JP4599955B2 - How to reduce excess sludge - Google Patents

Description

  The present invention relates to a surplus sludge volume reduction method, and more particularly to a surplus sludge volume reduction method in which surplus sludge generated by biological treatment of organic waste water is solubilized using chlorine dioxide.

  In recent years, as a method of reducing the volume of excess sludge generated when biologically treating wastewater in a biological treatment tank, it is generated by solubilizing part of the returned sludge and converting it to BOD and returning it to the biological treatment tank. Developments have been made to reduce the amount.

  As a method of solubilizing excess sludge, there is a method of mechanically destroying the cell walls of microorganisms present in the sludge by a wet mill, a disk, or ultrasonic waves. Further, methods of chemically solubilizing such as ozone method and acid or alkali treatment method, methods of utilizing living organisms such as thermophilic bacteria method, etc. are also being studied.

  Conventionally, among the methods described above, a method of solubilizing sludge by the ozone method has been widely used as one showing stable volume reduction performance (see Patent Document 1).

  In addition, a method for reducing the volume of sludge using various disinfectants as in Patent Document 2 has been proposed, and an example in which chlorine dioxide is used as a disinfectant is given.

Chlorine dioxide is originally widely used as a bleaching agent and bactericidal agent because of its strong oxidizing power. Therefore, if chlorine dioxide is used as a sludge solubilizer as in Patent Document 3, the running cost is relatively low. Become. In this case, gas or the like harmful to the human body is not generated at the time of treatment unlike ozone treatment, so that the cost required for the abatement equipment can be eliminated. In addition, since there is not much foaming of sludge during processing, there is also an advantage that handling is easy.
JP 7-88495 A Japanese Patent Laid-Open No. 11-147801 JP 2003-260491 A

  By the way, chlorine dioxide used for solubilization of sludge by the method of Patent Document 3 is unstable and difficult to store for a long time. Therefore, chlorine such as sodium chlorite or sodium chlorate is used when chlorine dioxide is used. In general, the acid is used as a raw material.

  However, since the produced chlorine dioxide is gaseous, in order to efficiently contact and react with the sludge to be solubilized, it is necessary to devise measures such as reacting in a pressurized state or circulating the gas. Is done. For this reason, there is a drawback that the apparatus becomes complicated.

  Further, when chlorine dioxide is produced from chloric acid as a raw material, oxygen gas is generated as a by-product. When oxygen gas is present when chlorine dioxide is reacted with sludge, there is a problem that troubles such as sludge foaming and scum generation increase.

  The present invention has been made in view of such circumstances, and it is possible to efficiently perform sludge solubilization with a simple apparatus configuration, and it is easy to maintain and manage wastewater treatment, and to reduce running costs. The purpose is to provide a volume reduction method.

  In order to achieve the above object, the invention described in claim 1 solubilizes surplus sludge generated when biological wastewater is biologically treated with activated sludge in a biological treatment tank, and returns it to the biological treatment tank. In the excess sludge volume reduction method for reducing the volume of generated excess sludge, a mixed gas of chlorine dioxide and oxygen is generated using chloric acid as a raw material, and the mixed gas is mixed with the treated water treated in the biological treatment tank The chlorine dioxide is dissolved in the treated water, oxygen gas is separated from the treated water, and the solubilized treatment is performed by mixing the treated water in which the chlorine dioxide gas is dissolved with the excess sludge. It is characterized by that.

  According to the present invention, a mixed gas in which chlorine dioxide and oxygen are mixed using chloric acid as a raw material is generated, mixed with the treated water obtained by biological treatment, and only oxygen gas is separated from the treated water. After that, it was made to react with a part of activated sludge. This eliminates the need to supply chlorine dioxide to the sludge in a gasified state, so there is no need for a complicated device configuration such as a pressurized type or gas circulation type, thus reducing the initial cost required for sludge volume reduction. be able to.

  Moreover, since oxygen gas as a by-product is reacted with sludge in a state where it is separated and removed, sludge foaming and scum generation during sludge solubilization can be suppressed.

  The invention described in claim 2 is characterized in that the solubilized sludge subjected to the solubilization process described in claim 1 is aerated using the separated oxygen gas.

  According to claim 2, the oxygen required for oxidation with respect to the BOD component in the solubilized sludge increased by the oxidation or solubilization of the sludge with chlorine dioxide is efficiently solubilized by aeration of oxygen gas. Can be supplied to sludge. Therefore, the aeration load required for the biological treatment tank can be reduced.

  The invention according to claim 3 is characterized in that the aeration treatment is performed after mixing part of the returned sludge to be returned to the biological treatment tank with respect to the solubilized sludge according to claim 2. .

  According to the third aspect, the sludge BODized with chlorine dioxide is biologically treated with the mixed active return sludge. Thereby, the increase in BOD load in a biological treatment tank, the accompanying increase in aeration load in a biological treatment tank, and the deterioration of the quality of treated water can be prevented.

  As described above, according to the surplus sludge volume reduction method according to the present invention, chlorine dioxide produced using chloric acid as a raw material is mixed with sludge in a state where oxygen gas is removed after mixing in treated water. Therefore, the sludge can be efficiently solubilized with a simple equipment configuration, and the generation of sludge foaming and scum can be suppressed. Thereby, while maintaining and managing wastewater treatment, it is possible to reduce the volume of excess sludge with reduced initial costs and running costs.

  Hereinafter, a preferred embodiment of the method for reducing excess sludge according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is an explanatory diagram showing the configuration of a wastewater treatment system 100 according to the first embodiment that suitably uses the excess sludge volume reduction method of the present invention.

  As shown in the figure, the wastewater treatment system 100 is mainly composed of an excess sludge solubilizer 10, a biological treatment tank 12, and a sedimentation tank 14. Organic wastewater such as sewage is first supplied to the biological treatment tank 12 through the supply pipe 16 and aerobically in a state of being agitated with the internal activated sludge by being aerated by the aeration means 18 provided at the bottom. Biologically processed. The treated water thus biologically treated is subjected to solid-liquid separation of sludge and treated water in the sedimentation basin 14. In the settling tank 14, the separated treated water is discharged out of the system from the discharge pipe 20, while the separated sludge is returned from the bottom to the biological treatment tank 12 through the sludge return pipe 22 as return sludge. The sludge return pipe 22 is branched by a sludge extraction pipe 24, and a part of the return sludge passing through the sludge return pipe 22 is extracted and sent to the surplus sludge solubilizer 10.

  The surplus sludge solubilizer 10 is mainly composed of a raw sludge tank 28, a reaction tank 30, and a chlorine dioxide supply unit 32.

  The sludge extracted from the sludge return pipe 22 through the sludge extraction pipe 24 is sent to the raw sludge tank 28 and temporarily stored. The stored sludge is supplied to the reaction tank 30 through the sludge transfer pipe 36 by driving the sludge transfer pump 34. In the reaction tank 30, the sludge is solubilized by reacting with the chlorine dioxide by supplying chlorine dioxide from the chlorine dioxide supply unit 32 while mechanically stirring the sludge supplied to the tank with the stirring means 38 attached. To do. The solubilized sludge solubilized in this way is returned to the biological treatment tank 12 via the solubilized sludge return pipe 40.

  In the chlorine dioxide supply unit 32, sodium chlorate, sulfuric acid, and hydrogen peroxide are supplied from the sodium chlorate tank 42, the sulfuric acid tank 44, and the hydrogen peroxide tank 46 to the chlorine dioxide generation tank 48. At the same time, the treated water pump 50 installed on the upper surface of the settling basin 14 is driven and treated water is supplied to the chlorine dioxide generation tank 48 via the treated water supply pipe 52 and mixed. Thereby, the mixed gas which chlorine dioxide and oxygen mixed in the chlorine dioxide generation tank 48 is produced | generated, and it sends to the oxygen separation tank 54 in the state mixed with the treated water. In the oxygen separation tank 54, undissolved oxygen gas is separated from the treated water and exhausted from the upper exhaust pipe 56 to the atmosphere, while the treated water containing chlorine dioxide is reacted via the chlorine dioxide supply pipe 58. Supply to tank 30.

  Next, the operation of the excess sludge volume reduction method of the present invention will be described using the wastewater treatment system 100 according to the first embodiment configured as described above.

  Various sludge solubilization methods have been studied in order to reduce excess sludge, and one of them is a method of oxidizing with chlorine dioxide.

  Chlorine dioxide is widely used as an inexpensive bleaching and sterilizing oxidizer using sodium chlorite and sodium chlorate as raw materials, and has a sterilizing power 2.6 times that of chlorine. Further, if the concentration of chlorine dioxide gas in the air is 15 vol% or more, there is a risk of explosion, and it is necessary to keep it at 0.1 ppm or less for safety and health. Moreover, about 10 g of chlorine dioxide can be dissolved in 1 L of 20 ° C., but safety is desired to be used at 8 g / L or less in terms of disaster prevention guidelines.

  When chlorine dioxide is produced using sodium chlorate, sulfuric acid, and hydrogen peroxide, it is produced by reacting according to the chemical formula shown in Chemical Formula 1.

(Chemical formula 1) 2NaClO ₃ + H ₂ SO ₄ + H ₂ O ₂ → 2ClO ₂ + O ₂ + Na ₂ SO ₄ + 2H ₂ O
According to the above formula, 2 mol of chlorine dioxide and 1 mol of oxygen gas are generated from 2 mol of sodium chlorate. Oxygen gas also has an oxidizing power, but a stronger oxidizing power is required for solubilization of sludge. Therefore, as shown in the chemical formula shown in Chemical Formula 2, oxygen radicals are generated from the generated chlorine dioxide to cause strong oxidation. Thus, the oxidizing power by radicalization of chlorine dioxide is utilized rather than oxygen gas for solubilization of sludge.

(Chemical formula 2) ClO ₂ → Cl ⁻ + 2O ^.
However, if chlorine dioxide is used for sludge solubilization in the gaseous state, it is in the gaseous state, so the contact efficiency with sludge is low and the solubilization efficiency is low, and problems with wastewater treatment such as sludge foaming and scum generation. The problem of inviting factors that cause In addition, it is necessary to make the entire sludge solubilization equipment explosion-proof, and in order to improve the contact efficiency between chlorine dioxide and sludge, equipment that performs solubilization treatment as a pressurized type or a gas circulation type is required. There is a disadvantage that the initial cost increases.

  In the present invention, when raw materials are added to produce a mixed gas in which chlorine dioxide and oxygen are mixed, treated water is supplied simultaneously. As a result, water-soluble chlorine dioxide generated in the form of gas can be contained in the treated water to make a solution, so that the contact efficiency with sludge can be easily improved at low cost, and it is necessary in the form of gas. Explosion-proof equipment, pressurization equipment, gas circulation equipment, and the like are no longer necessary, so that the initial cost required for sludge solubilization can be greatly reduced. Moreover, since treated water is used, running cost can be suppressed. Furthermore, since oxygen gas is removed before being added to the sludge, it is possible to effectively prevent sludge foaming and scum generation. Thereby, volume reduction of excess sludge can be performed efficiently, without affecting the maintenance management of wastewater treatment.

  FIG. 2 is an explanatory diagram showing the configuration of a wastewater treatment system 300 according to the second embodiment that suitably uses the excess sludge volume reduction method of the present invention. In addition, about the apparatus and member similar to the waste water treatment system 100 which is 1st Embodiment shown in FIG. 1, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

  As shown in FIG. 2, the waste water treatment system 300 is different from the waste water treatment system 100 of FIG. 1 in that an oxygen aeration tank 60 is provided on the downstream side of the reaction tank 30 and an exhaust pipe 56 of the oxygen separation tank 54 is oxygenated. It exists in the point comprised by installing in the bottom part of the aeration tank 60. Therefore, in the oxygen aeration tank 60, the oxygen gas separated in the oxygen separation tank 54 is aerated from the bottom with respect to the sludge solubilized in the reaction tank 30. The sludge that has been aerated for a predetermined time in the oxygen aeration tank 60 is returned to the biological treatment tank 12.

  When the sludge is solubilized with chlorine dioxide in the reaction tank 30, the amount of the BOD component contained in the returned solubilized sludge increases. Therefore, if it is returned to the biological treatment tank 12 as it is, it will exceed the appropriate BOD load for the biological treatment capacity depending on the return amount of the solubilized sludge. It may cause water quality deterioration such as pollution. Therefore, in the present invention, an oxygen aeration tank 60 is provided between the reaction tank 30 and the biological treatment tank 12, and the sludge solubilized in the reaction tank 30 is aerated before flowing into the biological treatment tank 12. A part of oxygen required for oxidation can be efficiently supplied in advance to the BOD component contained in the solubilized sludge. If this aeration is performed by normal air aeration, the amount of oxygen is only 1/5 of the total, and thus the efficiency is low. However, in the present invention, oxygen gas, which is a by-product generated when chlorine dioxide is generated, is used for aeration. Therefore, oxygen can be supplied efficiently with little power.

  The oxygen gas to be aerated is not limited to an oxygen concentration of 100%, and may be supplied as oxygen-rich air mixed with outside air.

  FIG. 3 is an explanatory diagram showing a configuration of a wastewater treatment system 500 according to a third embodiment that suitably uses the excess sludge volume reduction method of the present invention.

  As shown in FIG. 3, the wastewater treatment system 500 is substantially the same as the wastewater treatment system 300 of FIG. 2, but a return sludge extraction pipe 64 is additionally provided in the return sludge pipe 22 to extract a part of the return sludge. Thus, the oxygen aeration tank 60 is used. Therefore, in the oxygen aeration tank 60, the oxygen gas separated from the oxygen separation tank 54 is aerated from the bottom in a state where the solubilized sludge from the reaction tank 30 and the extracted return sludge are mixed.

  It has been found that in the reaction tank 30, the sludge activity is almost lost due to the solubilization of chlorine dioxide. This is because solubilized sludge is because microorganisms in activated sludge have been killed by the oxidizing power of chlorine dioxide, but when mixed with return sludge having activity against solubilized sludge and aerated, it becomes solubilized sludge. On the other hand, biological treatment is performed. In this case, by supplying oxygen gas, the activity of microorganisms present in the mixed return sludge can be increased, so that an efficient biological treatment can be performed on the BOD component in the solubilized sludge. .

  In the above-described wastewater treatment systems 100, 300, and 500, the number, size, shape, and the like of each device and member used are not particularly limited.

  Moreover, in the wastewater treatment system 100, although the mechanical type was mentioned as an example as the stirring means 38 of the reaction tank 30, it is not specifically limited. As in the wastewater treatment systems 300 and 500 of FIGS. 2 and 3, stirring by aeration may be performed, or ultrasonic waves, vibrations, or the like may be used.

  Furthermore, in the wastewater treatment system 500, the independent oxygen aeration tank 60 is provided to mix the returned sludge and the solubilized sludge and aerate the oxygen gas, but is not particularly limited. The biological treatment tank 12 may be partitioned so that water can be passed in the vertical direction, and the returned sludge and the solubilized sludge may be introduced into the tank on the upstream side and aerated. Thereby, since installation of the independent oxygen aeration tank 60 becomes unnecessary, initial cost and installation space can further be reduced.

In Examples, RUN 1 to 3 which are wastewater treatment tests for solubilizing sludge were performed in order to confirm the volume reduction effect by the excess sludge volume reduction method of the present invention.

  RUN1 uses the method of the present invention in which the generated mixed gas of chlorine dioxide and oxygen is dissolved in the biologically treated water, and after separating the oxygen gas, it is mixed with a part of the returned sludge and solubilized. Wastewater treatment was performed continuously for one month.

  On the other hand, RUN2 was subjected to wastewater treatment continuously for one month using a method of solubilizing treatment by adding and mixing the generated mixed gas of chlorine dioxide and oxygen to a part of the returned sludge as it is. .

  Moreover, RUN3 performed the waste water treatment continuously for one month using the method of returning without performing solubilization processing with respect to the return sludge as a comparative example.

  The result is shown in FIG. FIG. 4 is a graph showing the sludge volume reduction rate in RUN1 and RUN2. In addition, the sludge volume reduction rate described here has shown the ratio% of the sludge quantity of RUN1 or 2 with respect to the sludge quantity of RUN3 which is a comparative example.

  According to the graph of FIG. 4, the sludge volume reduction rate of RUN1 was 80%, whereas the sludge volume reduction rate of RUN2 was about 75%. However, in RUN2, sludge foaming remarkably, and complicated operations increase in management of wastewater treatment such as foam recovery and cleaning, and problems for practical use remain. On the other hand, in RUN1, foaming etc. like RUN2 were not seen at all. The difference in the sludge volume reduction rate between RUN1 and RUN2 was that the sludge solubilization in RUN2 was performed at atmospheric pressure instead of being pressurized. It seems that a large percentage of the product was released into the atmosphere without being reacted.

  From the above, even from the viewpoint of sludge volume reduction performance and wastewater treatment maintenance management, the generated chlorine dioxide is dissolved in water and oxygen is separated and mixed with sludge for oxidation / solubilization reaction. Turned out to be excellent. Moreover, in order to produce sludge volume reduction performance equivalent to RUN1 by the method of RUN2, it is thought that it is necessary to pressurize sludge solubilization or to circulate chlorine dioxide gas. Since RUN1 does not require them, the device configuration can be simplified and the initial cost can be reduced.

Explanatory drawing which showed the structure of the waste water treatment system which is 1st Embodiment which used the surplus sludge volume reduction method of this invention suitably. Explanatory drawing which showed the structure of the waste water treatment system which is 2nd Embodiment which used the surplus sludge volume reduction method of this invention suitably. Explanatory drawing which showed the structure of the waste water treatment system which is 3rd Embodiment which used the surplus sludge volume reduction method of this invention suitably. Graph showing the relationship between oxygen gas separation and excess sludge volume reduction rate

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Surplus sludge solubilization apparatus, 12 ... Biological treatment tank, 14 ... Sedimentation basin, 16 ... Supply pipe, 18 ... Aeration means, 20 ... Discharge pipe, 22 ... Sludge return pipe, 24 ... Sludge extraction pipe, 28 ... Raw sludge Tank, 30 ... Reaction tank, 32 ... Chlorine dioxide supply unit, 34 ... Sludge transfer pump, 36 ... Sludge transfer pipe, 38 ... Stirring means, 40 ... Solubilized sludge return pipe, 42 ... Sodium chlorate tank, 44 ... Sulfuric acid Tank, 46 ... hydrogen peroxide tank, 48 ... chlorine dioxide generation tank, 50 ... treated water pump, 52 ... treated water supply pipe, 54 ... oxygen separation tank, 56 ... exhaust pipe, 58 ... chlorine dioxide supply pipe, 60 ... oxygen aeration tank, 62 ... oxygen gas supply blower, 64 ... return sludge extraction pipe, 100, 300, 500 ... wastewater treatment system

Claims (3)

Surplus sludge volume reduction method for reducing excess sludge generated by solubilizing surplus sludge generated when biologically treating organic wastewater with activated sludge in a biological treatment tank and returning it to the biological treatment tank In
Producing a mixed gas of chlorine dioxide and oxygen using chloric acid as a raw material,
The mixed gas is mixed with the treated water treated in the biological treatment tank to dissolve the chlorine dioxide in the treated water, and oxygen gas is separated from the treated water,
The surplus sludge volume reduction method characterized by performing the said solubilization process by mixing the treated water in which the said chlorine dioxide gas melt | dissolved with the said surplus sludge.   The excess sludge volume reduction method according to claim 1, wherein the solubilized sludge subjected to the solubilization treatment is subjected to an aeration treatment using the separated oxygen gas.   The excess sludge volume reduction method according to claim 2, wherein a part of the returned sludge to be returned to the biological treatment tank is mixed with the solubilized sludge and then the aeration treatment is performed.

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