JP2007275790A - Sludge dewatering apparatus and sludge dewatering method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sludge dewatering apparatus and a sludge dewatering method which can sufficiently reduce the exhaust amount of dewatered/separated liquid produced in dewatering treatment of sludge. <P>SOLUTION: The sludge dewatering apparatus 10 is provided with: a flocculant solution preparing tank 2 where a flocculant and water are mixed to prepare a flocculant aqueous solution; an admixing part 3 where the flocculant aqueous solution from the flocculant solution preparing tank 2 and the sludge to be subjected to dewatering treatment are admixed; a dewatering means 4 where the admixture from the admixing part 3 is subjected to dewatering treatment; and a returning means L11 for returning at least a part of the dewatered-separated liquid separated from the admixture by the dewatering treatment in the dewatering means 4 to the flocculant solution preparing tank 2. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a sludge dewatering device and a sludge dewatering method.

  Sludge is usually dehydrated by adding a dehydrating aid to the sludge. Examples of the dehydration aid include a polymer flocculant and an inorganic flocculant, and one or both of these are added to the sludge. For example, Patent Document 1 describes a method of dewatering sludge using a polymer flocculant.

The polymer flocculant used as the dehydrating aid is a powder or a dispersion type or emulsion type liquid having a mass concentration of about 150 to 400 g / l. In order to sufficiently disperse the polymer flocculant in the sludge, the polymer flocculant is added to the sludge as an aqueous solution having an appropriate concentration. The mass concentration of the aqueous solution of the polymer flocculant is generally 1 to 2 g / l for the anionic system and 2 to 3 g / l for the cationic system. In this way, an aqueous solution of the polymer flocculant is prepared by dissolving or diluting the polymer flocculant with water.
Japanese Patent Publication No. 7-51240

  By the way, conventionally, clean water such as clean water and well water has been used as water for preparing an aqueous solution of a polymer flocculant having a predetermined concentration. These clean water is introduced from outside the sludge dewatering process. It is what is done. In order to obtain the above-described mass concentration of the polymer flocculant aqueous solution, it is necessary to introduce a considerable amount of clean water from outside the system.

  Moreover, it is common that the addition amount of the polymer flocculent with respect to sludge shall be 1-2 mass% on the basis of the total mass of the solid substance of sludge. For this reason, for example, when dewatering sludge having a high solid content such as methane fermentation sludge, a predetermined amount of the polymer flocculant corresponding to the solid content is added in the form of an aqueous solution. Therefore, as the amount of the polymer flocculant aqueous solution used increases, the amount of clean water introduced from outside the system in order to prepare the aqueous solution increases.

For example, a polymer flocculant is added to 100 m ^{3 of} sludge having a solid matter mass concentration of 50 g / l so that the addition amount of the polymer flocculant is 2% by mass based on the mass of the solid matter. In this case, the amount of the polymer flocculant aqueous solution added to the sludge is examined. Assuming that the powdered polymer flocculant is dissolved in water to prepare a polymer flocculant aqueous solution having a mass concentration of 2 g / l, the amount of the polymer flocculant aqueous solution is
[100 (m ³ ) × 50 (g / l) × 2 (mass%)] / 2 (g / l) = 50 (m ³ )
Is calculated. Thus, it is necessary to add the polymeric flocculant solution 50 m ³ with respect to wastewater 100 m ^3. Therefore, the amount of sludge after the addition of the polymer flocculant is 1.5 times that before the addition.

  As described above, when the amount of clean water introduced from outside the system increases, not only the load on the sludge dewatering machine increases, but also the flow load of the wastewater treatment facility provided at the subsequent stage of the sludge dewatering machine increases. Arise.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a sludge dewatering apparatus and a sludge dewatering method that can sufficiently reduce the discharge amount of the dewatered separation liquid generated in the sludge dewatering process. And

  The sludge dewatering device of the present invention mixes a flocculant solution preparation tank for mixing a flocculant and water to prepare an aqueous flocculant solution, and the flocculant aqueous solution from the flocculant solution preparation tank and the sludge to be dehydrated. A mixing unit, a dehydrating unit for dehydrating the admixture from the mixing unit, and a returning unit for returning at least part of the dehydrated separation liquid separated from the admixture by the dehydrating process in the dehydrating unit to the flocculant solution preparation tank It is characterized by providing.

  According to the sludge dewatering apparatus of the present invention, at least a part of the dewatered separation liquid is returned to the flocculant solution preparation tank and used for the preparation of the flocculant aqueous solution. For this reason, the amount corresponding to the return amount of the dehydrated separation liquid can be reduced with respect to the amount of drainage generated in the sludge dewatering apparatus according to the present invention. Thereby, the flow load of the waste water treatment facility provided in the subsequent stage of the sludge dewatering device can be reduced.

  The sludge dewatering device of the present invention preferably further comprises a removing means for removing suspended solids contained in the dehydrated separation liquid. This is because the dehydrated separation liquid in which the concentration of suspended solids is sufficiently reduced is more suitable as water used for the preparation of the flocculant aqueous solution than the dehydrated separation liquid having a high concentration. Using an aqueous polymer flocculant solution prepared using a dehydrated separation liquid in which the concentration of suspended solids is sufficiently reduced, the water content of the dehydrated sludge can be sufficiently reduced and suspended solids (hereinafter “SS”). The recovery rate can be sufficiently increased.

  Further, the sludge dewatering apparatus of the present invention is for preparing a clean water supply means for supplying clean water having a suspended solid concentration lower than the dehydrated separation liquid returned by the return means to the coagulant solution preparation tank, and for preparing the coagulant aqueous solution. It is preferable to further include a mixing ratio variable means capable of changing the mixing ratio of the clean water from the clean water supply means to be used and the dehydrated separation liquid returned by the return means.

  According to the sludge dewatering device provided with such clean water supply means and mixing ratio variable means, the dehydrated separation liquid and clean water can be mixed according to the SS concentration of the dehydrated separation liquid to be returned. This makes it possible to change the mixing ratio so that the SS concentration of water used for the preparation of the flocculant aqueous solution is a predetermined value or less.

  In the present invention, it is preferable to further include a mixing ratio control means for controlling the mixing ratio variable means. Thereby, it becomes easy to control the SS concentration of water used for the preparation of the flocculant aqueous solution to a predetermined value or less. The water content of the dewatered sludge can be sufficiently reduced and the recovery rate of the SS substance can be sufficiently increased by using an aqueous flocculant solution prepared using water having an SS concentration of a predetermined value or less. .

  In this invention, it is preferable to provide the density | concentration measurement means which measures SS density | concentration of the spin-drying | dehydration separation liquid returned to a flocculant solution preparation tank. According to the sludge dewatering device provided with such a concentration measuring means, it is possible to measure the SS concentration of the dehydrated separation liquid to be returned. Based on this measurement result, it becomes easy to automatically control the mixing ratio of the dehydrated separation liquid and the clean water by linking the mixing ratio variable means and the mixing ratio control means.

  Further, the SS concentration of water used for the preparation of the aqueous flocculant solution in the flocculant solution preparation tank is preferably 3000 mg / l or less. By using an aqueous flocculant solution prepared using water having an SS concentration of 3000 mg / l or less, the moisture content of the dewatered sludge can be sufficiently lowered and the recovery rate of the SS substance can be sufficiently increased. it can.

  In the sludge dewatering method of the present invention, a flocculant and water are mixed to prepare a flocculant aqueous solution in a flocculant solution preparation tank, and the flocculant aqueous solution and the sludge to be dehydrated are mixed. A dehydrating process for dehydrating the admixture, and a returning process for returning at least a part of the dehydrated separation liquid separated by the dehydrating process to the flocculant solution preparation tank. And

  According to the sludge dewatering method of the present invention, at least a part of the dewatered separation liquid is returned to the flocculant solution preparation tank and used for the preparation of the flocculant aqueous solution. For this reason, it is possible to reduce the amount corresponding to the return amount of the dehydrated separation liquid with respect to the amount of drainage of the dehydrated separation liquid generated by the sludge dewatering method according to the present invention. Thereby, the flow load of the waste water treatment facility provided in the subsequent stage of the sludge dewatering device can be reduced.

  ADVANTAGE OF THE INVENTION According to this invention, the discharge | emission amount of the dehydration separation liquid produced by the dehydration process of sludge can fully be reduced. For this reason, it is possible to sufficiently reduce the water load of the wastewater treatment facility that purifies the wastewater generated by the sludge dewatering treatment.

  Embodiments of the present invention will be described below. In addition, the same code | symbol is used for the same element and the overlapping description is abbreviate | omitted.

<First Embodiment>
First, with reference to FIG. 1, 1st Embodiment of the sludge dehydration apparatus which concerns on this invention is described. A sludge dewatering device 10 shown in FIG. 1 is configured to measure a sludge storage tank 1, a flocculant solution preparation tank 2, a mixing tank (mixing section) 3, a dehydrator (dehydrating means) 4, a dehydrated separation liquid tank 5, a pump, a flow meter, and the like. And automatic control means 15 for automatically controlling the operating conditions.

  The sludge storage tank 1 is a tank for storing sludge to be dehydrated (hereinafter, sometimes referred to as “treated sludge”). The flocculant solution preparation tank 2 is a tank for preparing an aqueous polymer flocculant solution to be added to the treated sludge. The mixing tank 3 is a tank for mixing the treated sludge and the polymer flocculant aqueous solution. The dehydrator 4 is an apparatus for dehydrating the mixture obtained in the mixing tank 3 and separating it into a dehydrated separation liquid and dehydrated sludge. The dehydration / separation liquid tank 5 is a tank for storing the dehydration / separation liquid separated by the dehydrator 4.

  The sludge storage tank 1 includes a line L1 for supplying sludge to the sludge storage tank 1 and a line L2 for transferring stored sludge to the mixing tank 3. The line L2 includes a pump P1 that supplies the treated sludge to the mixing tank 3 and a flow meter F1 that measures the flow rate of the treated sludge that flows in the line L2. The sludge supply means includes a sludge storage tank 1, a line L2, and a pump P1 and a flow meter F1 provided in the line L2.

  The flocculant solution preparation tank 2 includes a stirrer and is configured to be able to mix and stir the polymer flocculant and water. The flocculant solution preparation tank 2 includes a line L3 and a line L4 for supplying the polymer flocculant and clean water to the sludge dewatering device 10, respectively, and a line L5 for supplying the prepared polymer flocculant aqueous solution to the mixing tank 3. And. Line L3 is a flocculant supplier W1 that supplies a predetermined amount of polymer flocculant to the flocculant solution preparation tank 2, line L4 is a flow meter F3 that measures the flow rate of the supplied clean water, and an automatic valve V2 that adjusts the flow rate. Line L5 includes a pump P4 for transferring the polymer flocculant aqueous solution to the mixing tank 3, and a flow meter F2 for measuring the flow rate of the aqueous solution flowing in the line L5. The clean water supply means is constituted by a line L4 and an automatic valve V2 and a flow meter F3 provided thereto.

  The flocculant supply device W1 may have a suitable configuration depending on whether the polymer flocculant supplied through the line L3 is powder or liquid. When the polymer flocculant is a powder, a quantitative feeder and a weight meter can be used. When the polymer flocculant is a liquid, a level meter, a weight meter, a flow meter, and the like can be used.

  The mixing tank 3 includes a stirrer and is configured to be able to mix and stir the sludge to be treated and the polymer flocculant aqueous solution. In addition, the mixing tank 3 includes a line L6 for supplying a mixture of the treated sludge and the polymer flocculant aqueous solution to the dehydrator 4. As long as the sludge to be treated and the polymer flocculant aqueous solution can be mixed, the mixing part is not limited to the tank, and for example, the polymer flocculant aqueous solution is added to the sludge to be treated transferred in the line L2. You may add directly in the line L2.

  The dehydrator 4 includes a line L7 for transferring the dehydrated separated liquid and the dehydrated sludge separated from the admixture to the dehydrated separated liquid tank 5 and a line L8 for transferring them to the sludge treatment facility, respectively. As the dehydrator 4, any dehydrator can be applied, and examples thereof include a screw press dehydrator, a centrifugal dehydrator, a multiple disk dehydrator, a belt press dehydrator, a filter press dehydrator, a rotary press dehydrator, and the like. It is done. These dehydrators may be used alone or in combination of two or more.

  The dehydration / separation liquid tank 5 includes a line L <b> 9 for transferring the stored dehydration / separation liquid and a circulation line L <b> 10 for returning the dehydration / separation liquid to the dehydration / separation liquid tank 5. A pump P2 and a pump P3 are provided in the line L9 and the circulation line L10, respectively.

  The circulation line L10 includes a concentration measuring device (concentration measuring means) X1 that measures the SS concentration of the dehydrated separation liquid. As the concentration measuring device X1, a concentration measuring device having a configuration in which one or two or more selected from ultrasonic waves, infrared rays, microwaves, and laser beams are used in combination can be employed. The installation position of the concentration measuring device X1 is not limited to the circulation line L10 as long as the SS concentration of the dehydrated separation liquid returned to the flocculant solution preparation tank 2 can be measured. For example, the concentration measuring device X1 may be installed directly in the dehydrated separation liquid tank 5 or may be installed in a return line L11 described later.

  The dehydrated separation liquid stored in the dehydrated separation liquid tank 5 is discharged by the pump P2. Part or all of the dehydrated separation liquid discharged from the pump P2 is transferred to the flocculant solution preparation tank 2, and the dehydration separation liquid that is not transferred to the flocculant solution preparation tank 2 is transferred to a wastewater treatment facility.

  The return line L11 is a line that returns at least a part of the dehydrated separation liquid discharged from the pump P2 to the flocculant solution preparation tank 2. In this embodiment, the return means is constituted by a return line L11 and a pump P2.

  One end of the return line L11 is connected to the discharge side of the pump P2 of the line L9, and the other end is connected to the flocculant solution preparation tank 2. The return line L11 includes a flow meter F4 for measuring the flow rate of the dehydrated separation liquid to be returned and an automatic valve V1 for adjusting the flow rate.

  The automatic control means (mixing ratio control means) 15 is for automatically adjusting the supply amount of clean water to the flocculant solution preparation tank 2 and the return amount of the dehydrated separation liquid. The SS concentration of water used for preparing the polymer flocculant aqueous solution in the flocculant solution preparation tank 2 is adjusted by the automatic control means 15 to be within a suitable range.

  The automatic control means 15 is based on the data receiving unit 16 that receives the measurement values measured by the flow meter F3, the flow meter F4, and the concentration measuring device X1, and based on each measurement value received by the data receiving unit 16, And an instruction output unit 17 that outputs instructions for adjusting the opening degrees of the valve V2 and the automatic valve V1, respectively. The automatic control means 15 is configured using, for example, microcomputer hardware and software such as an ECU (Electric Control Unit). The mixing ratio variable means includes an automatic valve V1 and an automatic valve V2.

  Hereinafter, although the method of the dehydration process performed with the sludge dewatering apparatus 10 is demonstrated, the sludge, polymer flocculant, and clean water supplied to the sludge dewatering apparatus 10 are demonstrated prior to the description.

  Examples of the sludge supplied to the sludge storage tank 1 through the line L1 include organic sludge and inorganic sludge. Examples of the organic sludge include human waste, sewage sludge, sludge discharged from food / chemical / paper pulp mills, and the like. It is done.

  As the sludge to be dehydrated by the sludge dewatering apparatus 10, a solid material having a mass concentration of 20 to 300 g / l (more preferably 50 to 100 g / l) is suitable.

  Examples of the type of polymer flocculant supplied to the flocculant solution preparation tank 2 through the line L3 include anionic and cationic systems. Examples of the anionic polymer flocculant include acrylamide and sodium acrylate copolymer. Examples of cationic polymer flocculants include polydicyandiamide-based, polydiallylamine-based, polyamine-based copolymers, and polycondensates of dicyandiamide and formaldehyde. These polymer flocculants may be either powder or liquid. Examples of the liquid polymer flocculant include a dispersion type or emulsion type having a mass concentration of about 150 to 400 g / l.

  The clean water supplied to the flocculant solution preparation tank 2 through the line L4 is used to dilute the dehydrated separation liquid and reduce the SS concentration to the extent that it can be used for the preparation of the polymer flocculant aqueous solution. Therefore, the SS concentration of clean water needs to be lower than that of the dehydrated separation liquid returned by the return line L11. Since it is used in the above-mentioned applications, it is preferable that clean water has a lower SS concentration and evaporation residue concentration (hereinafter referred to as “TS concentration”) and is kept constant. For example, clean water, well water, Industrial water is suitable.

  Next, the method of sludge dehydration will be described in detail.

  The sludge stored in the sludge storage tank 1 is transferred to the mixing tank 3 as a treated sludge through the line L2 by the pump P1. The discharge amount of the pump P1 is measured by the flow meter F1, and is controlled by the inverter of the pump P1 so as to become a set value.

  The polymer flocculant and clean water are supplied to the flocculant solution preparation tank 2 through the line L3 and the line L4, respectively. Further, the dehydrating / separating liquid is supplied from the dehydrating / separating liquid tank 5 through the return line L11 to the flocculant solution preparation tank 2. In the flocculant solution preparation tank 2, the polymer flocculant, clean water, and dehydrated separation liquid are mixed to prepare an aqueous polymer flocculant solution (flocculant solution preparation step).

  The mass concentration of the aqueous polymer flocculant solution is preferably adjusted to be 1 to 2 g / l for the anionic system and 2 to 3 g / l for the cationic system.

  The polymer flocculant aqueous solution adjusted in the flocculant solution preparation tank 2 is transferred to the mixing tank 3 through the line L5 by the pump P4. The discharge amount of the pump P4 is measured by the flow meter F2, and is controlled by the inverter of the pump P4 so as to become a set value. The discharge amount of the pump P4 is set so that the mass of the polymer flocculant (dried state) contained in the polymer flocculant aqueous solution is 1 to 2% by mass based on the mass of the solid matter to be treated. It is preferable to do. In the mixing tank 3, when the mass of the polymer flocculant with respect to the solid matter of the sludge to be treated is less than 1% by mass, it tends to be difficult to sufficiently reduce the water content of the dewatered sludge. On the other hand, the polymer flocculant can be added in excess of 2% by mass, but the upper limit is preferably 2% by mass from the viewpoint of economy.

  In the mixing tank 3, the treated sludge and the polymer flocculant aqueous solution are mixed (mixing step). In the mixing step, from the viewpoint of further reducing the water content of the dewatered sludge, an inorganic flocculant may be added to prepare a mixture. Examples of the inorganic flocculant include iron-based and aluminum-based ones. When adding an inorganic flocculant, it is preferable to adjust the pH of the mixture to a suitable value by further adding a pH adjusting agent such as sodium hydroxide.

  The addition of the inorganic flocculant is not limited to the case of being performed in the mixing step, and the inorganic flocculant may be added to the treated sludge before being mixed or the treated sludge after being mixed. In addition, as the dehydrator 4 when the inorganic flocculant is added to perform the dehydration treatment, for example, a filter press, a screw press, a belt press, or the like is preferable.

  The admixture obtained in the mixing step is transferred to the dehydrator 4 via the line L6. The admixture is separated into a dehydrated separation liquid and dehydrated sludge by a dehydration process by the dehydrator 4 (dehydration process). The dehydrated separation liquid separated by the dehydration treatment is transferred to the dehydrated separation liquid tank 5 via the line L7. On the other hand, the dewatered sludge separated from the admixture is transferred to the sludge treatment facility via the line L8. Processing such as composting, carbonization or incineration of dewatered sludge is performed in the sludge treatment facility.

  The dehydrated separation liquid stored in the dehydrated separation liquid tank 5 is returned to the flocculant solution preparation tank 2 via the return line L11 (returning step). The amount of the dehydrated separation liquid to be returned to the flocculant solution preparation tank 2 is measured by the flow meter F4 and adjusted to the amount set by the automatic valve V1.

  The ratio of the amount of dehydrated separation liquid and clean water introduced into the flocculant solution preparation tank 2 can be set based on the SS concentration of the dehydrated separation liquid. Specifically, when the SS concentration of the dehydrated separation liquid is equal to or lower than a predetermined value, it is possible to cover the entire amount of water necessary for preparing the polymer flocculant aqueous solution with the dehydrated separation liquid. On the other hand, when the SS concentration of the dehydrated separation liquid exceeds a predetermined value, the SS concentration of water used for preparing the polymer flocculant aqueous solution (hereinafter referred to as “polymer flocculant-dissolved water”) is less than the predetermined value. Then, clean water is supplied to the flocculant solution preparation tank 2 through the line L4. The amount of clean water supplied to the flocculant solution preparation tank 2 is measured by the flow meter F3 and adjusted to the amount set by the automatic valve V2.

The predetermined value of the SS concentration of the polymer flocculant-dissolved water is preferably determined according to the characteristics of the sludge to be dehydrated. For example, when the sludge is methane fermentation sludge, it is empirically set to 3000 mg / l. Can do. The polymer flocculant-dissolved water has a TS concentration of 9000 mg / l or less, a chlorine ion concentration of 10,000 mg / l or less, an ammonia ion concentration of 4000 mg / l or less, an iron ion concentration (total amount of Fe ²⁺ and Fe ³⁺ ) of 100 mg / l or less, The pH is preferably 6-8.

  The suspended solids contained in the polymer flocculant-dissolved water, the dissolved matter such as chlorine ions, ammonia ions and iron ions, and the pH of the polymer flocculant-dissolved water are the water content of the dewatered sludge and the SS recovery rate in the sludge dewatering treatment. It will affect. For this reason, when the polymer flocculant-dissolved water having each concentration or pH outside the above range is used, the dewaterability tends to deteriorate.

  When the sludge dewatering apparatus 10 starts the sludge dewatering process, it is preferable to perform a process of dewatering the sludge to be dehydrated in advance and measuring the characteristics of the dewatered separation liquid (dehydrated separation liquid measuring process). Based on this result, the predetermined value of the SS concentration of the polymer flocculant-dissolved water can be determined in accordance with the property of the sludge provided to the sludge dewatering device 10. The characteristics of the dehydrated separation liquid to be measured include SS concentration, TS concentration, chlorine ion concentration, ammonia ion concentration, iron ion concentration and pH. For example, in the dehydration separation liquid measurement process, the sludge generated from the methane fermentation tank under various operating conditions is dehydrated, and the relationship between the SS concentration and TS concentration of the dehydration separation liquid and the moisture content of the dewatered dewatered sludge are measured. To do. Based on this result, a predetermined value of the SS concentration may be determined.

  FIG. 2 illustrates the relationship between the SS concentration and the TS concentration of the dehydrated separation liquid obtained by dehydrating methane fermentation sludge. These values are in a substantially proportional relationship, and in the case of this methane fermentation sludge, it can be seen that a value obtained by adding 5000 to 6000 to the SS concentration value becomes the TS concentration value. In this way, the TS concentration can be estimated by monitoring the SS concentration with the concentration measuring device X1 by conducting the dehydration separation liquid measurement step and examining the relationship between the TS concentration and the SS concentration of the dehydration separation liquid in advance.

  The SS concentration and TS concentration both affect the dewaterability of sludge. The reason for estimating the TS concentration value from the SS concentration measurement result is that automatic and continuous measurement of the TS concentration is difficult. Because.

  Furthermore, when the property of the sludge provided to the sludge dewatering device 10 changes over time, for example, when only the TS concentration of the dewatered separation liquid rises, the concentration measuring device X1 that monitors the SS concentration shows the change over time. I can't catch it. As the TS concentration of the dewatered separation liquid increases, the TS concentration of the polymer flocculant-dissolved water also increases, so that the dewaterability of sludge decreases.

  In order to prevent the above situation, it is preferable to appropriately perform a step of measuring the TS concentration of the dehydrated separation liquid (TS concentration measuring step). By resetting a predetermined value of the SS concentration based on the TS concentration measured in the TS concentration measurement step and the SS concentration by the concentration measuring device X1, dehydration can be performed under suitable conditions.

  Although the sludge dewatering apparatus according to the first embodiment has been described above, the sludge dewatering apparatus 10 may have the following form. For example, for the automatic control means 15, in addition to the measured values from the flow meter F3, the flow meter F4 and the concentration measuring device X1, the measured values from the coagulant supply device W1, the flow meter F1 and the flow meter F2 are received by the data receiving unit 16. It is good also as a structure received. And based on each measured value received by the data receiving unit 16, the opening degree of the automatic valve V2 and the automatic valve V1 from the instruction output unit 17, the flocculant supply device W1, the pump P1, the pump P2, the pump P3, and the pump A configuration may be adopted in which a discharge amount of 4 is set.

  Moreover, although the said embodiment is a structure which controls automatically the mixing ratio variable means comprised by the automatic valves V1 and V2, it uses a manual valve instead of an automatic valve, and these are manually controlled, and it is clean with a dehydration separation liquid. It is good also as a structure which controls the mixing ratio with water.

Second Embodiment
With reference to FIG. 3, 2nd Embodiment of the sludge dehydration apparatus which concerns on this invention is described. The sludge dewatering device 20 shown in FIG. 3 includes a precipitation tank 7 as a removing means for removing floating substances contained in the dewatered separation liquid, and further includes a precipitation separation liquid tank 9 in the subsequent stage. It differs from the sludge dewatering apparatus 10 which concerns on this. The sludge dewatering device 20 has a configuration in which the sedimentation tank 7 and the sediment separation liquid tank 9 are installed after the pump P2 of the line L9 of the sludge dewatering apparatus 10. Along with the provision of the sedimentation tank 7 and the sediment separation liquid tank 9, the installation position of the pump and the line connecting the components are also different from the sludge dewatering device 10. Hereinafter, these differences and the operation of the present embodiment derived therefrom will be described.

  The settling tank 7 is provided in the subsequent stage of the dehydrated separation liquid tank 5. The dehydrated separation liquid discharged from the pump P2 is supplied to the precipitation tank 7 through the line L9a. The sedimentation tank 7 precipitates the sludge scraper 18 for scraping the sludge settled on the bottom, the line L12 for returning the scraped sludge to the sludge storage tank 1, and the dehydrated separation liquid treated in the sedimentation tank 7. And a line L9b to be transferred to the separation liquid tank 9. The suspended matter contained in the dehydrated separation liquid is settled and concentrated in the sedimentation tank 7, and this is drawn out by the pump P <b> 5 and returned to the sludge storage tank 1. In this way, the SS concentration of the dehydrated separation liquid can be reduced. The sludge returned to the sludge storage tank 1 is again subjected to dehydration.

  In addition, as long as it can isolate | separate the suspended | floating substance contained in a spin-drying | dehydration separation liquid, it will not specifically limit to a precipitation tank, You may use a pressurized floating tank, a rotary screen, etc.

  The precipitation separation liquid tank 9 is a tank for storing the dehydrated separation liquid from the precipitation tank 7, and is provided in the subsequent stage of the precipitation tank 7. The precipitation separation liquid tank 9 includes a line L9c for transferring the stored dehydrated separation liquid and a circulation line L13 for returning the dehydration separation liquid to the precipitation separation liquid tank 9. A pump P6 and a pump P7 are provided in the line L9c and the circulation line L13, respectively.

  The circulation line L13 includes a concentration measuring device X2 that measures the SS concentration of the dehydrated separation liquid. As the concentration measuring device X2, one having the same configuration as that of the concentration measuring device X1 can be used. Further, the position of the concentration measuring device X2 is not limited to the circulation line L13 as long as the SS concentration of the dehydrated separation liquid returned to the flocculant solution preparation tank 2 can be measured. For example, the concentration measuring device X2 may be installed directly in the precipitation separation liquid tank 9, or may be installed in the return line L11.

  The dehydrated separation liquid stored in the precipitation separation liquid tank 9 is discharged by the pump P6. Part or all of the dehydrated separation liquid discharged from the pump P6 is transferred to the flocculant solution preparation tank 2, and the dehydration separation liquid that is not transferred to the flocculant solution preparation tank 2 is transferred to a wastewater treatment facility.

  In the present embodiment, at least a part of the dehydrated separation liquid discharged from the pump P6 is returned to the flocculant solution preparation tank 2 through the return line L11. In this embodiment, the return means is constituted by a return line L11 and a pump P6. One end of the return line L11 is connected to the discharge side of the pump P6 of the line L9, and the other end is connected to the flocculant solution preparation tank 2.

  In the present embodiment, the data receiving unit 16 of the automatic control means 15 is configured to receive respective measurement values measured by the flow meter F3, the flow meter F4, and the concentration measuring device X2. And the instruction | indication output part 17 outputs the instruction | indication which each adjusts the opening degree of the automatic valve V2 and the automatic valve V1 based on each measured value received by the data receiving part 16. FIG.

  According to the sludge dewatering device 20 according to the present embodiment, suspended substances contained in the dewatered separation liquid are removed in the settling tank 7. For this reason, even when the SS concentration of the dehydrated separation liquid separated by the dehydrator 4 is relatively high, this can be sufficiently reduced. Since the SS concentration of the dehydrated separation liquid is sufficiently reduced, the amount of clean water for diluting it can be further reduced.

  EXAMPLES The present invention will be specifically described below based on examples, but the present invention is not limited to the following examples.

  Using a device having the same configuration as the sludge dewatering device shown in FIG. 1, a cationic polymer flocculant was added to the methane fermentation sludge to perform dewatering treatment. The mass concentration of the solid contained in the methane fermentation sludge subjected to the dehydration treatment was 30 g / l on average. The polymer flocculant was added so that it might become 1.5 mass% with respect to the total mass of the sludge solid substance.

  Moreover, the automatic control apparatus was set so that when the dehydrated separation liquid with an SS concentration exceeding 3000 mg / l was returned to the flocculant solution preparation tank, clean water was supplied to the flocculant solution preparation tank.

  FIG. 4 is a graph showing changes in various parameters during the dehydration process. As shown in FIG. 4, the SS concentration of the dehydrated separation liquid was maintained at 2000 mg / l or less over the entire period (100 days) during the dehydration treatment. I was able to cover it. During the dehydration period, the water content of the dehydrated sludge was 60 to 70% by mass (based on the total mass of the dehydrated sludge), and the TS concentration of the dehydrated separation liquid was 8000 mg / l or less, and stable operation was possible. Further, the chlorine ion concentration, ammonia ion concentration, and pH of the dehydrated separation liquid were 1700 mg / l or less, 1600 mg / l or less, and 7.9 to 8.6, respectively.

It is a figure which shows the structure of 1st Embodiment of the sludge dehydration apparatus which concerns on this invention. It is a graph which illustrates the relationship between SS density | concentration of digested sludge, and TS density | concentration. It is a figure which shows the structure of 2nd Embodiment of the sludge dehydration apparatus which concerns on this invention. It is a graph which shows the fluctuation | variation of the various parameters during a dehydration process period.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10,20 ... Sludge dehydration apparatus, 1 ... Sludge storage tank (sludge supply means), 2 ... Coagulant solution preparation tank, 3 ... Mixing tank (mixing part), 4 ... Dehydrator (dehydration means), 5 ... Dehydration separation liquid tank , 7 ... Precipitation tank (removing means), 9 ... Precipitation separation liquid tank, 15 ... Automatic control means (mixing ratio control means), L4 ... Line (clean water supply means), L11 ... Return line (return means), V1, V2 ... Automatic valve (mixing ratio variable means), X1, X2 ... Concentration measuring device (concentration measuring means)

Claims (7)

A flocculant solution preparation tank for preparing an aqueous flocculant solution by mixing flocculant and water;
A mixing section for mixing the flocculant aqueous solution from the flocculant solution preparation tank and the sludge to be dewatered,
Dehydrating means for dehydrating the admixture from the mixing section;
A returning means for returning at least a part of the dehydrated separation liquid separated from the admixture by the dehydrating treatment in the dehydrating means to the flocculant solution preparation tank;
A sludge dewatering device comprising:   The sludge dewatering apparatus according to claim 1, further comprising a removing unit that removes suspended substances contained in the dehydrated separation liquid.   Clean water supply means for supplying clean water having a concentration of suspended solids lower than the dehydrated separation liquid returned by the return means to the flocculant solution preparation tank, and the clean water supply means used for preparing the flocculant aqueous solution The sludge dewatering apparatus according to claim 1 or 2, further comprising a mixing ratio variable means capable of changing a mixing ratio of the clean water from the dewatering liquid and the dehydrated separation liquid returned by the returning means.   The sludge dewatering apparatus according to claim 3, further comprising a mixing ratio control means for controlling the mixing ratio variable means.   The sludge dewatering device according to any one of claims 1 to 4, further comprising concentration measuring means for measuring a suspended solid concentration of the dehydrated separation liquid returned to the flocculant solution preparation tank.   The sludge dewatering according to any one of claims 1 to 5, wherein the suspended solid concentration of water used for the preparation of the flocculant aqueous solution in the flocculant solution preparation tank is 3000 mg / l or less. apparatus. A flocculant solution preparation step of mixing the flocculant and water and preparing an aqueous flocculant solution in the flocculant solution preparation tank;
A mixing step of mixing the flocculant aqueous solution with sludge to be dehydrated to obtain a mixture;
A dehydration step of dehydrating the admixture;
A return step of returning at least a part of the dehydrated separation liquid separated by the dehydration step to the flocculant solution preparation tank;
A sludge dewatering method comprising:

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