Sludge treatment system and sludge treatment method

Abstract

To provide more effective utilization of digest gas in a sludge treatment system.SOLUTION: A sludge treatment system in an embodiment concentrates primary sludge and excess sludge generated during sewage treatment at a water treatment facility, mixes them to obtain concentrated sludge, feeds the concentrated sludge into a digestion tank for anaerobic digestion, and uses the resulting digestion gas as fuel to heat water in a water heating device to generate heated water. The digested sludge extracted from the digestion tank is treated with a coagulant to coagulate and dehydrate it, producing dehydrated sludge and dehydrated filtrate, which are discharged. The discharged dehydrated filtrate is returned to the water treatment facility. The sludge treatment system includes a first heating part that heats concentrated excess sludge obtained by concentrating excess sludge using the heated water, a second heating part that heats the digestion tank using the heated water, a third heating part that heats digested sludge using the heated water, and a control part that controls the first heating part, the second heating part, and the third heating part, respectively.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present invention relate to a sludge treatment system and a sludge treatment method.

Background Art

[0002] One means of recovering energy from sewage sludge is anaerobic digestion. Generally, sewage sludge contains about 80% organic matter, and anaerobic digestion produces digested gas containing about 60% methane. In a conventional sludge treatment system that performs anaerobic digestion, a part of the organic matter in the sludge is converted into digested gas by anaerobic digestion in a digester into which thickened sludge is injected. Then, for example, the digested gas is used as fuel to generate hot water by a hot water heater, and the hot water is used to heat the digested sludge that circulates to the digester through a heat exchanger, thereby heating the digester to a temperature suitable for anaerobic digestion.

[0003] Also, the amount of heat required to heat the digester is affected by and varies with the outside air temperature. That required amount of heat becomes smaller in summer when the air temperature is high, and conversely becomes larger in winter when the air temperature is low. For this reason, the consumption of digested gas also becomes smaller in summer. The amount of digested gas generated depends on the amount and organic matter concentration of the thickened sludge input into the digester. Specifically, it is proportional to the product of the amount of thickened sludge and the organic matter concentration. Since the amount and organic matter concentration of the thickened sludge are derived from the amount and organic matter concentration of the influent sewage to the water treatment facility, and the amount and organic matter concentration of the influent sewage vary (so-called seasonal variation), the amount and organic matter concentration of the thickened sludge also vary. Therefore, the amount of digested gas generated also varies. When digested gas is generated in excess of the amount of heat required for heating the digester, etc., the unconsumed digested gas is disposed of, for example, as surplus gas in a surplus gas combustion device.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the sludge treatment system of the above-mentioned conventional technology, there is a problem that the digested gas that has not been consumed is disposed of and not effectively utilized. Since digested gas is a carbon-neutral fuel not derived from fossil fuels, electricity and heat (hot water, steam) derived from digested gas are renewable energies and do not increase greenhouse gas emissions. By using renewable energy, the amount of energy derived from fossil fuels can be reduced, thereby contributing to the reduction of greenhouse gas emissions.

[0006] The present invention has been made in view of the above circumstances, and an object thereof is to provide a sludge treatment system and a sludge treatment method capable of more effectively utilizing digested gas than in the past.

Means for Solving the Problems

[0007] The sludge treatment system of the embodiment inputs concentrated sludge obtained by concentrating and mixing primary sedimentation sludge and excess sludge generated in sewage treatment in a water treatment facility into a digestion tank for anaerobic digestion, and uses the generated digested gas as fuel to heat water in a water heating device to generate heated water. A flocculant is added to the digested sludge drawn out from the digestion tank for flocculation and dehydration to discharge dehydrated sludge and dehydrated filtrate, and the discharged dehydrated filtrate is returned to the water treatment facility. The sludge treatment system includes a first heating unit that heats concentrated excess sludge obtained by concentrating the excess sludge using the heated water, a second heating unit that heats the digestion tank using the heated water, a third heating unit that heats the digested sludge using the heated water, and a control unit that controls the first heating unit, the second heating unit, and the third heating unit, respectively.

Brief Description of the Drawings

[0008]

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Figure 11

DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments (first to fifth embodiments) of the sludge treatment system and the sludge treatment method of the present invention will be described in detail with reference to the drawings. In the following embodiments from the second embodiment onwards, descriptions of matters already described in the previous embodiments will be omitted as appropriate.

[0010] (Prior Art) To facilitate understanding of the embodiments, the prior art will be described again. FIG. 11 is a schematic configuration block diagram of a prior art sludge treatment system. In the description of FIG. 11, for the sake of brevity, descriptions of a thermometer, a valve, a flow meter, a system controller, etc. will be omitted as appropriate.

[0011] The primary settled sludge drawn from the primary sedimentation tank 101 of the water treatment facility and the excess sludge drawn from the final sedimentation tank 103 connected to the reaction tank 102 are treated by the sludge treatment system 10. The primary settled sludge is gravity thickened in a gravity thickening facility 11 (thickening tank). The excess sludge is thickened in a mechanical thickening facility 12 (thickener).

[0012] The thickened primary settled sludge drawn from the thickening facility 11 and the thickened excess sludge discharged from the thickening facility 12 are sent to a thickened sludge tank 17 (thickened sludge storage tank) and mixed to become thickened sludge. The thickened sludge is injected into the digestion tank 20, and a part of the organic matter in the thickened sludge is converted into digestion gas by anaerobic digestion. The undigested residue is discharged from the digestion tank 20 as digested sludge. Note that a gas holder for storing the digestion gas discharged from the digestion tank 20 may be provided.

[0013] The digestion gas discharged from the digestion tank 20 is supplied to a hot water heater 51 and a gas generator 26. The hot water heater 51 generates hot water using the digestion gas as fuel. Note that instead of the hot water heater 51, a boiler that generates steam using the digestion gas as fuel may be used.

[0014] The hot water generated by the hot water heater 51 heats the digested sludge that returns (circulates) from the digestion tank 20 to the digestion tank 20 via the heat exchanger 22, thereby heating the digestion tank 20 to a temperature suitable for anaerobic digestion. Here, it is assumed that a gas generator 26 is installed in order to utilize the digestion gas. The gas generator 26 generates electric power by gas power generation using the digestion gas as fuel. The digestion gas not consumed by the hot water heater 51 and the gas generator 26 is disposed of as excess gas in an excess gas combustion device 52.

[0015] The digested sludge discharged from the digester 20 is stored in the digested sludge storage tank 91, and a flocculant (polymer flocculant) is injected in the sludge flocculation tank 36 for flocculation. The flocculated sludge discharged from the sludge flocculation tank 36 is dehydrated by the sludge dehydrator 37 to become dehydrated sludge. The dehydrated filtrate separately discharged from the sludge dehydrator 37 is returned to the water treatment facility.

[0016] In such a sludge treatment system 10, as described above, there is a problem that the undigested biogas is disposed of by the surplus gas combustion device 52 and not effectively utilized. Therefore, hereinafter, a sludge treatment system and a sludge treatment method capable of more effectively utilizing biogas than in the prior art will be described.

[0017] (First Embodiment) FIG. 1 is a schematic configuration block diagram of the sludge treatment system 10 according to the first embodiment. The sludge treatment system 10 inputs the thickened sludge obtained by thickening and mixing the primary sludge and surplus sludge generated in the sewage treatment in the water treatment facility into the digester 20 for anaerobic digestion, uses the generated biogas as fuel to heat water in the water heating device to generate heated water, adds a flocculant to the digested sludge drawn from the digester 20 for flocculation and dehydration to discharge dehydrated sludge and dehydrated filtrate, and returns the discharged dehydrated filtrate to the water treatment facility. The sludge treatment system 10 includes each configuration shown in the figure. Hereinafter, each configuration will be described.

[0018] The gravity thickening facility 11 performs gravity thickening on the primary sludge drawn from the primary sedimentation obtained in the primary sedimentation tank 101 that receives the sewage treated by the standard activated sludge method, and discharges the thickened primary sludge. The sewage sent from the primary sedimentation tank 101 is sent to the reaction tank 102, and after the reaction in the reaction tank 102, it is sent to the final sedimentation tank 103.

[0019] The mechanical thickening facility 12 performs mechanical thickening on the final sludge drawn from the final sedimentation obtained in the final sedimentation tank 103, and discharges the thickened surplus sludge.

[0020] The hot water heater 53 (water heating device) heats water using digester gas as fuel to generate hot water. Note that instead of the hot water heater 53, a boiler (water heating device) that heats water using digester gas as fuel to generate steam may be used.

[0021] The heat exchanger 13 (first heating unit) performs heat exchange for heating the concentrated excess sludge using the hot water (heated water) from the hot water heater 53. The flow meter 14 detects the flow rate of the hot water supplied from the hot water heater 53 to the heat exchanger 13 and outputs a flow rate detection signal F1 to the system controller 38.

[0022] The valve 15 adjusts the flow rate of the hot water supplied from the hot water heater 53 to the heat exchanger 13 based on a valve control signal VC1 under the control of the system controller 38. The concentrated excess sludge thermometer 16 measures the temperature of the concentrated excess sludge supplied from the concentration facility 12 and outputs a concentrated excess sludge temperature signal T1 to the system controller 38.

[0023] The concentrated sludge tank 17 stores the concentrated primary sedimentation sludge supplied from the concentration facility 11 and the concentrated excess sludge supplied from the concentration facility 12. The concentrated excess sludge thermometer 18 measures the temperature of the concentrated excess sludge supplied from the concentration facility 12 and heated by the heat exchanger 13, and outputs a concentrated excess sludge temperature signal T2 to the system controller 38.

[0024] The concentrated sludge thermometer 19 measures the temperature of the concentrated sludge supplied from the concentrated sludge tank 17 to the digester 20, and outputs a concentrated sludge temperature signal T3 to the system controller 38. The digester 20 performs microbial treatment on the supplied concentrated sludge under anaerobic conditions with little oxygen, for example, digestion that decomposes it into digester gas containing methane gas, carbon dioxide, etc. by methane fermentation.

[0025] The digester thermometer 21 measures the temperature inside the digester 20 and outputs a digester temperature T4 to the system controller 38. The heat exchanger 22 (second heating unit) performs heat exchange for heating undigested thickened sludge in the digestion tank 20 using hot water or steam (heating water) from the waste heat boiler 28.

[0026] The flowmeter 23 detects the flow rate of the hot water supplied from the waste heat boiler 28 to the heat exchanger 22 and outputs a flow rate detection signal F2 to the system controller 38. The valve 24 adjusts the flow rate of the hot water supplied from the waste heat boiler 28 to the heat exchanger 22 based on the valve control signal VC2 under the control of the system controller 38.

[0027] The digested gas flowmeter 25 detects the flow rate of digested gas such as methane gas generated by digestion in the digestion tank 20 and outputs a flow rate detection signal F3 to the system controller 38. The gas generator 26 generates electric power by gas power generation using the supplied digested gas as fuel. The combustion exhaust gas thermometer 27 detects the temperature of the combustion exhaust gas of the gas generator 26 and outputs an exhaust gas temperature signal T5 to the system controller 38.

[0028] The waste heat boiler 28 is supplied with the combustion exhaust gas generated in the gas generator 26, and generates heating water (hot water, steam) by utilizing waste heat (performing heat recovery). Note that the combination of the gas generator 26 and the waste heat boiler 28 constitutes a water heating device. The pump 29 performs a pumping operation to supply the heating water generated by the waste heat boiler 28 to the heat exchanger 22.

[0029] The pump 54 performs a pumping operation to supply the heating water generated by the hot water heater 53 to the heat exchangers 13 and 32. The flowmeter 56 detects the flow rate of the hot water supplied from the hot water heater 53 to the heat exchangers 13 and 32 and outputs a flow rate detection signal F6 to the system controller 38. The valve 55 adjusts the flow rate of the hot water supplied from the hot water heater 53 to the heat exchangers 13 and 32 based on the valve control signal VC5 under the control of the system controller 38.

[0030] The heat exchanger 32 (the third heating unit) performs heat exchange for heating the digested sludge discharged from the digestion tank 20 using the hot water generated by the hot water heater 53. The flow meter 33 detects the flow rate of the hot water supplied from the hot water heater 53 to the heat exchanger 32 and outputs a flow rate detection signal F5 to the system controller 38. The valve 34 adjusts the flow rate of the hot water supplied from the hot water heater 53 to the heat exchanger 32 based on the valve control signal VC4 under the control of the system controller 38.

[0031] The digested sludge thermometer 35 detects the temperature of the digested sludge heated by the heat exchanger 32 and outputs a digested sludge temperature T6 to the system controller 38. The sludge coagulation tank 36 adds an appropriate amount of ferric polysulfate and a polymer coagulant to the supplied digested sludge to cause coagulation. The sludge dehydrator 37 dehydrates the sludge coagulated in the sludge coagulation tank 36 to obtain treated sludge (dehydrated sludge).

[0032] The system controller 38 (control unit) generates valve control signals and the like based on the various input signals, and controls the entire sludge treatment system 10. The system controller 38 controls the corresponding valves and the like for the heat exchanger 13, the heat exchanger 22, and the heat exchanger 32 respectively.

[0033] For example, the system controller 38 controls the supply amount of heating water (hot water, steam) to each of the heat exchanger 13, the heat exchanger 22, and the heat exchanger 32 according to the amount of digested gas discharged from the digestion tank 20.

[0034] Also, the system controller 38 controls the heat exchanger 13 to heat the concentrated surplus sludge at a temperature of 50°C or lower for 15 minutes (details will be described later).

[0035] Also, the system controller 38 controls the heat exchanger 32 to heat the digested sludge at a temperature lower than 70°C (details will be described later).

[0036] In addition, the system controller 38 may adjust the heating temperature of the digested sludge in the heat exchanger 32 based on the measured value of TOC (Total Organic Carbon) of EPS (Extracellular Polymertric Substance) extracted from the digested sludge heated in the heat exchanger 32.

[0037] In addition, when a flocculant is added to the digested sludge heated in the heat exchanger 32 and flocculated and dehydrated to discharge dewatered sludge and dewatered filtrate, the system controller 38 may adjust the heating temperature of the digested sludge in the heat exchanger 32 based on the measured value of TOC of the dewatered filtrate.

[0038] Next, the preliminary experiment will be described. As the preliminary experiment, experiments were conducted on the following three types of treatments (A) to (C). (A) Heat treatment of concentrated excess sludge (B) Heat treatment of the digester (C) Heat treatment of digested sludge (flocculation and dehydration treatment)

[0039] Hereinafter, the experiments of (A) and (C) will be described in detail. (A) Heat treatment experiment of concentrated excess sludge A digestion test of the heat-treated concentrated excess sludge was conducted, and the gas generation rate of the digested gas per amount of organic matter (VS amount) of the heat-treated concentrated excess sludge was determined. In addition, the increase amount of the gas generation rate with respect to the gas generation rate in the case without heat treatment was determined as the digested gas increase amount.

[0040] Figure 2 is an explanatory diagram of the experimental results of the heat treatment of concentrated excess sludge. As shown in Figure 2, the digested gas increase amount increased from the low temperature range to about 50°C. Also, in the high temperature range above about 50°C, although the digested gas increase amount decreased, it showed a higher gas generation rate than that without heating. And up to a maximum of 50°C, the digestibility of the excess sludge was improved by the heat treatment, and the gas generation rate was about 30 Nm 3It was suggested that the / t-VS increased. When this result was converted to concentrated sludge in which thickened excess sludge and thickened primary sedimentation sludge were mixed, the gas generation rate was 12 Nm 3 / t-VS corresponding to the increase.

[0041] Also, when the digestion rate was calculated from this gas generation rate, it was found that the digestion rate increased by 1.2 points when the excess sludge was heated to 50°C. It was also found that heating the thickened excess sludge at a temperature of 50°C or lower for 15 minutes was effective.

[0042] (C) Heat treatment experiment of digested sludge (coagulation dehydration experiment) When the treated sludge is heated in sludge dewatering treatment, the sludge viscosity decreases and the sedimentation property improves. As a result, it was predicted that when the treated sludge was heated, the moisture content of the dewatered sludge would decrease. Therefore, an aggregation dehydration experiment was carried out by heating the digested sludge drawn from the digester 20.

[0043] The aggregation dehydration was carried out by a two-liquid conditioning method in which ferric polysulfate and a polymer flocculant were added as flocculants for a simulation experiment. The aggregation dehydration experiment was carried out three times by changing the digested sludge and the heating temperature.

[0044] Figure 3 is an explanatory diagram of the results of the aggregation dehydration experiment of heating the digested sludge. As shown in Figure 3, although the moisture content of the dewatered sludge differed for each test because the properties of the digested sludge differed for each test, in the range from the low temperature range to about 70°C, it was found that in the same test, the moisture content of the dewatered sludge tended to decrease as the heating temperature increased. Also, heating was sufficient when the digested sludge reached a predetermined heating temperature, and a holding time was not necessary.

[0045] Thus, according to the first embodiment, it becomes possible to more effectively utilize the digestion gas than in the prior art. The details are as follows.

[0046] First, waste heat generated during power generation by the gas generator 26 is used as fuel to generate hot water and steam in the waste heat boiler 28, and the digested sludge circulating in the digester 20 is heated via the heat exchanger 22, thereby heating the digester 20 to an appropriate temperature. Also, a heat exchanger 13 is installed in the flow path of the concentrated excess sludge, and hot water (or steam generated by a boiler instead of the hot water heater 53) generated by the hot water heater 53 is circulated to heat the concentrated excess sludge to 50°C or lower (Figure 2). Among the primary sedimentation sludge and excess sludge generated in the sewage treatment, only the excess sludge with low decomposability in anaerobic digestion is heat-treated to enhance its digestibility.

[0047] Also, a heat exchanger 32 is installed in the flow path of the digested sludge, and hot water and steam generated by the waste heat boiler 28 are circulated to heat the digested sludge to a predetermined temperature. At this time, by heating the digested sludge at a temperature below 70°C, the moisture content of the dewatered sludge can be efficiently reduced (Figure 3).

[0048] In this way, the amount of digested gas can be increased and the volume of the dewatered sludge can be reduced.

[0049] (Second Embodiment) Next, the second embodiment will be described. Figure 4 is a schematic configuration block diagram of the sludge treatment system 10 of the second embodiment. In the first embodiment (Figure 1), hot water and steam generated by the waste heat boiler 28 are used to heat the digester 20 in the heat exchanger 22, and hot water generated by the hot water heater 53 is used to heat the concentrated excess sludge in the heat exchanger 13 and heat the digested sludge in the heat exchanger 32.

[0050] On the other hand, in the second embodiment (Figure 4), hot water and steam generated by the waste heat boiler 28 are used to heat the concentrated excess sludge in the heat exchanger 13 and heat the digested sludge in the heat exchanger 32, and hot water generated by the hot water heater 53 is used to heat the digester 20 in the heat exchanger 22.

[0051] In this way, the combination of the heat source and the heat exchanger can be changed.

[0052] (Third Embodiment) Next, the third embodiment will be described. FIG. 5 is a schematic configuration block diagram of the sludge treatment system 10 according to the third embodiment. A hot water heater 51 is installed instead of the gas generator 26 and the waste heat boiler 28 of the first embodiment (FIG. 1), and the digestion tank 20 is heated by the heat exchanger 22 using the hot water generated by the hot water heater 51. Alternatively, a boiler that generates steam may be installed instead of the hot water heater 51.

[0053] In this way, the type of heat source for supplying heat to the heat exchanger can be changed.

[0054] (Fourth Embodiment) Next, the fourth embodiment will be described. FIG. 6 is a schematic configuration block diagram of the sludge treatment system 10 according to the fourth embodiment. In the first embodiment, by heating the digested sludge in the range of less than 70°C, the water content of the dewatered sludge was reduced, and the amount of dewatered sludge discharged from the sludge treatment system 10 could be reduced. In the fourth embodiment (FIG. 6), the EPS extraction unit 61 extracts the EPS of the digested sludge after heating by the heat exchanger 32. The TOC measurement unit 62 measures the TOC of the EPS extracted by the EPS extraction unit 61. The system controller 38 adjusts the heating temperature of the digested sludge in the heat exchanger 32 based on the measurement value by the TOC measurement unit 62. This will be described in detail below.

[0055] The inventors have intensively studied the mechanism by which the water content of the dewatered sludge decreases due to the heating of the digested sludge and obtained the following findings. In the sludge of the sludge, there is an extracellular polymeric substance (EPS) composed of proteins, polysaccharides, humic substances, etc., and water is retained by the EPS. The types of water contained in the sludge are classified into three types: free water, interstitial water, and bound water. In addition, EPS is divided into three types: soluble EPS (S(Soluble)-EPS), loosely bound EPS (LB(Low Bound)-EPS), and tightly bound EPS (TB(Tightly Bound)-EPS).

[0056] Free water is water that is not bound to sludge. Interstitial water is water bound to sludge by surface tension and is released when the floc structure of the sludge is destroyed. Bound water is water scientifically bound to sludge and is intracellular water that exists only in living organisms, and is retained in S-EPS, LB-EPS, and TB-EPS, respectively.

[0057] The extraction of three fractions of EPS (S-EPS, LB-EPS, TB-EPS) from digested sludge samples with different heating temperatures was carried out as follows. The digested sludge sample was separated into a sediment and a supernatant by centrifugation. This supernatant was used as the S-EPS extract. To the remaining sediment, a 0.05% NaCl solution at 70 °C was added, stirred, and then separated into a sediment and a supernatant by centrifugation. This supernatant was used as the LB-EPS extract. To the remaining sediment, a 0.05% NaCl solution at 70 °C was added, heated at 60 °C for 30 min, and then separated into a sediment and a supernatant by centrifugation. This supernatant was used as the TB-EPS extract. The TOC of each extracted EPS extract was measured. The TOC was measured using an apparatus TOC-L (manufactured by Shimadzu Corporation).

[0058] Figure 7 is a table showing the results of TOC measurement of EPS extracted from digested sludge after heating. As can be seen from Figure 7, the higher the temperature of the digested sludge after heating compared to the temperature of the digested sludge before heating, the higher the TOC of each EPS tended to be. Also, in the comparison of each EPS, the TOC of S-EPS tended to be higher than that of LB-EPS and TB-EPS. Since each EPS showed a similar tendency with respect to the temperature after heating except for a part, the total of S-EPS, LB-EPS, and TB-EPS was evaluated as EPS.

[0059] Figure 8 is a graph showing the relationship between the temperature after heating and the TOC of the EPS extract. For the EPS in Tests 1 to 3, the TOC of the EPS increased as the temperature after heating increased. Therefore, it was suggested that the release of EPS was promoted as the heating temperature increased. Also, since EPS is assumed to have a high water retention capacity, it was considered that the release of EPS from the sludge improved the dewaterability of the sludge and led to a reduction in the water content of the dewatered sludge.

[0060] Therefore, it is considered that by extracting EPS from the digested sludge after heating, measuring the TOC, and adjusting the heating temperature based on the measured value, the high dewaterability of the digested sludge can be maintained more stably. The target temperature can be determined, for example, based on these experimental data and the like.

[0061] By adjusting the heating temperature in this way, the degree of EPS release from the digested sludge can be controlled, and the dewaterability of the digested sludge after heating can be stabilized. Here, Fig. 9 is a graph showing the relationship between the temperature after heating and the TOC of the S-EPS extract. From the comparison between Fig. 8 and Fig. 9, it was suggested that S-EPS and EPS show the same tendency. Also, since S-EPS has the highest concentration among each EPS (Fig. 7), in the EPS extraction in the EPS extraction section 61 of Fig. 6, the extraction may be limited to S-EPS, and EPS may be substituted with S-EPS.

[0062] (Fifth Embodiment) Next, the fifth embodiment will be described. Fig. 10 is a schematic configuration block diagram of the sludge treatment system 10 of the fifth embodiment. In the fourth embodiment (Fig. 6), EPS was extracted from the digested sludge after heating in the EPS extraction section 61, and the TOC was measured in the TOC measurement section 62. When EPS is S-EPS, EPS corresponds to the supernatant after centrifugation. Therefore, in the fifth embodiment (Fig. 10), more simply, the TOC of the dewatering filtrate discharged from the sludge dehydrator 37 is measured. The dewatering treatment of the sludge dehydrator 37 corresponds to the centrifugation treatment in the EPS extraction section 61.

[0063] At this time, the system controller 38 adjusts the heating temperature of the digested sludge in the heat exchanger 32 based on the measured value of the TOC by the TOC measurement section 62. In this way, a simpler system can be obtained.

[0064] The system controller 38 of the sludge treatment system 10 of the present embodiment includes a control device such as a CPU (Central Processing Unit), a storage device such as a ROM (Read Only Memory) and a RAM (Random Access Memory), an external storage device such as a semiconductor memory device exemplified by an HDD (Hard Disk Drive), a USB (Universal Serial Bus) memory, and an SSD (Solid State Drive), a display device such as a display device for displaying various information, and an input device such as a keyboard and a mouse, and has a hardware configuration using a normal computer.

[0065] The program executed by the system controller 38 of the present embodiment is provided by being recorded on a computer-readable recording medium such as a semiconductor memory device exemplified by a USB memory and an SSD, or a DVD (Digital Versatile Disk) in an installable format or an executable format file.

[0066] Alternatively, the program may be configured to be stored on a computer connected to a network such as the Internet and downloaded via the network. Further, the program may be configured to be provided or distributed via a network such as the Internet. Further, the program may be configured to be provided by being pre-installed in a ROM or the like.

[0067] The program has a module configuration including each functional configuration. As actual hardware, the CPU reads the program from the above storage medium and executes it, so that each functional configuration is loaded and generated on the main storage device.

[0068] Although some embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalent scope thereof.

Description of Reference Numerals

[0069] 10... Sludge treatment system, 11... Thickening equipment, 12... Thickening equipment, 13... Heat exchanger, 14... Flowmeter, 15... Valve, 16... Concentrated surplus sludge thermometer, 17... Concentrated sludge tank, 18... Concentrated surplus sludge thermometer, 19... Concentrated sludge thermometer, 20... Digester, 21... Digester thermometer, 22... Heat exchanger, 23... Flowmeter, 24... Valve, 25... Digester gas flowmeter, 26... Gas generator, 27... Combustion exhaust gas thermometer, 28... Waste heat boiler, 29... Pump, 30... Valve, 31... Flowmeter, 32... Heat exchanger, 33... Flowmeter, 34... Valve, 35... Digested sludge thermometer, 36... Sludge flocculation tank, 37... Sludge dewatering machine, 38... System controller, 51... Water heater, 52... Surplus gas combustion device, 53... Water heater, 54... Pump, 55... Valve, 56... Flowmeter, 61... EPS extraction unit, 62... TOC measurement unit, 91... Digested sludge storage tank

Claims

1. In a sewage treatment system in a water treatment facility, concentrated sludge obtained by concentrating and mixing primary sedimentation sludge and excess sludge generated in sewage treatment is fed into a digestion tank for anaerobic digestion, and the generated digestion gas is used as fuel to heat water in a water heating device to generate heated water. A flocculant is added to the digested sludge withdrawn from the digestion tank for flocculation and dehydration to discharge dehydrated sludge and dehydrated filtrate, and the discharged dehydrated filtrate is returned to the water treatment facility. The system is characterized by: A first heating unit that heats the concentrated excess sludge obtained by concentrating the excess sludge using the heated water; A second heating unit that heats the digestion tank using the heated water; A third heating unit that heats the digested sludge using the heated water; A control unit that controls the first heating unit, the second heating unit, and the third heating unit respectively; A sludge treatment system comprising the above components.

2. The sludge treatment system according to claim 1, wherein the water heating device includes at least one of a water heater that heats water using the digestion gas as fuel to generate warm water, and a boiler that heats water using the digestion gas as fuel to generate steam.

3. The sludge treatment system according to claim 2, wherein the water heating device further includes a gas generator that generates power by gas power generation using the digestion gas as fuel, and a waste heat boiler that uses the waste heat from the gas generator to heat water to generate warm water or steam.

4. The sludge treatment system according to claim 1, wherein the control unit controls the supply amount of the heated water to each of the first heating unit and the third heating unit according to the amount of the digestion gas.

5. The sludge treatment system according to claim 1, wherein the control unit controls the first heating unit to heat the concentrated excess sludge at a temperature of 50°C or lower for 15 minutes.

6. The sludge treatment system according to claim 1, wherein the control unit controls the third heating unit to heat the digested sludge at a temperature lower than 70°C.

7. The sludge treatment system according to claim 1, wherein the control unit adjusts the heating temperature of the digested sludge in the third heating unit based on the measured value of TOC (Total Organic Carbon) of EPS (Extracellular Polymertric Substance) extracted from the digested sludge after heating in the third heating unit.

8. The sludge treatment system of claim 1, wherein the control unit adjusts the heating temperature of the digested sludge in the third heating unit based on the measured TOC value of the discharged dehydrated filtrate when a coagulant is added to the digested sludge after heating in the third heating unit to coagulate and dehydrate the dehydrated sludge and the dehydrated filtrate are discharged.

9. A sludge treatment method using a sludge treatment system, comprising: concentrating and mixing primary sludge and excess sludge generated in sewage treatment at a water treatment facility, and then feeding the resulting concentrated sludge into a digestion tank for anaerobic digestion; heating water in a water heating device using the generated digestion gas as fuel to produce heated water; adding a flocculant to the digested sludge extracted from the digestion tank to perform flocculation and dehydration; discharging dehydrated sludge and dehydrated filtrate; and returning the discharged dehydrated filtrate to the water treatment facility, a step in which a control unit controls a first heating unit that heats concentrated excess sludge obtained by concentrating the excess sludge using the heated water; a step in which the control unit controls a second heating unit that heats the digestion tank using the heated water; a step in which the control unit controls a third heating unit that heats the digested sludge using the heated water; A sludge treatment method comprising:

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