Sludge property prediction method and sludge property constant control method

Abstract

To provide a sludge property prediction method and a sludge property constant control method that improve dewatering treatment efficiency by predicting the properties of consolidated sludge based on the properties and transfer volume of each local sludge, and by controlling the transfer volume of each local sludge to produce consolidated sludge with uniform properties.SOLUTION: In a sludge treatment system where local sludge transported from multiple local treatment plants is mixed in a consolidated sludge tank installed at a consolidated treatment plant and then dewatered, sludge property reference values serving as indicators for determining sludge properties are set in advance. The measured sludge property values of each local sludge are compared with the sludge property reference values to determine each sludge property. By predicting the sludge properties of the consolidated sludge generated within the consolidated sludge tank based on the transfer ratio of each local sludge, it is possible to produce consolidated sludge with consistent properties from multiple local sludges with different sludge properties, thereby improving dewatering efficiency.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a sludge property prediction method and a sludge property constant control method for predicting the sludge properties of aggregated sludge aggregated from a plurality of local treatment plants and controlling the amount of transfer from each treatment plant so that the sludge properties of the aggregated sludge are constant. [Background technology]

[0002] Conventionally, sludge treatment in urban areas has been carried out by collecting sludge from multiple local treatment plants using sludge transport means such as sludge pipes and trucks, rather than having sludge treatment equipment at each individual sewage treatment plant, and then treating the sludge all at once at a centralized treatment plant.

[0003] For example, Patent Document 1 discloses a technology for transporting sludge and fibrous material separately from multiple local treatment plants to a centralized treatment plant for centralized treatment, and describes that if the fibrous material concentration of the centralized sludge transported to the centralized treatment plant is lower than a predetermined value, the centralized fibrous material is supplied to improve the dewaterability of the sludge.

[0004] In addition, in a typical sludge treatment system at a sewage treatment plant, as shown in Figure 3 of the present application, primary sludge extracted from a primary settling tank is thickened in a gravity thickener, and excess sludge generated in a final settling tank is thickened in a mechanical thickener, and the two are mixed in a sludge storage tank and then dehydrated in a dehydrator. However, a method is also known in which the gravity thickener and mechanical thickener are omitted and the primary sludge and excess sludge are directly dehydrated in an unthickened state. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6298792 Summary of the Invention [Problem to be solved by the invention]

[0006] In the past, sludge transported from multiple local treatment plants varied in concentration and properties, and the properties of the sludge could change dramatically during transport, making it difficult to consistently produce dehydrated cake with a low moisture content at a centralized treatment plant.

[0007] Patent Document 1 describes a technology that can prevent the decay of fibrous material by transporting sludge and fibrous material separately from each local treatment plant to a centralized treatment plant, but it requires the installation of new pipes and pressure pumps for individual transport, which increases the labor and cost of transportation.In addition, the technology measures the fibrous material concentration of centralized sludge transported to the centralized treatment plant to improve the dewaterability of the sludge, and controls the amount of fibrous material supplied according to the concentration, but there is no description or suggestion of using an indicator other than fibrous material for control.

[0008] Furthermore, when a sludge treatment system that directly dehydrates the primary sludge extracted from the primary sedimentation tank and the excess sludge generated in the final sedimentation tank in an unconcentrated state is applied to a centralized treatment plant, mixed sludge, which is a mixture of unconcentrated primary sludge and excess sludge, is transported from each local treatment plant to the centralized treatment plant.However, the properties of the mixed sludge vary from treatment plant to treatment plant, and since mixed sludge with different sludge properties is treated centrally, there is a problem that the dehydration performance of the dehydrators operating at the centralized treatment plant is not stable.

[0009] The present invention has been made in consideration of the above-mentioned problems, and provides a sludge property prediction method and a sludge property constant control method that determine the sludge properties of each local sludge transported from a plurality of local treatment plants, predict the sludge properties of the consolidated sludge from the transport rate of each local sludge, and control the transport amount of each local sludge to keep the sludge properties of the consolidated sludge constant, thereby making it possible to dehydrate consolidated sludge with constant sludge properties, thereby improving dehydration efficiency and enabling the stable production of dehydrated sludge with a low moisture content. [Means for solving the problem]

[0010] The present invention is a sludge treatment system in which local sludge transported from multiple local treatment plants is mixed in a centralized sludge tank installed at a centralized treatment plant and then dewatered.A sludge property standard value that serves as an indicator for discriminating sludge properties is set in advance, and the sludge property measurement values ​​of each local sludge are compared with the sludge property standard value to determine each sludge property.After that, the sludge properties of the centralized sludge generated in the centralized sludge tank are predicted based on the transfer ratio of each local sludge, thereby enabling efficient centralized treatment of multiple local sludges with different sludge properties.

[0011] By controlling the rate at which the local sludge is transferred so that the sludge property values ​​of the consolidated sludge meet the sludge property standard values, consolidated sludge with uniform sludge properties can be produced. [Effects of the Invention]

[0012] The sludge property prediction method and sludge property constant control method according to the present invention can predict the sludge properties of the aggregated sludge from the sludge transport rates of multiple local sludges whose sludge properties have been determined. Furthermore, by controlling the transport rate of each local sludge based on the sludge property measurements in the aggregated sludge tank, the sludge properties of the generated aggregated sludge can be made uniform. Because aggregated sludge with uniform sludge properties can be dehydrated in a downstream dehydrator, dehydration efficiency is improved, and dehydrated sludge with a low moisture content can be stably obtained. This also leads to improved operational efficiency and reduced disposal costs of downstream facilities that dispose of the dehydrated sludge. Furthermore, the methods can be applied to existing treatment plants without the need for additional piping, pumps, etc. Furthermore, local sludge is produced by mixing unconcentrated primary sludge and excess sludge, and since the thickening equipment for thickening the primary sludge and excess sludge is omitted, the retention time of the sludge until dewatering is shortened, suppressing the decay of the sludge, and also reducing the installation area, initial costs, running costs, etc., thereby suppressing carbon dioxide emissions. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a schematic configuration diagram of a sludge treatment system according to the present invention. [Figure 2] FIG. [Figure 3] FIG. 1 is a flow chart of a conventional sludge treatment method. DETAILED DESCRIPTION OF THE INVENTION

[0014] FIG. 1 is a schematic diagram of a sludge treatment system according to the present invention. The sludge treatment system according to this embodiment is composed of a plurality of local treatment plants 1 and a centralized treatment plant 2, and sludge transported from each local treatment plant 1 is centrally treated at the centralized treatment plant 2. The number of local treatment plants can be selected as appropriate, but as an example, this embodiment is configured such that local sludge A to D generated at four local treatment plants 1A to 1D are centrally treated at the centralized treatment plant 2. Note that the treatment method at each local treatment plant 1 is the same, so below, the treatment method at local treatment plant 1A will be described in detail, and the treatment methods at local treatment plants 1B to 1D will be omitted.

[0015] The local treatment plant 1A consists of a primary sedimentation tank 3 which sediments and separates the water to be treated that flows into the sewage treatment plant, a reaction tank 4 which biologically treats the primary treated water supplied from the primary sedimentation tank 3 by injecting oxygen into it, a final sedimentation tank 5 which sediments and separates the secondary treated water supplied from the reaction tank 4 and disinfects the supernatant water before discharging it into a river or the like, and a local sludge tank 6 which mixes the primary sludge sedimented in the primary sedimentation tank 3 with the excess sludge sedimented in the final sedimentation tank 5. Because no thickening equipment is installed downstream of the primary sedimentation tank 3 or the final sedimentation tank 5, the primary sludge and excess sludge are transferred to the local sludge tank 6 in an unthickened state.

[0016] In the local sludge tank 6, unconcentrated primary sludge and excess sludge are mixed, and the resulting unconcentrated local sludge A is temporarily stored. The local sludge tank 6 is a mixed sludge storage tank, and as an example, a stirring means (not shown) with stirring blades is installed inside the tank. By periodically stirring the primary sludge and excess sludge, a uniformly mixed mixed sludge (local sludge A) is generated.

[0017] The local sludge tank 6 is equipped with a measuring unit 9 that measures the sludge properties of the local sludge A in the tank, and can measure the sludge properties of each local sludge transported to the centralized treatment plant 2. The local sludge A generated in the local sludge tank 6 is transported to the centralized treatment plant 2 through a sludge transfer pipe 8 equipped with a pressure pump 7. Note that the measuring unit 9 may be installed in the sludge transfer pipe 8 to measure the sludge properties of the local sludge A. Furthermore, the means for transporting the local sludge A is not limited to the sludge transfer pipe 8, and a vehicle such as a truck may also be used.

[0018] The centralized treatment plant 2 is composed of a centralized sludge tank 10 connected to one end of a sludge transfer pipe 8, the other end of which is connected to a local sludge tank 6, a flocculation and mixing tank 11 that flocculates the centralized sludge produced in the centralized sludge tank 10 to produce flocculated sludge, and a dehydrator 12 that separates the flocculated sludge produced in the flocculation and mixing tank 11 into solid-liquid separation to produce dewatered sludge.

[0019] The concentrated sludge tank 10 is supplied with unconcentrated local sludge A to D transferred from the local sludge tank 6. The concentrated sludge tank 10 is composed of an adjustment tank 10A that mixes and agitates multiple local sludges, and a sludge storage tank 10C that temporarily stores the concentrated sludge mixed and agitated in the adjustment tank 10A. A mixing tank 10B may be provided between the adjustment tank 10A and the sludge storage tank 10C. Each tank is provided with a known agitation means, but the shape of each tank is not limited. Furthermore, the concentrated sludge tank 10 may not be composed of multiple tanks, but may be composed of a single tank that can mix and store sludge. A spare tank (not shown) may be provided upstream of the concentrated sludge tank 10 to receive sludge overflowing from the local sludge tank 6.

[0020] In the flocculation mixing tank 11, a flocculant is supplied from a flocculant supply device (not shown) to the concentrated sludge produced in the concentrated sludge tank 10, and the flocculant is mixed and stirred to produce flocculated sludge consisting of strong flocs.

[0021] The dehydrator 12 is a screw press that thickens and dehydrates the flocculated sludge, and in this embodiment, a known screw press is used in which a thickening section is placed above a dehydration section (not shown). Each of the thickening section and the dehydration section has a rotatable screw shaft with screw blades attached therearound inside an external cylindrical screen, and the supplied sludge is transported by the screw blades toward the terminal end, where it is subjected to solid-liquid separation, producing dehydrated sludge.

[0022] In this embodiment, the primary sludge separated from the primary settling tank 3 and the excess sludge separated from the final settling tank 5 are transferred to the local sludge tank 6 without being thickened, so a screw press having a thickening section at its top that can produce thickened sludge with high efficiency is used, but the type of screw press is not limited to this. Furthermore, the dehydrator is not limited to a screw press, and may be any of a belt press, centrifugal dehydrator, pressure dehydrator, vacuum dehydrator, etc.

[0023] FIG. 2 is a flow chart of the operation control method according to the present invention. In this embodiment, local sludge A to D are transported from four local treatment plants 1A to 1D to a centralized treatment plant 2 for centralized treatment. Measuring units 9A to 9D are provided in each of the local sludge tanks 6A to 6D installed in the four local treatment plants 1A to 1D. Each measuring unit 9 is a nitrogen meter and can measure the nitrogen content of each local sludge A to D. In this embodiment, the standard Kjeldahl method is used to calculate the crude protein amount by multiplying the measured nitrogen content by a coefficient of 6.25, and the sludge properties are determined based on the calculated crude protein amount. Note that the method for calculating the crude protein amount is not limited to this.

[0024] Crude protein content is used as an indicator for determining sludge properties, but other sludge property items such as pH, M alkalinity, SS (suspended solids), TS (total evaporated residue), dissolved constituent concentration, VTS (loss on ignition), VSS (volatile organic matter), electrical conductivity, anionic degree, fibrous matter (100 mesh / 200 mesh), crude fiber, crude suspended matter, sand content, ORP (oxidation-reduction potential), data potential, chloride ion concentration, and total iron can also be measured to determine sludge properties.

[0025] Valves VA-VD are installed in sludge transfer pipes 8A-8D installed between each of the local sludge tanks 6A-6D and the centralized sludge tank 10, and the amount of local sludge A-D transferred can be adjusted by changing the aperture of each valve V. Since the sludge properties of each local sludge can be determined based on the values ​​measured by each measuring unit 9, for example, if the sludge properties of local sludge A stored in local sludge tank 6A are determined to be good, the aperture of valve VA can be increased to increase the proportion transferred from local sludge tank 6A. Conversely, if the sludge properties of local sludge B stored in local sludge tank 6B are determined to be poor, the aperture of valve VB can be decreased to decrease the proportion transferred from local sludge tank 6B. Note that a pressure pump 7 and a flow meter (not shown) may be installed instead of valve V to transfer a predetermined amount at a time; the sludge transfer method is not limited to this.

[0026] The measuring units 9A-9D and the valves VA-VD are connected to the control device 13, and the sludge property measurement values ​​of the local sludge A-D measured by the measuring units 9A-9D are transmitted to the control device 13. The transmitted sludge property measurement values ​​of the local sludge are compared with preset sludge property reference values ​​(described later) to determine whether the sludge properties are good or bad. Then, the sludge transfer amount for each local sludge is set based on the sludge properties of each local sludge, and each local sludge is transferred to the consolidated sludge tank 10 in a predetermined proportion.

[0027] The concentrated sludge tank 10 is also provided with a measuring unit 9E, which is a device similar to the measuring units 9A to 9D, and is configured to be able to determine the amount of crude protein from the nitrogen content in the concentrated sludge tank 10. The measuring unit 9E is also connected to the control device 13, and is configured to transmit the sludge property values ​​of the concentrated sludge in the concentrated sludge tank 10 to the control device 13. [Example]

[0028] The sludge property prediction method and the sludge property constant control method according to this embodiment will be described in detail below with reference to FIG. A. Initial Setup A sludge property reference value is set in advance as a sludge property discrimination index for the local sludge in each local sludge tank 6 and the aggregated sludge in the aggregated sludge tank 10. In this embodiment, the sludge property reference value for the local sludge and the aggregated sludge is the crude protein content with a predetermined range. The sludge property reference value may be set to the same numerical range for the local sludge and the aggregated sludge, or different numerical ranges may be set. Furthermore, appropriate modifications can be made, such as using one as an index different from the crude protein content.

[0029] B. Measurement of local sludge properties The properties of the local sludge generated in each of the local treatment plants 1A to 1D are measured. The properties of the local sludge are measured using measuring units 9A to 9D installed in each local sludge tank 6. Measuring unit 9 is a nitrogen meter, and the nitrogen meter measures the nitrogen content of the local sludge stored in the local sludge tank 6. Then, using the standard Kjeldahl method, the measured nitrogen content is multiplied by a coefficient of 6.25 to calculate the crude protein content of each local sludge.

[0030] C. Sludge characterization of local sludge The calculated crude protein amount (sludge property measurement value) is sent to the control device 13 and compared with a predetermined sludge property standard value. If the sludge property measurement value is within the range of the sludge property standard value, the sludge property is determined to be good, and on the other hand, if the sludge property measurement value is outside the range of the sludge property standard value, the sludge property is determined to be poor. Since the crude protein amount is an index that can determine sludge property, the quality of sludge property can be determined by understanding the crude protein amount contained in each local sludge.

[0031] D. Method for predicting sludge properties of concentrated sludge Based on the determined sludge properties of each local sludge, the transfer ratios of the local sludge with good sludge properties and the local sludge with poor sludge properties are set, respectively.The sludge properties of the consolidated sludge generated in the consolidated sludge tank 10 are then predicted based on the transfer ratios of the sludge with good sludge properties and the sludge with poor sludge properties.

[0032] E. Method for controlling the sludge properties of concentrated sludge In this embodiment, the sludge transfer rate of each local sludge is controlled to maintain constant sludge property values ​​in the centralized sludge tank 10. Because the sludge properties of each local sludge are determined, controlling the transfer rate of sludge with good or poor sludge properties allows for the production of centralized sludge with consistent sludge properties. The centralized sludge tank 10 is equipped with a measuring unit 9E capable of measuring nitrogen content. If the sludge property measurement value (crude protein content) meets the sludge property standard value, the sludge transfer continues at the current transfer rate. On the other hand, if the sludge property measurement value does not meet the sludge property standard value, the valve V is changed to change the local sludge transfer rate. The value measured by the measuring unit 9E is transmitted to the control device 13, which then sends a command to adjust the valve V based on the measured value. Each valve V is set to a minimum opening, so that a minimum amount of sludge is always transferred, even if the sludge property is poor. Therefore, it is possible to prevent sludge with poor sludge properties from being stored in the local sludge tank 6 for a long period of time, which would otherwise cause the sludge to decay.

[0033] Furthermore, although the method for adjusting the opening of each valve V is not particularly limited, it may be a control method in which the opening is gradually increased or decreased by a predetermined amount in accordance with the measured sludge property measurement value, and by gradually controlling the opening according to the measurement value, the sludge property value of the aggregated sludge can be efficiently kept within the desired range.

[0034] By using the control method of this embodiment, even when multiple local sludges with different sludge properties flow in, it is possible to constantly transfer an optimal amount to the concentrated sludge tank 10, making it possible to produce concentrated sludge with uniform sludge properties in the concentration tank 10. This makes it possible to produce flocculated sludge with high flocculation strength in the downstream flocculation mixing tank 11 and reduce the amount of flocculant supply. Furthermore, since flocculated sludge with uniform sludge properties can be supplied to the downstream dehydrator 12, dehydration performance is improved and dehydrated sludge with a low moisture content can be stably obtained. It is possible to increase the flocculation treatment efficiency and dehydration efficiency, improving the treatment efficiency of the entire facility.

[0035] In this embodiment, the primary sludge separated in the primary sedimentation tank 3 and the excess sludge separated in the final sedimentation tank 5 are mixed in an unconcentrated state without being concentrated, and the resulting local sludge (mixed raw sludge) is subjected to centralized treatment. However, the present invention may also be applied to a treatment method in which the primary sludge and excess sludge are separately concentrated, and then mixed to produce local sludge for centralized treatment. Furthermore, the present invention is not limited to the conventional activated sludge method, and may also be applied to other treatment methods such as the oxidation ditch method. It goes without saying that the sludge to be treated is not limited to mixed raw sludge. Furthermore, although the four local treatment plants described in detail in this embodiment use the same treatment method, the present invention may also be applied to a centralized treatment of local sludge transported from multiple local treatment plants using different treatment methods.

[0036] The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. [Industrial Applicability]

[0037] The sludge property prediction method and sludge property constant control method of the present invention can produce consolidated sludge with consistent sludge properties even when treating multiple local sludges with different sludge properties, thereby improving the efficiency of subsequent dewatering treatment. As a result, high-quality dewatered sludge with a low moisture content is produced, reducing the cost of dewatered sludge disposal, such as landfilling, incineration, and composting. The incineration treatment time is also reduced, reducing carbon dioxide emissions and making this an environmentally friendly technology. [Explanation of symbols]

[0038] 1 Local treatment plant 2. Centralized treatment plant 3 Primary sedimentation tank 5 Final settling tank 10. Concentrated sludge tank

Claims

1. A sludge treatment system in which local sludge transported from a plurality of local treatment plants (1) is mixed in a centralized sludge tank (10) installed in a centralized treatment plant (2) and then dehydrated, A sludge property standard value that serves as a discrimination index for sludge properties is set in advance, The measured sludge properties of each local sludge are compared with the sludge property standard values ​​to determine the sludge properties. Based on the transfer rate of each local sludge, the sludge properties of the aggregated sludge generated in the aggregated sludge tank (10) are predicted. A method for predicting sludge properties.

2. The transfer rate of the local sludge is controlled so that the sludge property value of the aggregated sludge meets the sludge property standard value.

2. The method for controlling sludge properties to a constant state according to claim 1.

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