JP2007061773A - Organic sludge treatment method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic sludge treatment method and apparatus which can maintain an excellent quality of treated water discharged from a waste water treatment system by making the following return water free from biologically hardly decomposable substances and phosphorus components when digested liquid generated by anaerobically digesting organic sludge from the waste water treatment system is dehydrated, and treated water obtained by biologically treating the obtained dehydrated supernatant is returned to the waste water treatment system as return water. <P>SOLUTION: The organic sludge treatment method comprises a process for anaerobically digesting the organic sludge from the waste water treatment system, a process for adding a combination of two or more kinds of coagulants to the digested liquid generated by the above anaerobic digestion, and dehydrating the digested liquid, a process for biologically treating the dehydrated supernatant obtained by the above dehydration treatment, and a process for returning the treated liquid obtained by the above biological treatment to the waste water treatment system as the return water. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a method and apparatus for treating organic sludge, and dehydrates digestive juice produced by anaerobic digestion of organic sludge from a wastewater treatment system such as sewage treatment, A method for treating organic sludge, which prevents the return water from adversely affecting the quality of the treated water discharged from the waste water treatment system when the treated water obtained by the treatment is returned to the waste water treatment system as the return water. It relates to the device.

  In the sewage treatment facility, sewage is treated in a wastewater treatment system (sewage treatment system) equipped with a first sedimentation basin, biological reaction tank, and final sedimentation basin, while sludge stabilization, detoxification, and volume reduction in the sludge treatment system. Digestion liquid (digestion) produced by anaerobic digestion treatment of excess sludge generated in the final sedimentation basin and raw sludge produced in the initial sedimentation basin for the purpose of reducing (reducing amount) and recovering energy Sludge) is dewatered, and the resulting dewatered sludge (dehydrated cake) is taken out of the facility for incineration and landfill disposal. In addition, the dehydrated separation liquid obtained by dehydrating the digested liquid is generally returned to the inlet side of the first sedimentation basin of the wastewater treatment system as treated water obtained by biologically treating it. .

  In this case, in Patent Document 1, the sludge concentrated / separated liquid produced by gravity concentration of the raw sludge generated in the first sedimentation basin is guided to the sludge concentrated / separated liquid treatment tank for biological treatment, and organic substances such as COD components are removed. The treated water was returned to the first settling basin as return water, and the dehydrated separation liquid obtained by dehydrating the digested liquid produced by anaerobic digestion of excess sludge generated in the final settling basin ( The dehydrated filtrate is introduced into the dehydrated filtrate treatment tank for biological treatment, and the treated water that has undergone nitrification of ammonia nitrogen and removal of COD components is returned to the inlet side of the first sedimentation basin as return water. A processing method has been proposed.

  However, the dehydrated separation liquid obtained by dehydrating digestive juice produced by anaerobic digestion of organic sludge such as sewage sludge contains organic compounds that can be removed by biological treatment, as well as phosphorus components and normal organisms. Biologically difficult-to-decompose substances such as fibers and coloring components that are difficult to remove by treatment alone (refractory organic substances (persistible COD)) are included. Accordingly, the biologically degradable substance and the phosphorus component remain in the dehydrated separation liquid (dehydrated filtrate) without being removed even after biological treatment.

For this reason, conventionally, when the treated water obtained by biologically treating the dehydrated separation liquid is returned to the wastewater treatment system as the return water, the quality of the treated water discharged from the wastewater treatment system may be adversely affected. In particular, when organic sludge is solubilized by heat treatment prior to anaerobic digestion treatment, the amount of biologically degradable substances and phosphorus components in the return water increases, so the treatment is discharged from the wastewater treatment system. It was necessary to avoid adversely affecting the water quality.
JP 2004-97903 A (2nd page, FIG. 1)

  Then, the subject of this invention is dehydrating the digestive liquid produced by the anaerobic digestion treatment of the organic sludge from a wastewater treatment system, and the treated water obtained by biologically treating the obtained dehydrated separation liquid is used as the return water. When returning to the wastewater treatment system, it is possible to maintain the quality of the treated water discharged from the wastewater treatment system by preventing the returnable water from containing biologically degradable substances and phosphorus components as much as possible. Another object is to provide a method and apparatus for treating organic sludge.

  In order to solve the above problems, the present invention takes the following technical means.

  The invention according to claim 1 is a step of anaerobic digestion treatment of organic sludge from a wastewater treatment system, and a combination of two or more flocculants in the digestive juice produced by the anaerobic digestion treatment, A dehydration process, a biological process of the dehydrated separation liquid obtained by the dehydration process, and a process of returning the treatment liquid obtained by the biological process to the wastewater treatment system as return water. It is the processing method of the characteristic organic sludge.

  The invention according to claim 2 is the organic sludge treatment method according to claim 1, wherein the coagulant used in combination of two or more is at least a cationic inorganic coagulant and an amphoteric polymer coagulant or an anionic polymer coagulant. It is characterized by the combination.

  The invention of claim 3 is the organic sludge treatment method according to claim 1 or 2, characterized in that the biological treatment is a biological treatment by a nitrification denitrification method.

  The invention of claim 4 is the organic sludge treatment method according to claim 1, 2, or 3, further comprising a step of solubilizing the organic sludge as a pretreatment prior to the anaerobic digestion treatment. It is what.

  The invention of claim 5 is the organic sludge treatment method according to claim 4, characterized in that the solubilization treatment is a treatment for bringing the organic sludge into a solubilized state by heat treatment at high temperature and high pressure. is there.

  The invention according to claim 6 is a digester for anaerobic digestion treatment of organic sludge from a wastewater treatment system, and a combination of two or more flocculants in the digestive fluid produced in the digester, A dehydration device for dehydration, a biological treatment device for biological treatment of the dehydrated separation liquid obtained by the dehydration device, and a return water line for returning the treatment liquid obtained by the biological treatment device to the wastewater treatment system as return water It is an organic sludge processing apparatus characterized by including these.

  According to a seventh aspect of the present invention, in the organic sludge treatment apparatus according to the sixth aspect, the coagulant used in combination of two or more types is at least a cationic inorganic coagulant and an amphoteric polymer coagulant or an anionic polymer coagulant. It is characterized by the combination.

  The invention according to claim 8 is the organic sludge treatment apparatus according to claim 6 or 7, wherein the biological treatment apparatus has a nitrification tank and a denitrification tank.

  The invention of claim 8 is the organic sludge treatment apparatus according to claim 6, 7 or 8, wherein a sludge solubilization apparatus for solubilizing organic sludge from a wastewater treatment system is used as a pretreatment apparatus for the digestion tank. And solubilized sludge by the sludge solubilizer as organic sludge is supplied to the digester.

  The organic sludge treatment method or the organic sludge treatment apparatus of the present invention is a combination of two or more coagulants added to a digestion solution produced by anaerobic digestion of organic sludge generated in a wastewater treatment system. By dehydrating the product, the biodegradable substance and the phosphorus component contained in the digested liquid are transferred and taken into the dehydrated sludge separated from the digested liquid by dehydration. Therefore, since the dehydrated separation liquid separated from the digested liquid by dehydration contains almost no biologically degradable substances and phosphorus components, the treated water obtained by biological treatment of this dehydrated separated liquid is used as the return water for the wastewater treatment system. Even if it is returned to, the quality of the treated water discharged from the wastewater treatment system is not adversely affected, and the quality of the water can be maintained well.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a flowchart showing a schematic configuration of a sewage treatment facility equipped with an organic sludge treatment apparatus for carrying out the method according to the first embodiment of the present invention.

  As shown in FIG. 1, the sewage treatment facility includes a wastewater treatment system (sewage treatment system) including an initial sedimentation tank 101, a biological treatment tank 102, and a final sedimentation tank 103, and an organic sludge treatment apparatus as a sludge treatment system. It is comprised by. The organic sludge treatment apparatus includes concentration apparatuses 201 and 202, a digestion tank 203, a dehydration apparatus 204, a biological treatment apparatus 205, and a return water line 209.

  The sewage first flows into the settling basin 101, and the floating substances that are likely to settle in the first settling basin 101 are settled and removed, and then the organic matter that is dirt in the sewage is decomposed and removed by the action of microorganisms in the biological treatment tank 102. The activated sludge is settled in the final sedimentation basin 103, and the clean supernatant water is discharged as treated water.

  A part of the activated sludge settled in the final sedimentation basin 103 is returned to the biological treatment tank 102 as return sludge, and the remaining surplus sludge is reduced in volume, so that a concentration device such as a centrifugal concentrator or a flotation concentrator is used. (Mechanical concentrator) sent to 201 and concentrated to a solid concentration of about 2 to 5%. Similarly, the raw sludge from the first sedimentation tank 101 is sent to a concentration device 202 such as a gravity concentration tank and concentrated to a solid concentration of about 2 to 5% by gravity sedimentation.

  And the excess sludge and the raw sludge, which are the concentrated organic sludge, are anaerobically digested by the action of anaerobic bacteria such as acid-producing bacteria and methane-producing bacteria in the digestion tank 203, so that about 60% of methane is obtained. The digestion gas which is a mixed gas of about 40% of carbon dioxide is produced.

  Next, the digested liquid (digested sludge) generated by this anaerobic digestion treatment is guided to a dehydrator 204 composed of, for example, a belt press dehydrator. Examples of the dehydrator 204 include a centrifugal dehydrator, a screw press, a filter press, and a rotary pressure dehydrator in addition to the belt press dehydrator. In the dehydrating apparatus 204, a mixture obtained by adding two or more coagulants to the digested liquid and stirring and mixing is dehydrated. By using two or more types of flocculants in combination, there are advantages such as being able to cope with more components in the sludge and improving the cohesive force by balancing the charge. As a result, dewatering performance is improved, and more biologically degradable substances and phosphorus components are transferred into dewatered sludge separated from digestive juice by dehydration than when one type of flocculant is used alone. Can be captured. As a result, the dehydrated separation liquid (dehydrated filtrate) separated from the digestive juice by dehydration contains almost no biologically degradable substances and phosphorus components. It is sent to the biological treatment apparatus 205 that performs the treatment.

  In this case, the coagulant used in combination includes a cationic inorganic coagulant and an amphoteric polymer coagulant, a cationic polymer coagulant and a weak anionic polymer coagulant, a cationic inorganic coagulant and an anionic polymer coagulant, There are combinations such as, and select the appropriate one according to the properties of the digestive fluid (digested sludge). As the addition procedure, sludge usually has a negative charge. For example, first, a cationic inorganic flocculant is added to the digested liquid to neutralize the charge to generate primary floc, and then the amphoteric polymer flocculant. Alternatively, the flocs may be further aggregated by adding an anionic polymer flocculant. In this embodiment, first, a highly anionic digestive liquid is neutralized with a cationic inorganic flocculant, and then a mixture obtained by adding an amphoteric polymer flocculant having high cohesive force to the digested liquid and stirring and mixing is dehydrated. It supplies to the apparatus 204.

  The biological treatment apparatus 205 to which the dehydration separation liquid from the dehydration apparatus 204 is supplied is a combination of a circulation type nitrification denitrification method and a membrane separation method, and includes a denitrification tank (anoxic tank) 206, a nitrification tank (aerobic tank). 207, and a membrane separator 208 immersed in the nitrification tank 207.

  In the nitrification tank 207, ammonia nitrogen flowing in through the denitrification tank 206 is oxidized by the action of nitrite bacteria and nitrate bacteria to become nitrate nitrogen, and this nitrate nitrogen is circulated and returned to the denitrification tank 206 as a nitrification liquid. . In the denitrification tank 206, nitrate nitrogen is reduced by the action of the denitrifying bacteria and released into the atmosphere as nitrogen gas, and organic substances in the dehydrated separation liquid flowing into the denitrification tank 206 are oxidized by this denitrification reaction. And consumed. The excess sludge in the nitrification tank 207 is returned to the digestion tank 203 and the denitrification tank 206. After nitrifying and denitrifying the dehydrated separation liquid in this way, the clear treated water separated by solid-liquid separation by the membrane separation device 208 is returned to the inlet side of the first sedimentation tank 101 through the return water line 209 as return water. The

  As described above, in the treatment of organic sludge from the wastewater treatment system for the purpose of volume reduction or the like, two or more kinds of flocculants are added to the digested liquid produced by the anaerobic digestion treatment. Since the addition of a cationic inorganic flocculant and an amphoteric polymer flocculant is dehydrated, the dewatering performance is improved compared to the case of using a single flocculant alone. More biodegradable substances and phosphorus components can be transferred and incorporated into the sludge. Therefore, since the dehydrated separation liquid separated from the digested liquid by dehydration contains almost no biologically degradable substances and phosphorus components, the wastewater treatment system uses the treated water obtained by biological treatment of this dehydrated separated liquid as the return water. Even if it is returned to, the quality of the treated water discharged from the wastewater treatment system is not adversely affected, and the quality of the water can be maintained well.

  FIG. 2 is a flowchart showing a schematic configuration of a sewage treatment facility equipped with an organic sludge treatment apparatus for carrying out the method according to the second embodiment of the present invention. Here, except that a high concentration concentrator 210 and a sludge solubilizer 211 are added upstream of the digester 203, it is the same as the organic sludge treatment apparatus in FIG. Are denoted by the same reference numerals, description thereof is omitted, and different points will be mainly described.

  The high-concentration concentrator 210 is composed of, for example, a centrifugal concentrator, and is supplied with the concentrated excess sludge from the concentrator 201 and the concentrated raw sludge from the concentrator 202. It is a concentration device that concentrates to about 15%. The sludge solubilizer 211 includes a buffer tank A, a reactor, a buffer tank B, and a sludge cooler (all of which are not shown).

  In the sludge solubilizer 211, the high-concentration concentrated sludge from the high-concentration concentrator 210 is received in the buffer tank A, and the high-concentration sludge is preheated to about 100 ° C. by the excess steam of the reactor in the buffer tank A. Next, sludge from the buffer tank A is introduced into the reactor, and steam is used in the reactor at high temperature and high pressure (for example, temperature: 120 to 200 ° C., pressure: 0.2 to 1.5 MPaG, more preferably, temperature 160 Hold for about 30 minutes under the condition of (° C., pressure of about 0.6 MPaG) to destroy the cell wall in the sludge and make the sludge solubilized. The solubilized sludge discharged from the reactor is temporarily stored in the buffer tank B, then the normal pressure solubilized sludge from the buffer tank B is supplied to the sludge cooler, and adjusted to a temperature suitable for digestion from the sludge cooler. The solubilized sludge (solid content concentration of about 10%) is supplied to the digester 203.

  In the digestion tank 203, digested gas is generated by anaerobic digestion of the solubilized sludge. In this case, as a pretreatment for the anaerobic digestion treatment, the sludge is solubilized by the high-concentration concentrator 210 and the sludge solubilizer 211 by heat treatment under high temperature and high pressure using steam as described above. Therefore, the biodegradability in the digestion tank 203 is increased, so that the amount of digestion gas generated is increased and the amount of organic substances in the sludge is reduced compared with the case where the solubilization treatment is not performed. The amount of solids decreases.

  Next, the digested liquid (digested sludge) generated by this anaerobic digestion treatment is guided to the dehydrating apparatus 204, and in the dehydrating apparatus 204, two or more kinds of flocculants are added to the digested liquid. What added and used together the inorganic flocculant and the amphoteric polymer flocculent is dehydrated. As a result, in the same manner as in the first embodiment, the biodegradable substance and the phosphorus component contained in the digested liquid are transferred and taken into the dehydrated sludge separated from the digested liquid by dehydration. Can do. In this dehydration treatment, the water content of the dewatered sludge by dehydration can be reduced by the effect of reducing the amount of solids in the digested liquid by the solubilization treatment, compared to the case of not solubilizing the dehydrated sludge, For example, it can be reduced to about 65% (when not solubilized, about 80%). The dehydrated separation liquid separated from the digestive juice by the dehydration treatment by adding the cationic inorganic flocculant and the amphoteric polymer flocculant contains almost no biologically degradable substances and phosphorus components. The liquid is sent to a biological treatment apparatus 205 that performs biological treatment by a circulating nitrification denitrification method. Therefore, even if the treated water obtained by biologically treating this dehydrated separation liquid is returned to the wastewater treatment system as return water, the quality of the treated water discharged from the wastewater treatment system will not be adversely affected. It can be maintained well.

  As described above, in the method according to the second embodiment, the biological difficulty in the digestive juice generated by the anaerobic digestion treatment is obtained by performing the solubilization treatment by heat treatment as compared with the case of the solubilization treatment not using heat treatment. Even if the degradable substances increase, two or more kinds of flocculants are added to the digestive juice, and in this embodiment, a cationic inorganic flocculant and an amphoteric polymer flocculant are added in combination and mixed with stirring. Since the thing is dehydrated, the biologically degradable substance and the phosphorus component contained in the digested liquid can be transferred and taken into the dehydrated sludge separated from the digested liquid by dehydration. Therefore, in the same manner as in the method of the first embodiment, the dehydrated separation liquid separated from the digested liquid by dehydration contains almost no biologically degradable substance and phosphorus component. Even if the treated water obtained in this manner is returned to the wastewater treatment system as return water, the quality of the treated water discharged from the wastewater treatment system is not adversely affected, and the water quality can be maintained well.

  Prior to the anaerobic digestion treatment, the organic sludge from the wastewater treatment system is made into a solubilized state by heat treatment under high temperature and high pressure using steam, and the solubilized organic sludge is treated as a pretreatment. Because it is anaerobic digestion treatment, it improves digestibility (reducing the amount of solids in the digestion tank) and improves the dewaterability of the digestive fluid (reduced water content of dewatered sludge) compared to the case without solubilization treatment. Conversion) has the advantage that the amount of dewatered sludge can be almost halved. As for the solubilization treatment, heat treatment under high temperature and high pressure is used in this embodiment, but chemical treatment with an oxidizing agent such as ozone or alkali is also applicable.

In each of the first and second embodiments described above, in nitrification denitrification in biological treatment of a dehydrated separation liquid, ammonia nitrogen in the dehydrated separation liquid is aerobic and passes through nitrite nitrogen to nitrate nitrogen. Nitric acid-type nitrification denitrification is performed to oxidize and denitrify, but this is not restrictive, and ammonia nitrogen is oxidized at the nitrite nitrogen stage and denitrified. Nitrite-type nitrification denitrification may be performed. In the second embodiment, a centrifugal concentrator is used as the high concentration concentrator 210. However, a screw press or a rotary pressure concentrator can also be applied. Furthermore, as is well known, the biological treatment tank 102 constituting the wastewater treatment system is usually activated sludge method, AO method (anaerobic-aerobic method) or A ₂ O method (anaerobic-anoxic-aerobic method). It is adopted.

It is a flowchart which shows schematic structure of the sewage treatment facility provided with the processing apparatus of the organic sludge which implements the method by the 1st Embodiment of this invention. It is a flowchart which shows schematic structure of the sewage treatment facility provided with the processing apparatus of the organic sludge which enforces the method by the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... First sedimentation tank 102 ... Biological treatment tank 103 ... Final sedimentation tank 201,202 ... Concentration apparatus 203 ... Digestion tank 204 ... Dehydration apparatus 205 ... Biological treatment apparatus 206 ... Denitrification tank 207 ... Nitrification tank 208 ... Membrane separation apparatus 209 ... Return Flowing water line 210 ... High concentration concentrator 211 ... Sludge solubilizer

Claims (9)

  A step of anaerobically digesting organic sludge from a wastewater treatment system, a step of adding a combination of two or more flocculants to the digestive fluid produced by the anaerobic digestion treatment, and dehydrating the digested solution; A step of biologically treating the dehydrated separation liquid obtained by the dehydration treatment, and a step of returning the treatment liquid obtained by the biological treatment to the wastewater treatment system as return water. Processing method.   The treatment of organic sludge according to claim 1, wherein the coagulant used in combination of two or more is at least a combination of a cationic inorganic coagulant and an amphoteric polymer coagulant or an anionic polymer coagulant. Method.   The method for treating organic sludge according to claim 1 or 2, wherein the biological treatment is a biological treatment by a nitrification denitrification method.   The organic sludge treatment method according to claim 1, further comprising a step of solubilizing the organic sludge as a pretreatment prior to the anaerobic digestion treatment.   5. The organic sludge treatment method according to claim 4, wherein the solubilization treatment is a treatment for bringing the organic sludge into a solubilized state by heat treatment at high temperature and high pressure.   A digester for anaerobic digestion of organic sludge from a wastewater treatment system, a dehydrator for adding a combination of two or more flocculants to the digestive juice produced in the digester, and dehydrating the digested solution; A biological treatment device for biologically treating the dehydrated separation liquid obtained by the dehydration device, and a return water line for returning the treatment liquid obtained by the biological treatment device to the wastewater treatment system as return water. Organic sludge treatment equipment.   The organic sludge treatment according to claim 6, wherein the coagulant used in combination of two or more is a combination of at least a cationic inorganic coagulant and an amphoteric polymer coagulant or an anionic polymer coagulant. apparatus.   The said biological treatment apparatus has a nitrification tank and a denitrification tank, The processing apparatus of the organic sludge of Claim 6 or 7 characterized by the above-mentioned.   9. The organic sludge treatment apparatus according to claim 6, 7 or 8, comprising a sludge solubilization apparatus for solubilizing organic sludge from a wastewater treatment system as a pretreatment apparatus for the digestion tank, wherein the digestion tank is organically treated. An organic sludge treatment apparatus, characterized by supplying solubilized sludge by the sludge solubilizer as a soluble sludge.

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