Sludge Treatment System

Abstract

To provide a sludge treatment system that integrates an undigested treatment system for treating easily-dewaterable sludge and a digestion treatment system for treating difficult-to-dewaterable sludge.SOLUTION: In a sludge treatment system that dewaters easily-dewaterable sludge and difficult-to-dewaterable sludge, fibrous materials are collected from an easily-dewaterable sludge treatment system and added to the difficult-to-dewaterable sludge in the treatment system for dewatering, and by transferring the digested and dewatered filtrate of the difficult-to-dewaterable sludge to the easily-dewaterable sludge treatment system and bringing it into contact with excess sludge generated in the easily-dewaterable sludge treatment system, contact stabilization treatment is carried out. Thereby, dewaterability of the difficult-to-dewaterable sludge can be improved, and a portion of a nitrogen content and phosphorus in the digested and dewatered filtrate can be removed.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a sludge treatment system that utilizes different sludge treatment systems to dewater difficult-to-dewaterable sludge and treats the digested and dewatered filtrate of the difficult-to-dewaterable sludge. [Background technology]

[0002] Conventionally, in a typical water treatment system at a sewage treatment plant, the water to be treated flowing into the treatment plant is separated by settling in a primary settling tank, the separated supernatant water is biologically treated in a reaction tank supplied with oxygen, and then the separated supernatant water is separated by settling in a final settling tank, disinfected, and then discharged into a river or the like. Meanwhile, a sludge treatment system mixes the primary settling sludge extracted from the primary settling tank with the excess sludge generated in the final settling tank, and then separates the resulting mixed raw sludge into solid and liquid in a dehydrator to produce a dehydrated cake. There is also known a sludge treatment system in which the mixed raw sludge generated by the above flow is anaerobically digested in a digestion tank to reduce the volume, and the resulting digested sludge is separated into solid and liquid in a dehydrator.

[0003] Figure 7 of Patent Document 1 shows a flow chart for treating mixed raw sludge, which is a mixture of raw sludge withdrawn from a primary sedimentation tank and excess sludge generated in a final sedimentation tank. The technology disclosed involves recovering fiber from the raw sludge withdrawn from the primary sedimentation tank and adding fiber to the mixed sludge consisting of raw sludge thickened by gravity in the upstream stage of the dehydrator and excess sludge thickened mechanically.

[0004] Figure 1 of Patent Document 1 shows a flow chart for treating digested sludge produced by digesting raw sludge withdrawn from a primary sedimentation tank and excess sludge generated in a final sedimentation tank in a digestion tank. The figure discloses technology for recovering fiber from the raw sludge withdrawn from the primary sedimentation tank and adding fiber to the digested sludge upstream of the dehydrator.

[0005] Patent Document 2 discloses a technology in which sewage return water generated by subjecting digested sludge generated from multiple sewage treatment plants to processes such as concentration and dehydration is mixed with activated return sludge in a contact stabilization tank to adsorb and remove organic matter, nitrogen, and phosphorus. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6146665 [Patent Document 2] Patent No. 2704109 Summary of the Invention [Problem to be solved by the invention]

[0007] Conventional sludge treatment systems are not problematic if they only have a mixed raw sludge flow, but in recent years, an increasing number of treatment plants have been equipped with digestion equipment to recover energy from digestion gas, etc. The digested sludge generated in the digestion equipment is dehydrated in a dehydrator, but the digestion dehydration filtrate discharged during this process contains high concentrations of nitrogen and phosphorus. The digestion dehydration filtrate is generally returned to the water treatment process as return water, so there was a problem that the nitrogen and phosphorus continued to circulate within the treatment system, placing an excessive load on the existing water treatment equipment. The nitrogen and phosphorus that could not be completely removed were discharged into rivers and other watercourses together with the treated water, causing a deterioration in the quality of the discharged water and causing eutrophication.

[0008] In Patent Document 1, when dehydrating mixed raw sludge after digestion in a digester, organic matter (fibrous matter) extracted from the raw sludge is added to improve the dehydration of the sludge, but this is a technique in which organic matter (fibrous matter) generated within one treatment system is added to the digested sludge, and it is not a technology that combines multiple treatment systems. Also, when organic matter (fibrous matter) is collected in the upstream stage of the digester, the amount of organic matter (fibrous matter) put into the digester is reduced, which affects the digestion efficiency and reduces the amount of digestion gas generated.

[0009] Patent Document 2 also discloses a technology for subjecting sewage return water generated after digestion (digestion dewatered filtrate) to contact stabilization treatment to adsorb and remove organic matter, nitrogen, and phosphorus, and a technology for treating digested sludge generated from two treatment systems together, but the two treatment systems use sludge treatment systems with the same flow, not sludge treatment systems with different flows. In other words, there was no technology for transferring sewage return water generated at one treatment plant of sludge treatment systems with different flows to the other treatment plant and subjecting it to contact stabilization treatment.

[0010] The present invention provides a sludge treatment system that integrates two different systems, an undigested treatment system that treats easily dewaterable sludge and a digestion treatment system that treats difficult to dewaterable sludge, and is characterized in that fibrous material recovered from the easily dewaterable sludge is supplied to the difficult to dewaterable sludge, and the digested and dehydrated filtrate of the difficult to dewaterable sludge is transported to the treatment system for the easily dewaterable sludge for contact stabilization treatment. [Means for solving the problem]

[0011] The present invention relates to In a sludge treatment system including a first treatment system for dehydrating easily dewaterable sludge, which includes primary sludge that has been gravity-settled in a primary settling tank and excess sludge that has been gravity-settled in a final settling tank, in a dehydrator without digestion, and a second treatment system for dehydrating difficult-to-dewaterable sludge, which is generated by digesting the primary sludge that has been gravity-settled in the primary settling tank and the excess sludge that has been gravity-settled in the final settling tank, in a dehydrator, fibrous matter is recovered from a recovery device installed downstream of the primary settling tank in the first treatment system, and the recovered fibrous matter is added to the difficult-to-dewaterable sludge between the digestion tank and the dehydrator in the second treatment system for dehydration, and the digested and dehydrated filtrate discharged from the dehydrator in the second treatment system is transferred to a contact tank installed downstream of the final settling tank in the first treatment system, and the digested and dehydrated filtrate is supplied from the final settling tank. By contacting excess sludge with the sludge and subjecting it to contact stabilization treatment, the dewaterability of the difficult-to-dewater sludge can be improved, and the nitrogen and soluble phosphorus resulting from SS in the digested and dewatered filtrate can be adsorbed onto the excess sludge and removed, thereby reducing the concentrations of nitrogen and phosphorus in the digested and dewatered filtrate.

[0013] The contact stabilization treatment is carried out on a mixture of excess sludge and digested dewatered filtrate. First treatment system Anaerobic and aerobic treatment is carried out in the contact tank (6), and the nitrogen and phosphorus in the digested and dehydrated filtrate are adsorbed onto the excess sludge, thereby purifying the digested and dehydrated filtrate. Effect of the Invention

[0014] The sludge treatment system of the present invention adds fibrous material recovered from the primary sludge generated in the treatment system for easily dewaterable sludge to the difficult-to-dewaterable sludge in a different treatment system, thereby improving the dewaterability of the difficult-to-dewaterable sludge. This allows the production of a dewatered cake with a low moisture content, making it possible to minimize the energy used in the subsequent incineration process. In addition, the digested dewatered filtrate generated in the treatment system for difficult-to-dewaterable sludge is transferred to the contact tank of the treatment system for easily dewaterable sludge, where nitrogen and soluble phosphorus originating from SS in the digested dewatered filtrate are brought into contact with excess sludge and adsorbed and removed, thereby reducing the load imposed on the water treatment facility by the digested dewatered filtrate. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a flow diagram of a system according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] FIG. 1 is a flow diagram of a system according to the present invention. The first treatment system is a treatment flow for easily dewaterable sludge, and in this embodiment, it includes a primary sedimentation tank 1A where water to be treated containing fibrous matter is subjected to gravity settling, a gravity thickening tank 2A ​​where the primary sludge separated in the primary sedimentation tank 1A is thickened, a recovery device 3 where a predetermined amount of primary sludge is extracted from the gravity thickening tank 2A ​​to selectively separate and recover fibrous matter, a reaction tank 4A where organic matter contained in the primary treated water supplied from the primary sedimentation tank 1A is decomposed by biological treatment, and the treated water supplied from the reaction tank 4A is subjected to gravity settling. It consists of a final settling tank 5A, which allows settling to occur and the supernatant water is disinfected before being discharged into a river or the like; a contact tank 6 which removes nitrogen and phosphorus which are substances that cause eutrophication; a mechanical thickener 7A which mechanically thickens the excess sludge withdrawn from the contact tank 6; a sludge storage tank 8 which temporarily stores the mechanically thickened excess sludge and the gravity thickened sludge withdrawn from the gravity thickening tank 2A; a flocculation mixing tank 9A which supplies a flocculant to the mixed raw sludge produced in the sludge storage tank 8; and a dewatering device 10A which dewaters the flocculated sludge.

[0017] The flocculated sludge dewatered in the dewatering device 10A has good dewaterability because it contains a large amount of fibrous matter derived from the primary sludge, and the flocculated sludge in the first treatment system can be said to be easily dewaterable sludge.

[0018] The second treatment system is a treatment flow for difficult-to-dewater sludge, and in this embodiment, it consists of a primary sedimentation tank 1B, which allows the water to be treated to settle by gravity, a reaction tank 4B, which uses biological treatment to decompose organic matter contained in the primary treated water supplied from the primary sedimentation tank 1B, a final sedimentation tank 5B, which allows the treated water supplied from the reaction tank 4B to settle by gravity, disinfects the supernatant water, and then discharges it, a thickening tank 2B, which thickens the primary settled sludge separated in the primary sedimentation tank 1B, a mechanical thickener 7B, which mechanically thickens the excess sludge extracted in the final sedimentation tank 5B, a digestion tank 11, which anaerobically treats the thickened sludge, a flocculation mixing tank 9B, which supplies a flocculant to the digested sludge that has been digested, and a dewatering device 10B, which dewaters the flocculated sludge produced by flocculating the digested sludge.

[0019] The flocculated sludge dewatered in the dewatering device 10B is based on digested sludge that has been anaerobically treated in the preceding digestion tank 11, so only a small amount of fibrous material remains in the sludge. In addition, the digestion process leaves behind a large amount of fine colloidal particles that adversely affect the filtration speed of a filtration-type dewatering machine. As a result, the dewatering is extremely poor, and the flocculated sludge in the second treatment system can be said to be difficult to dewater.

[0020] The digested sludge in the second treatment system is added with fibrous material transferred from the recovery device 3 in the first treatment system as a dewatering aid. It is preferable to add the fibrous material to the digested sludge between the digester 11 and the coagulation / mixing tank 9B, or to the digested sludge supplied to the coagulation / mixing tank 9B, at a stage prior to dewatering.

[0021] Since the coagulated sludge that is separated into solid and liquid in the dehydrator 10B of the second treatment system is based on digested sludge, the digested and dehydrated filtrate contains SS, nitrogen due to SS, and dissolved phosphorus. To remove these, the digested and dehydrated filtrate is transferred to the contact tank 6 of the first treatment system. In the contact tank 6, the SS, nitrogen due to SS, and dissolved phosphorus in the digested and dehydrated filtrate are adsorbed by the excess sludge extracted from the final settling tank 5A, and then dehydrated and discharged from the first treatment system with these incorporated in the solid matter (dehydrated cake).

[0022] The excess sludge just removed from the final settling tank 5B has been biologically treated in the reaction tank 4B and functions as activated sludge, so it efficiently adsorbs SS, nitrogen resulting from SS, and dissolved phosphorus in the digested and dehydrated filtrate transferred to the contact tank 6. In addition, the digested and dehydrated filtrate purified in the contact tank 6 can be reused in the water treatment process.

[0023] In this embodiment, the primary sludge and excess sludge of the first treatment system are supplied to the sludge storage tank 8 to produce mixed raw sludge, which is then subjected to solid-liquid separation in the dewatering device 10A. 10 In this case, a part of the fibrous material recovered from the primary sludge is added to the excess sludge as a dewatering aid.

[0024] Alternatively, the primary sludge in the first treatment system may be transferred to the thickening tank 2B in the second treatment system. In this case, the excess sludge extracted from the final settling tank 5A in the first treatment system is added with a portion of the fibrous material recovered from the primary sludge as a dewatering aid, and is subjected to solid-liquid separation treatment alone in the dewatering device 10A.

[0025] When treatment systems for both easily dewaterable sludge and difficult to dewaterable sludge are mixed within the same treatment plant, the transferred materials such as fibrous materials and digested dewatered filtrate are transported to each treatment system through connecting pipes.

[0026] On the other hand, when the treatment systems for easily dewaterable sludge and difficult to dewaterable sludge are located in different treatment plants, the transferred materials such as fibrous materials and digested dewatered filtrate are transported to the respective treatment systems via connecting pipes.

[0027] In this embodiment, two different treatment systems have been described in detail, but for example, if there are two treatment systems for easy-to-dewaterable sludge and one treatment system for difficult-to-dewaterable sludge, fibrous material may be extracted from each of the two treatment systems for easy-to-dewaterable sludge and transported to one treatment system for difficult-to-dewaterable sludge. EXAMPLES

[0028] <Primary Sedimentation Tank> The water to be treated flows into the primary sedimentation tank 1A of the first treatment system. The primary sludge contains 40% to 60% fibrous material in terms of solid content. The supernatant water from the primary sedimentation tank 1A is supplied to the reaction tank 4A, and the settled primary sludge is extracted and supplied to the gravity thickening tank 2A. Depending on the size of the treatment plant, the water to be treated is retained in the primary sedimentation tank 1 for 1 to 2 hours.

[0029] <Gravity concentration tank> Next, in the gravity thickening tank 2A, the primary sludge is thickened by gravity. The thickened primary sludge is supplied to the sludge storage tank 8, and a predetermined amount of primary sludge is withdrawn from the gravity thickening tank 2A ​​and supplied to the recovery device 3. The gravity thickening tank 2A ​​also thickens the residues, such as decomposable organic matter, returned from the recovery device 3.

[0030] <Collection device> Next, in the recovery device 3, fibrous matter is separated and recovered from the primary sludge extracted from the gravity thickening tank 2A. Here, the primary sludge contains a large amount of fibrous matter. It has been found that the majority of the fibrous matter is fibrous matter derived from toilet paper, with a fiber length of 0.1 mm to 0.5 mm and a fiber diameter of 1 μm to 50 μm. As the recovery device 3 for fibrous matter, a known method can be used in which sludge is supplied to a cylindrical screen equipped with a helical screw blade, and separated and recovered by the screen while being transported inside.

[0031] In addition to toilet paper-derived fibrous materials, fibrous materials contained in the water to be treated also include plant-derived fibrous materials and food waste-derived fibrous materials, which function as dewatering aids if they are broken down into fibers. The shape of the recovered fibrous materials may be uniformed by grinding the sludge in the recovery device 3 or in the stage preceding the recovery device 3. The recovered fibrous materials are transferred to the stage preceding the dewatering device 10B in the second treatment system to be used as dewatering aids for the difficult-to-dewater sludge before dewatering in the second treatment system. Residues other than the fibrous materials are returned to the primary sedimentation tank 1A or the gravity thickening tank 2A. In this embodiment, the fibrous materials are recovered from the sludge thickened in the gravity thickening tank 2A, but the fibrous materials may be recovered directly from the primary sedimentation tank 1A. If necessary, the fibrous materials may be added to the sludge in the first treatment system.

[0032] <Reaction tank> Next, in the reaction tank 4A, activated sludge (sludge containing a large amount of aerobic microorganisms) is added to the primary treated water supplied from the primary settling tank 1A, and air is blown in and agitated. The air (oxygen) and the organic matter in the primary treated water cause the microorganisms in the activated sludge to grow, reducing the organic matter (dirt) in the primary treated water and causing the activated sludge to form flocs, making it easier to settle and flowing out to the next stage. Depending on the size of the treatment plant, the primary treated water is retained in the reaction tank 4 for 6 to 10 hours.

[0033] <Final Sedimentation Tank> Next, in the final settling tank 5A, the treated water mixed with activated sludge supplied from the reaction tank 4A is retained and gravity settling takes place. The supernatant water from the final settling tank 5A is disinfected and then discharged into a river or the like. The settled sludge that settles to the bottom of the final settling tank 5A is returned from the final settling tank 5A to the reaction tank 4A. The part of the sludge that has grown in the microorganisms is discharged as excess sludge into the contact tank 6. This excess sludge is made up of polysaccharides, proteins, and nucleic acids secreted by the microorganisms, and is known to have extremely poor dewaterability. Depending on the size of the treatment plant, the treated water is retained in the final settling tank 5 for 3 to 4 hours.

[0034] <Contact tank> Next, in the contact tank 6, the excess sludge supplied from the final settling tank 5A and the digested dewatered filtrate transferred from the second treatment system are mixed. The supplied digested dewatered filtrate comes into contact with the excess sludge in the contact tank 6 and undergoes contact stabilization treatment. After the contact stabilization treatment in which phosphorus is incorporated into microorganisms in the sludge is performed in the anaerobic tank and aerobic tank constituting the contact tank 6, the phosphorus incorporated into the microorganisms is extracted as excess sludge, so that phosphorus can be removed. An example of the contact tank 6 is a phosphorus removal method using a known anaerobic-aerobic method (AO method). Unlike the reaction tank 4B in which sludge is retained for a long time to perform biological treatment, the contact tank 6 retains sludge for a shorter time than the treatment performed in the reaction tank 4B, for example, 30 minutes to 1 hour depending on the design, and contacts phosphorus with the sludge to adsorb and remove phosphorus. In addition, the SS in the digested dewatered filtrate is adsorbed by the excess sludge in the contact tank 6, so that the nitrogen content caused by the SS is adsorbed and removed. However, the soluble nitrogen cannot be removed in a short time and is sent back to the first treatment system as return water, where it reacts with tank It is treated at 4A and then released.

[0035] <Mechanical concentrator> Next, in the mechanical thickener 7A, the excess sludge extracted from the contact tank 6 is mechanically thickened and then supplied to the sludge storage tank 8. At this time, the separated liquid obtained by solid-liquid separation is returned to the primary sedimentation tank 1A.

[0036] <Sludge storage tank> Next, the primary sludge and excess sludge are temporarily stored in the sludge storage tank 8 to produce mixed raw sludge (easily dewaterable sludge). By mixing the primary sludge, which has good dewaterability, with the excess sludge, which has poor dewaterability, the fibrous material contained in the primary sludge is uniformly dispersed, allowing the fibrous material to function as nuclei for flocculation and forming water channels during dewatering. The produced mixed raw sludge is transferred to the flocculation mixing tank 9A.

[0037] <Agglomeration mixing tank> Next, in the coagulation mixing tank 9A, the mixed raw sludge supplied from the sludge storage tank 8 and the coagulant supplied from a coagulant supply device (not shown) are mixed while being uniformly stirred, to form coagulated sludge that can be stably dewatered in the dewatering device 10A.

[0038] <Dehydration equipment> Next, in the dewatering device 10A, the flocculated sludge supplied from the flocculation mixing tank 9A is dewatered to produce a dewatered cake with a stable low moisture content. The dewatered cake contains a large amount of phosphorus that was captured during the contact stabilization treatment in the contact tank 6, and can be effectively used as a nutrient component for compost. The dewatered filtrate after solid-liquid separation is returned to the primary settling tank 1A.

[0039] Components similar to those of the first processing system are omitted. <Mechanical concentrator> In the mechanical thickener 7B, the excess sludge separated in the final settling tank 5B is thickened by mechanical action. The thickened mechanically thickened sludge is supplied to the digester 11. Note that the primary settling sludge (gravity thickened sludge, if a gravity thickener tank 2B is provided) is also supplied to the digester tank 11, but the mechanically thickened sludge is fed to the digester tank 11 separately from the primary settling sludge (gravity thickened sludge). 11 The separated liquid after solid-liquid separation is returned to the initial settling tank 1B.

[0040] <Digestion tank> In the digester 11, the organic matter in the sludge is decomposed by anaerobic microorganisms into organic acids, carbon dioxide, etc. The organic acids are further decomposed by the anaerobic microorganisms into methane and hydrogen sulfide. Once decomposition is complete and the digested sludge is stable, its weight is reduced to about 50-60% of that before the digestion process. The digestion gas generated in the digestion process can be used as energy for boilers, incineration facilities, generators, etc.

[0041] <Agglomeration mixing tank> Next, in the flocculation mixing tank 9B, the digested sludge supplied from the digester tank 11, the flocculant supplied from a flocculant supplying device (not shown), and the fibrous material supplied from the first treatment system are mixed while being uniformly stirred to form flocculated sludge that can be stably dewatered in the dewatering device 10B. At this time, by supplying the fibrous material extracted from the first treatment system to the flocculated sludge, it is possible to cause it to function as nuclei for flocculation, making it possible to perform flocculation with the minimum amount of flocculant required.

[0042] <Dehydration equipment> Next, in the dewatering device 10B, the flocculated sludge supplied from the flocculation mixing tank 9B is dewatered to produce a dewatered cake with a stable low moisture content. The discharged digested and dehydrated filtrate is transferred to the contact tank 6 of the first treatment system. [Industrial Applicability]

[0043] The sludge treatment system of the present invention is an integrated system that treats easily dewaterable sludge and digestion treatment system that treats difficult-to-dewaterable sludge, and can utilize the advantages of different sewage treatment systems to compensate for their disadvantages. By linking multiple treatment plants, it is also possible to form a wide-area treatment system. [Explanation of symbols]

[0044] 1 Primary sedimentation tank 5 Final Sedimentation Tank 6 Contact tank

Claims

1. A first treatment system in which easily dewaterable sludge, which includes primary sludge sedimented by gravity in a primary sedimentation tank (1A) and excess sludge sedimented by gravity in a final sedimentation tank (5A), is dewatered in a dewatering device (10A) without being digested; A sludge treatment system including a second treatment system for dehydrating the difficult-to-dehydrate sludge produced by digesting the primary sludge that has been gravity-settled in the primary sedimentation tank (1B) and the excess sludge that has been gravity-settled in the final sedimentation tank (5B), Fibrous material is recovered from a recovery device (3) installed downstream of a primary sedimentation tank (1A) in a first treatment system, and the recovered fibrous material is added to difficult-to-dewater sludge between a digestion tank (11) and a dewatering device (10B) in a second treatment system for dewatering. The digested and dehydrated filtrate discharged from the dehydrator (10B) of the second treatment system is transferred to a contact tank (6) installed downstream of the final settling tank (5A) of the first treatment system, and is brought into contact with excess sludge supplied from the final settling tank (5A) for contact stabilization treatment. A sludge treatment system comprising:

2. The contact stabilization treatment is a treatment in which anaerobic and aerobic treatment are carried out in a contact tank (6) of the first treatment system where the excess sludge and the digested and dehydrated filtrate are mixed, and nitrogen and phosphorus in the digested and dehydrated filtrate are adsorbed by the excess sludge.

2. The sludge treatment system according to claim 1 .

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