calculator 44, and the calculator 44 is based on the converted value, so that chlorine dioxide is injected in an amount of 0.01 to 0.02 g per 1 g of dry base of excess sludge. The amount of injection into the solubilization tank 36 required for the calculation is calculated. In this case, the solubilization processing in the solubilization processing tank 36 may be performed continuously, or an intermediate tank (not shown) may be provided in the excess sludge pipe 35 to perform batch processing. And the control means 46 controls the injection amount of the chlorine dioxide from the injection apparatus 48 based on this calculation result. In this case, gaseous chlorine dioxide can be used, but it is preferable to use chlorine dioxide water in which chlorine dioxide is dissolved in water. That is, the injection device 48 includes a storage tank 50 that stores chlorine dioxide water, an injection pipe 52 that extends from the storage tank 50 to the solubilization tank 36, and an automatic valve 54 that is provided in the injection pipe 52. Then, the control means 46 controls the injection amount of the chlorine dioxide water by adjusting the opening degree of the automatic valve 54. According to this apparatus configuration, the chlorine dioxide can be automatically controlled with high accuracy so that the amount of chlorine dioxide injected per 1 g of the excess sludge dry base is 0.01 to 0.02 g.

  Next, the reason why the chlorine dioxide is controlled so as to be an injection amount of 0.01 to 0.02 g per 1 g of the excess sludge dry base will be described. FIG. 2 shows the relationship between the amount of chlorine dioxide injected and the volume reduction rate of excess sludge, and the relationship between the amount of chlorine dioxide injected and the quality of treated water. The horizontal axis in Fig. 2 is the injection amount g of chlorine dioxide per gram of dry sludge base, and the left vertical axis is the volume reduction rate of excess sludge (volume reduction rate 1 is 100% reduction of excess sludge. The vertical axis on the right side shows the TOC (total organic carbon content) of the treated water, and the TOC increases as it goes up.

  First, looking at the relationship between the amount of chlorine dioxide injection and the volume reduction rate of excess sludge, the volume reduction rate gradually increases as the amount of chlorine dioxide injection to the excess sludge increases. The volume reduction rate suddenly increases from around 0.01 g of chlorine dioxide per gram, the volume reduction rate reaches 1 around 0.015 g of chlorine dioxide, and thereafter the volume reduction rate changes around 1. From this result, in order to achieve a sufficient volume reduction rate of the excess sludge by the solubilization treatment of chlorine dioxide, it is necessary to set the injection amount of chlorine dioxide per 1 g of the excess sludge dry base to 0.01 g or more. , 0.015 g or more is more preferable.

  On the other hand, looking at the relationship between the amount of chlorine dioxide injected and the quality of the treated water, as the amount of chlorine dioxide injected into the surplus sludge increases, the TOC in the treated water gradually increases. The TOC suddenly increases from around 0.02 g of chlorine dioxide per hit. From this result, in order to prevent deterioration of the quality of the treated water due to the solubilization treatment of chlorine dioxide, it is necessary to make the injection amount of chlorine dioxide per 1 g of the excess sludge dry base 0.02 g or less.

  As a result, when chlorine dioxide is used as a solubilizer, the amount of chlorine dioxide injected to efficiently reduce the volume of excess sludge without deteriorating the quality of the treated water is as follows: chlorine dioxide per 1 g of excess sludge dry base Is in the range of 0.01 to 0.02 g, preferably in the range of 0.015 to 0.02 g of chlorine dioxide per 1 g of dry base of excess sludge. Controlling the injection amount of chlorine dioxide within such a range can be achieved by using the automatic injection control mechanism 38 described above. Then, by injecting chlorine dioxide per gram of excess sludge into the range of 0.015 to 0.02 g, there is no excess or deficiency of the amount of chlorine dioxide injected into the excess sludge, so the quality of the treated water is deteriorated. It is possible to efficiently reduce the volume of excess sludge so that it does not occur. In addition, since there is no excess or deficiency in the amount of chlorine dioxide injected, unnecessary chlorine dioxide injection is eliminated, contributing to a reduction in running cost.

  FIG. 3 is an overall configuration diagram of the wastewater treatment system 10 incorporating the second embodiment of the excess sludge volume reduction device of the present invention, and the volume reduction device 14 provided with another automatic injection control mechanism 38. This is the case. Since the configuration of the wastewater treatment system 10 is the same as that of the first embodiment, the description thereof will be omitted, and the same devices and members will be described with the same reference numerals.

  The volume reduction device 14 in the second embodiment mainly includes a solubilization treatment tank 36 with a stirrer that solubilizes excess sludge with chlorine dioxide, and chlorine dioxide per gram of dry sludge of the excess sludge in the solubilization treatment tank 36. And an automatic injection control mechanism for injecting in a range of 0.01 to 0.02 g.

  The automatic injection control mechanism 38 measures the oxidation-reduction potential of excess sludge in the solubilization treatment tank 36 over time with an oxidation-reduction potentiometer 56 (ORP meter). The measurement may be continuous measurement or intermittent measurement. The measured value of the oxidation-reduction potential measured by the oxidation-reduction potentiometer is sent to the control means 46. And the control means 46 adjusts the opening degree of the automatic valve 54 of the injection piping 52 extended from the injection apparatus 48 so that a measured value may be in the range of 500-600 mV, and controls the injection amount of chlorine dioxide.

  FIG. 4 shows the relationship between the amount of chlorine dioxide injected into the solubilization treatment tank 36 and the oxidation-reduction potential (mV) of excess sludge measured by the oxidation-reduction potentiometer 56. As can be seen from FIG. 4, the redox potential when 0.01 g of chlorine dioxide is injected per gram of dry sludge base is about 500 mV, and the redox potential when 0.015 g of chlorine dioxide is injected is about 550 mV. Yes, the redox potential when 0.02 g of chlorine dioxide is injected is about 600 mV. Therefore, by measuring the oxidation-reduction potential in the solubilization treatment tank 36 and injecting chlorine dioxide from the injection device 48 so that the measured value falls within the range of 500 to 600 mV, chlorine dioxide per gram of the excess sludge dry base is obtained. Can be controlled in the range of 0.01 to 0.02 g. Thereby, the effect similar to 1st Embodiment can be acquired. Note that the automatic injection control mechanism 38 using the oxidation-reduction potential in FIG. 3 has a pH of the excess sludge to be solubilized when the pH of the organic wastewater flowing into the biological treatment tank 16 from the raw water pipe 26 is large. May also vary, which may affect the amount of chlorine dioxide injection. In this case, both the automatic injection control mechanism 38 using the sludge densitometer 40 described in FIG. 1 and the automatic injection control mechanism 38 using the oxidation-reduction potential are provided. Usually, the automatic injection control mechanism 38 using the oxidation-reduction potential is used. It is preferable to use the injection control mechanism 38 and switch to the automatic injection control mechanism 38 using the sludge concentration meter 40 when the pH fluctuation of the organic waste water is large.

  FIG. 5 is an overall configuration diagram of a wastewater treatment system 10 incorporating the third embodiment of the excess sludge volume reduction device of the present invention. Solubilization of excess sludge with chlorine dioxide and excess sludge with alkali are possible. This is the case where solubilization is used in combination. In addition, since the structure of the wastewater treatment system 10 is the same as that of 1st and 2nd embodiment, description is abbreviate | omitted and the same code | symbol is attached | subjected and demonstrated to the same apparatus and member.

  In the excess sludge volume reducing device 14 in the third embodiment, the excess sludge transferred to the excess sludge pipe 35 by the sludge transfer pump 34 is distributed by the first solubilizing pipe 60 and the second solubilizing pipe 60. The pipe 62 is divided into two. The excess sludge distributed to the first solubilization pipe 60 is sent to the first solubilization treatment tank 64 and solubilized with chlorine dioxide. The first solubilization treatment tank 64 is provided with the above-described chlorine dioxide automatic injection control mechanism 38 based on the oxidation-reduction potential, and the oxidation-reduction potential in the first solubilization treatment tank 64 is measured. Chlorine dioxide is injected from the injection device 48 so that the measured value falls within the range of 500 to 600 mV. Thereby, chlorine dioxide can be injected at an injection amount of 0.01 to 0.02 g per 1 g of the dry sludge base. On the other hand, surplus sludge distributed to the second solubilization pipe 62 is sent to the second solubilization treatment tank 66. In the second solubilization treatment tank 66, a pH meter 68 for measuring the pH of the excess sludge in the tank 66, an alkali tank 70 for storing an alkaline liquid, and the alkali tank 70 to the second solubilization treatment tank 66. An extended injection pipe 72, an automatic valve 74 provided in the injection pipe 72, and a stirrer 76 that stirs and mixes excess sludge in the tank 66 and the alkaline liquid are provided. Then, the opening degree of the automatic valve 74 is adjusted based on the pH value of the excess sludge measured by the pH meter, and the alkaline liquid is injected from the alkali tank 70 so that the pH of the excess sludge becomes 11.5-12. . Thereby, the excess sludge sent to the 2nd solubilization processing tank 66 is solubilized by the alkali.

  Next, the excess sludge solubilized in the first solubilization treatment tank 64 is sent to the mixing tank 82 via the first transfer pipe 80 by the first transfer pump 78 and the second solubilization treatment tank. The surplus sludge solubilized in 66 is sent to the mixing tank 82 through the second transfer pipe 86 by the second transfer pump 84. The mixing tank 82 is provided with a stirrer 88 and is solubilized with chlorine dioxide in the first solubilization treatment tank 64 and solubilized with acid in the acidic state and solubilized with alkali in the second solubilization treatment tank 66. Alkaline excess sludge is mixed and neutralized. Moreover, the pH meter 90 is provided in the mixing tank 82, pH of the excess sludge after mixing is measured, and it is monitored whether the measured value is in the range of 6.5-7.5. And when it does not enter into this pH range, it changes to the pH range of 6.5-7.5 by changing the distribution ratio to the 1st and 2nd solubilization processing tanks 64 and 66 in the distributor 58. Like that. By providing this mixing tank 82, it is possible to carry out a neutralization treatment necessary for returning surplus sludge to the biological treatment tank 16, so that the neutralizing agent for neutralizing acidic surplus sludge is also an alkaline surplus. There is no need for a neutralizing agent to neutralize sludge. Thereby, surplus sludge can be solubilized economically.

  The surplus sludge mixed in the mixing tank 82 is returned to the biological treatment tank 16 by the solubilized sludge return pump 92 through the solubilized sludge return pipe 94 and the raw water pipe 26. The solubilized surplus sludge returned to the biological treatment tank 16 is decomposed by the activated sludge as a nutrient source for the activated sludge in the biological treatment tank 16. As a result, the same effects as those of the first and second embodiments can be obtained, and the use of a neutralizing agent is eliminated, so that the running cost can be further reduced.

Overall configuration diagram of a wastewater treatment system incorporating the first embodiment of the excess sludge volume reduction device of the present invention Graph showing the relationship between the amount of chlorine dioxide injection and the volume reduction rate of excess sludge, and the amount of chlorine dioxide injection and treated water quality Overall configuration diagram of a wastewater treatment system incorporating the second embodiment of the excess sludge volume reducing device of the present invention Graph showing the relationship between the amount of chlorine dioxide injection and the redox potential Overall configuration diagram of a wastewater treatment system incorporating the third embodiment of the excess sludge volume reducing device of the present invention

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Waste water treatment system, 12 ... Biological treatment apparatus, 14 ... Volume reduction apparatus, 16 ... Biological treatment tank, 18 ... Solid-liquid separation tank, 20 ... Aeration pipe, 22 ... Air piping, 24 ... Blower, 26 ... Raw water piping 28 ... Raw water pump, 30 ... Water pipe, 31 ... Solubilized sludge return pump, 32 ... Sludge return pump, 34 ... Sludge transfer pump, 35 ... Excess sludge piping, 36 ... Solubilization tank, 37 ... Stirrer, 38 DESCRIPTION OF SYMBOLS ... Automatic injection | pouring control mechanism, 40 ... Sludge densitometer, 42 ... Converter, 44 ... Calculator, 46 ... Control means, 48 ... Injection | pouring apparatus, 50 ... Storage tank, 52 ... Injection piping, 54 ... Automatic valve, 56 ... Oxidation Reduction potentiometer (ORP meter), 58 ... distributor, 60 ... first solubilization piping, 62 ... second solubilization piping, 64 ... first solubilization treatment tank, 66 ... second solubilization treatment tank 68 ... pH meter, 70 ... Alkali tank, 72 ... Note Pipe 74 ... Automatic valve 76 ... Stirrer 78 ... First transfer pump 80 ... First transfer pipe 82 ... Mixing tank 84 ... Second transfer pump 86 ... Second transfer pipe 88 ... Stirrer, 90 ... pH meter, 92 ... Solubilized sludge return pump, 94 ... Solubilized sludge return pipe

Claims (2)

In the surplus sludge volume reduction method of reducing the excess sludge by solubilizing excess sludge generated when biologically treating organic wastewater in a biological treatment tank and returning it to the biological treatment tank,
Distributing the solubilized surplus sludge into two;
Solubilizing one of the distributed surplus sludge with chlorine dioxide;
Solubilizing the other surplus sludge distributed with an alkaline solution;
A step of mixing the acid surplus sludge solubilized with chlorine dioxide and the alkali surplus sludge solubilized with the alkaline solution and neutralizing them, and then returning to the biological treatment tank,
Measuring the pH of the mixed excess sludge;
Based on the measured results, changing the distribution ratio of the excess sludge before solubilization so that the pH of the mixed excess sludge falls within a predetermined range;
A method for reducing the volume of excess sludge, comprising: In the excess sludge volume reduction device that reduces the excess sludge by solubilizing excess sludge generated when biologically treating organic wastewater in a biological treatment tank and returning it to the biological treatment tank,
A distributing means for distributing the solubilized surplus sludge into two;
A first solubilization tank for solubilizing one of the distributed surplus sludge with chlorine dioxide;
A second solubilization tank for solubilizing the other surplus distributed sludge with an alkaline solution;
A mixing tank for mixing excess sludge solubilized in the first and second solubilization processing tanks;
A return line for returning the mixed excess sludge mixed in the mixing tank to the biological treatment tank,
The pH measuring means for measuring the pH of the mixed surplus sludge is provided, and the distributing means is for the surplus sludge before solubilization so that the pH of the mixed surplus sludge measured by the pH measuring means falls within a predetermined range. An apparatus for reducing the volume of excess sludge, characterized in that the distribution ratio is variable.

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