JP6468958B2 - Sludge dewatering method and sludge dewatering system - Google Patents

Description

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

  The septic tank sludge produced in the septic tank that treats human waste and sewage and domestic wastewater, etc., collected in the toilet of the draw-up toilet, has a higher concentration of ammoniacal nitrogen than sewage treated at the sewage treatment plant. Are separately collected and then transported to a human waste treatment plant for processing.

  For example, in a human waste treatment plant, human waste and septic tank sludge are nitrified and denitrified by a biological denitrification method, and then treated by adding a flocculant.

  In such a human waste treatment plant, in order to maintain a constant sludge concentration (MLSS concentration) used in the biological denitrification method, a part of the growing sludge is removed from the human waste treatment as surplus sludge, In addition, agglomerated sediment sludge (hereinafter referred to as agglomerated sludge) that is precipitated and separated by the addition of a flocculant is removed from the human waste treatment. Therefore, surplus sludge and coagulated sludge are generated as human waste sludge in the human waste treatment plant.

  For example, human waste sludge is dehydrated by various dehydrators to prepare a dehydrated cake (sludge cake), and then incinerated.

  However, in recent years, a reduction in the moisture content of the dehydrated cake has been desired in order to reduce the running cost required for the incineration process.

  Thus, for example, a method of operating an electroosmotic dehydrator has been proposed in which sludge such as human waste sludge is dehydrated with an electroosmotic dehydrator to a moisture content of 70% or less (see, for example, Patent Document 1).

  In the operation method of such an electroosmotic dehydrator, sludge such as human waste sludge is separated into a dehydrated cake (solid content) having a moisture content of 70% or less and a dehydrated filtrate (liquid content).

JP 2011-5413 A

  Conventionally, human waste sludge generated from human waste treatment plants and sewage sludge generated from sewage treatment plants are dehydrated in separate sludge treatment facilities. However, from the viewpoint of equipment cost and running cost, it is desired to mix human waste sludge and sewage sludge and dehydrate them in a single sludge treatment facility.

  Thus, even when the target sludge mixed with human waste sludge and sewage sludge is dehydrated, a reduction in the moisture content of the dewatered cake is desired, and the target sludge mixed with human waste sludge and sewage sludge is used. Dehydration is studied by the operation method of the electroosmotic dehydrator described in Patent Document 1.

  However, when such target sludge is dehydrated by the operation method of the electroosmotic dehydrator described in Patent Document 1, the moisture content of the dehydrated cake may not be sufficiently reduced.

  Furthermore, since the dehydrated filtrate separated by sludge dehydration is returned to the human waste treatment plant and sewage treatment plant, suspended solids (Suspended Solid, hereinafter abbreviated as SS) in the dehydrated filtrate are sufficiently obtained. Removal, that is, improvement of SS recovery rate is desired.

  Accordingly, an object of the present invention is to provide a sludge dewatering method and a sludge dewatering system capable of improving the SS recovery rate while reducing the moisture content of the dewatered cake.

  [1] The present invention is a sludge dewatering method in which target sludge including sewage sludge and human waste sludge is dehydrated by an electroosmotic dehydrator, wherein the content ratio of the sewage sludge to the target sludge is 20 volumes. The sludge dewatering method comprises adjusting the electric conductivity of the target sludge to 400 mS / m or more and 700 mS / m or less, and then dehydrating with the electroosmotic dehydrator.

  However, since the electrical conductivity of human waste sludge is relatively higher than that of sewage sludge, human waste sludge can be reliably dehydrated by an electroosmotic dehydrator, reducing the moisture content of the dehydrated cake and The SS recovery rate can be improved.

  On the other hand, the target sludge having a sewage sludge content ratio of 20% by volume or more and 60% by volume or less contains sewage sludge having a relatively low electrical conductivity, resulting in a decrease in electrical conductivity. If the target sludge is dehydrated with an electroosmotic dehydrator, the moisture content of the dehydrated cake cannot be sufficiently reduced.

  Therefore, it is considered to adjust the electrical conductivity of the target sludge. However, if the electrical conductivity of the target sludge is higher than a predetermined value, electricity flows excessively to the target sludge and the SS recovery rate is reduced. There is a bug.

  On the other hand, according to said method, even if the content rate of a sewage sludge with respect to object sludge is 20 volume% or more and 60 volume% or less, the electrical conductivity of object sludge is set to 400 mS / m or more and 700 mS / m or less. After the adjustment, dehydration is performed by the electroosmotic dehydrator, so that the SS recovery rate can be improved while the moisture content of the target sludge (dehydrated cake) after dehydration can be reduced.

  [2] In addition, the present invention includes the sludge dewatering method according to the above [1], wherein a content ratio of the sewage sludge to the target sludge is 30% by volume or more and 55% by volume or less.

  According to such a method, since the content rate of the sewage sludge with respect to the target sludge is 30% by volume or more and 55% by volume or less, the water content of the dewatered cake can be reliably reduced.

  [3] In addition, the present invention includes the sludge dewatering method according to the above [2], wherein the electric conductivity of the target sludge is adjusted to 600 mS / m or less.

  According to such a method, since the electrical conductivity of the target sludge is adjusted to 600 mS / m or less, it is possible to suppress the excessive flow of electricity to the target sludge, and to improve the SS recovery rate reliably. .

  [4] The present invention also includes the sludge dewatering method according to any one of [1] to [3], wherein the voltage application time by the electroosmotic dehydrator is 200 seconds or less. .

  According to such a method, since the voltage application time by the electroosmotic dehydrator is 200 seconds or less, it is possible to suppress the excessive flow of electricity to the target sludge, and to further improve the SS recovery rate. Can be planned.

  [5] The present invention is a sludge dewatering system for carrying out the sludge dewatering method according to any one of [1] to [4] above, wherein the electrical conductivity of the target sludge is adjusted. A sludge dewatering system comprising a unit and an electroosmotic dehydrator for dewatering the target sludge having an adjusted electric conductivity.

  According to such a configuration, since the adjustment unit for adjusting the electric conductivity of the target sludge is provided, the electric conductivity of the target sludge can be reliably adjusted to 400 mS / m or more and 700 mS / m or less. The target sludge can be dehydrated with an electroosmotic dehydrator.

  Therefore, it is possible to improve the SS recovery rate while reducing the moisture content of the dehydrated cake.

  In the sludge dewatering method and sludge dewatering system of the present invention, the SS recovery rate can be improved while the moisture content of the dewatered cake can be reduced.

FIG. 1 is a schematic configuration diagram of a dewatering treatment facility as an embodiment of the sludge dewatering system of the present invention. FIG. 2A is a schematic configuration diagram of a sewage treatment plant that produces sewage sludge according to the sludge dewatering method of the present invention. FIG. 2B is a schematic configuration diagram of a human waste treatment plant for producing human waste sludge according to the sludge dewatering method of the present invention.

  One embodiment of the sludge dewatering method of the present invention includes a step (adjustment step) of adjusting the electrical conductivity of the target sludge including sewage sludge and human waste sludge, and a step of dehydrating the target sludge having the adjusted electrical conductivity ( Dehydration step).

  In such a sludge dewatering method, first, a target sludge containing sewage sludge and human waste sludge is prepared.

  The sewage sludge is sludge generated by a known sewage treatment plant, and is generated by, for example, the sewage treatment plant 70 shown in FIG. 2A.

  As shown in FIG. 2A, for example, the sewage treatment plant 70 includes an initial sedimentation tank 75, a reaction tank 76, a final sedimentation tank 77, and a flocculant addition tank 78.

  In the sewage treatment plant 70, first, sewage from the sewage system flows into the first sedimentation basin 75, and the first sedimentation basin 75 gravity settles the SS component having a relatively large specific gravity. Precipitates (such as SS having a relatively high specific gravity) generated in the initial sedimentation basin 75 are removed from the initial sedimentation basin 75 as initial sedimentation basin sludge (hereinafter referred to as initial sedimentation sludge). The sewage from which the initial settling sludge has been removed is sent from the first settling basin 75 to the reaction tank 76.

  In the reaction tank 76, the sewage flowing out from the first settling basin 75 is treated by the activated sludge method. Specifically, in the reaction tank 76, oxygen is supplied (aerated), and activated sludge containing aerobic microorganisms decomposes organic matter in sewage. At this time, the activated sludge in the reaction tank 76 grows with the decomposition of the organic matter. The sewage treated with activated sludge is sent from the reaction tank 76 to the final sedimentation basin 77.

  In the final sedimentation basin 77, the activated sludge contained in the sewage sent from the reaction tank 76 is gravity settled. Then, the activated sludge settled in the final sedimentation basin 77 is partially removed from the final sedimentation basin 77 as surplus sludge in order to keep the activated sludge concentration (MLSS concentration) in the reaction tank 76 constant. Is returned to the reaction tank 76 as return sludge. The supernatant in the final sedimentation basin 77 is sent from the final sedimentation basin 77 to the flocculant addition tank 78.

  In the flocculant addition tank 78, a known flocculant (for example, lime, aluminum salt, iron salt, polymer flocculant, etc.) is added to the supernatant liquid sent from the final sedimentation basin 77, and contamination in the supernatant liquid. Aggregate and precipitate substances (remaining organic matter, phosphorus, etc.). Then, the precipitate that precipitates in the flocculant addition tank 78 is removed from the flocculant addition tank 78 as flocculent sludge. Moreover, the supernatant liquid from which the coagulated sludge has been removed is discharged into public water areas such as rivers.

  Although not shown in the figure, the sewage treatment plant 70 may include a sand sink upstream of the first sedimentation basin 75 and may include a disinfection facility downstream of the final sedimentation basin 77.

  Further, in the sewage treatment plant 70, although not shown, the primary sedimentation sludge, surplus sludge and coagulated sludge can be transported to the anaerobic digestion tank, and the organic matter in the sludge can be decomposed by microorganisms in the anaerobic digestion tank. . In this case, the primary sedimentation sludge, excess sludge and coagulated sludge become digested sludge.

  The sewage sludge is sludge generated from each step of sewage treatment in a sewage treatment plant (for example, sewage treatment plant 70), and examples thereof include primary sedimentation sludge, excess sludge, coagulated sludge, and digested sludge. Such sewage sludge can be used alone or in combination of two or more, but preferably two or more types of sludge are used in combination.

  The electrical conductivity of such sewage sludge is relatively low compared to the electrical conductivity of human waste sludge.

  The human waste sludge is sludge generated by a known human waste treatment plant, and is generated by the human waste treatment plant 71 shown in FIG. 2B, for example.

  For example, as shown in FIG. 2B, the human waste treatment plant 71 includes a nitrification tank 85, a denitrification tank 86, a precipitation tank 87, and a flocculant addition tank 88.

  In the human waste treatment plant 71, first, the collected human waste, septic tank sludge and the like (hereinafter referred to as human waste sewage) are treated in the nitrification tank 85 and the denitrification tank 86 by a biological denitrification method.

  Specifically, human waste sewage is supplied to the nitrification tank 85. In the nitrification tank 85, oxygen is supplied (aerated). Under aerobic conditions, activated sludge containing nitrifying bacteria decomposes organic matter in human waste sewage and ammonia nitrogen in human sewage sewage. Is oxidized to nitrous acid or nitrate nitrogen. That is, human waste sewage is nitrified in the nitrification tank 85. At this time, the activated sludge in the nitrification tank 85 grows with the decomposition of organic matter and the oxidation of ammoniacal nitrogen. The nitrated sewage sewage is sent from the nitrification tank 85 to the denitrification tank 86.

  In the denitrification tank 86, dissolved oxygen does not exist and is maintained in an oxygen-free state in which only oxygen in nitrous acid or nitrate ions is present, and activated sludge containing denitrifying bacteria removes organic matter and the like being treated. While decomposing, nitrite or nitrate nitrogen in human waste sewage is reduced to nitrogen. That is, human waste sewage is denitrified in the denitrification tank 86. At this time, the activated sludge in the denitrification tank 86 grows with the decomposition of organic matter and the reduction of nitrous acid or nitrate nitrogen. The denitrified human waste sewage is sent from the denitrification tank 86 to the precipitation tank 87.

  In the sedimentation tank 87, the activated sludge (nitrifying bacteria and denitrifying bacteria) contained in the urine sewage sent from the denitrification tank 86 is gravity settled. The activated sludge that settles in the sedimentation tank 87 is removed from the sedimentation tank 87 as a part of the excess sludge in order to keep the activated sludge concentration (MLSS concentration) in the nitrification tank 85 and the denitrification tank 86 constant. The remaining portion is returned to the nitrification tank 85 as return sludge. The supernatant liquid in the precipitation tank 87 is sent from the precipitation tank 87 to the flocculant addition tank 88.

  In the flocculant addition tank 88, a known flocculant (for example, lime, aluminum salt, iron salt, polymer flocculant, etc.) is added to the supernatant liquid sent from the precipitation tank 87, and the pollutant in the supernatant liquid is added. Coagulate and precipitate (remaining organic matter, phosphorus, etc.). Then, the precipitate precipitated in the flocculant addition tank 88 is removed from the precipitation tank 87 as agglomerated sludge. Moreover, the supernatant liquid from which the coagulated sludge has been removed is discharged into public water areas such as rivers.

  Although not shown, the human waste treatment plant 71 may include a membrane separation device having a separation membrane such as a microfiltration membrane downstream of the flocculant addition tank 88. Further, in the case where the human waste treatment plant 71 includes a membrane separation device (not shown), without removing sludge in each of the precipitation tank 87 and the flocculant addition tank 88, in the membrane separation device (not shown), Separated into sludge components including excess sludge and agglomerated sludge and liquid components that permeate the separation membrane, a part of the sludge components is removed from the human waste treatment plant 71 as surplus sludge, and the remaining portion is returned to the nitrification tank as return sludge It can also be returned to 85.

  The human waste sludge is sludge generated from each step of human waste processing in the human waste treatment plant (for example, human waste treatment plant 71), and examples thereof include excess sludge and coagulated sludge. Such human waste sludge can be used alone or in combination of two or more. Among such human waste sludges, the combined use of excess sludge and agglomerated sludge is preferable.

  When the human waste sludge is a combination of excess sludge and agglomerated sludge, the content ratio (mass%) of the excess sludge is, for example, 2 times or more, preferably 4 times or more with respect to the content ratio (mass%) of the agglomerated sludge. For example, it is 10 times or less, preferably 6 times or less.

  The electric conductivity of such human waste sludge is, for example, 200 mS / m or more, and preferably 300 mS / m or more. In addition, the electrical conductivity of sludge can be measured with a commercially available electrical conductivity meter (for example, EC METER CM-14P manufactured by Toa DKK Corporation).

  And target sludge is prepared by stirring and mixing sewage sludge and human waste sludge.

  The content of sewage sludge with respect to 100% by volume of the target sludge is 20% by volume or more, preferably 30% by volume or more, more preferably 40% by volume or more and 60% by volume or less, preferably 55% by volume or less. .

  If the sewage sludge content is above the above lower limit, sewage sludge and urine sludge can be efficiently dehydrated collectively, and if the sewage sludge content is less than the above upper limit, the water content of the dewatered cake can be reduced. The SS recovery rate can be reliably improved while being able to be ensured.

  The suspended matter concentration (SS concentration) of the target sludge is, for example, 2000 mg / L or more, preferably 4000 mg / L or more.

  Next, the electric conductivity of the target sludge is adjusted to 400 mS / m or more and 700 mS / m or less.

  The electrical conductivity of the target sludge before adjusting the electrical conductivity is, for example, 150 mS / m or more, preferably 180 mS / m or more, for example, less than 400 mS / m, preferably 300 mS / m or less, more preferably 220 mS / m or less.

  Therefore, in order to adjust the electric conductivity of the target sludge within a predetermined range, for example, a conductive activator is added to the target sludge and stirred.

  Examples of the conductive activator include salts, acids, bases and the like, and preferably salts. Examples of the salts include alkali metal salts (for example, sodium chloride, sodium sulfate, sodium carbonate, potassium chloride and the like), and preferably sodium chloride. Such conductive activators can be used alone or in combination of two or more.

  Thereby, the electric conductivity of the target sludge is adjusted to 400 mS / m or more, preferably 430 mS / m or more, 700 mS / m or less, preferably 600 mS / m or less.

  If the electrical conductivity of the target sludge is equal to or higher than the above lower limit, the moisture content of the dewatered cake can be reliably reduced, and if the electrical conductivity of the target sludge is equal to or lower than the upper limit, the SS recovery rate is improved. be able to. On the other hand, when the electrical conductivity of the target sludge is less than 400 mS / m, the moisture content of the dewatered cake is remarkably increased, and when the electrical conductivity of the target sludge exceeds 700 mS /, the SS recovery rate is significantly decreased.

  In the adjustment step, an inorganic flocculant, a pH adjuster, a polymer flocculant, and the like can be added to the target sludge as necessary.

  When added to the target sludge, the inorganic flocculant electrically neutralizes the negative charges of the colloidal particles (for example, SS) in the sludge, and forms a floc in which the plurality of colloidal particles aggregate together.

  Examples of inorganic flocculants include aluminum flocculants (eg, aluminum sulfate, polyaluminum chloride, aluminum chloride, etc.), iron flocculants (eg, ferric chloride, polyferric sulfate, etc.), and the like. . Among inorganic flocculants, aluminum flocculants are preferable, and aluminum sulfate is more preferable. Such inorganic flocculants can be used alone or in combination of two or more.

  The addition ratio of the inorganic flocculant is, for example, 0.1% by mass or more, preferably 1% by mass or more, for example, 10% by mass or less, preferably 5% by mass or less, with respect to SS in the target sludge. .

  When the addition ratio of the inorganic flocculant is equal to or higher than the above lower limit, the SS recovery rate can be reliably improved, and when the addition ratio of the inorganic flocculant is equal to or lower than the upper limit, the moisture content of the dehydrated cake is reliably reduced. Can be aimed at.

  The pH adjuster is added to the target sludge so that the pH of the target sludge is, for example, 4.5 or more, preferably 5 or more, for example, 8 or less, preferably 7 or less.

  Examples of the pH adjuster include an acid adjuster (for example, sulfuric acid, hydrochloric acid, phosphoric acid, etc.), a basic adjuster (for example, sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, sodium bicarbonate, carbonic acid). Potassium, aqueous ammonia, etc.). Such pH adjusters can be used alone or in combination of two or more.

  In addition, when an inorganic flocculant is added to the target sludge, it is acidic (low pH) when the inorganic flocculant is dissolved in water. Therefore, a basic adjuster is preferably added to the target sludge. Of the basic regulators, sodium hydroxide is preferable.

  By adding the polymer flocculant to the target sludge, SS and dissolved substances in the sludge are supplementally adsorbed to form a floc. Such a floc is larger than a floc formed by an inorganic flocculant.

  Examples of polymer flocculants include cationic polymer flocculants (eg, acrylate polymer flocculants, methacrylate polymer flocculants, polyvinylamidines), anionic polymer flocculants (eg, sodium polyacrylate) Sodium acrylate and acrylamide copolymer, poly sodium methacrylate, sodium methacrylate and acrylamide copolymer, etc.), nonionic polymer flocculants (eg polyacrylamide, polyethylene oxide, etc.), amphoteric polymer agglomeration Agents (for example, a quaternized product of dimethylaminomethyl acrylate and a copolymer of acrylamide and acrylic acid, a quaternized product of dimethylaminomethyl methacrylate, a copolymer of acrylamide and acrylic acid, etc.). Such polymer flocculants can be used alone or in combination of two or more.

  Among such polymer flocculants, a cationic polymer flocculant is preferable.

  The addition ratio of the polymer flocculant is, for example, 0.2% by mass or more, preferably 0.5% by mass or more, for example, 5.0% by mass or less, preferably 2% with respect to SS in the target sludge. 0.0 mass% or less.

  Such a polymer flocculant is preferably used in combination with an inorganic flocculant from the viewpoint of improving the SS recovery rate. When the polymer flocculant and the inorganic flocculant are used in combination, the polymer flocculant is added to the target sludge after the inorganic flocculant is added to the target sludge.

  As a result, relatively small flocs formed by the inorganic flocculant are captured and adsorbed by the polymer flocculant to form relatively large flocs.

  In addition, when an inorganic flocculant and a pH adjuster are used together, the addition order of the inorganic flocculant and the pH adjuster is not particularly limited. When a pH adjuster and a polymer flocculant are used in combination, the polymer flocculant is added to the target sludge after the pH adjuster is added to the target sludge.

  That is, when a conductive activator, an inorganic flocculant, a pH adjuster and a polymer flocculant are used in combination, first, the conductive activator, the inorganic flocculant and the pH adjuster are added to the target sludge, and then the polymer flocculant is added. The agent is added to the target sludge.

  Next, the target sludge whose electric conductivity is adjusted is dehydrated.

  In order to dehydrate the target sludge, it is dehydrated (primary dehydration) with a mechanical dehydrator if necessary, and then dehydrated (secondary dehydration) with an electroosmotic dehydrator.

  Examples of the mechanical dehydrator include known mechanical dehydrators such as a pressure dehydrator (for example, a belt press dehydrator, a filter press dehydrator, a screw press dehydrator, a multi-disc dehydrator, etc.), a centrifugal Examples include dehydrators. Among the mechanical dehydrators, a pressure type dehydrator is preferable, and a multiple disk dehydrator is more preferable.

  When the target sludge is primarily dehydrated by a mechanical dehydrator, the water content of the target sludge after the primary dehydration is, for example, 80% by mass or more and 90% by mass or less. In addition, a moisture content can be measured with a commercially available moisture meter (for example, FD-610 etc. by Kett Science Laboratory Co., Ltd.).

  Examples of the electroosmotic dehydrator include known electroosmotic dehydrators, such as the electroosmotic dehydrator described in JP-A-2009-45587.

  More specifically, as shown in FIG. 1, for example, the electroosmotic dehydrator 46 includes a casing 53, an anode drum 56, a first roller 59, a second roller 60, a cathode belt 57, And a filter cloth 58.

  When referring to directions in FIG. 1, for the sake of convenience, the left side of the page is the front side, the right side of the page is the rear side, the upper side of the page is the upper side, the lower side of the page is the lower side, the front side of the page is the right side, and the back side of the page is the left side.

  The housing 53 has a substantially box shape. Further, a filtrate discharge port 54 is provided on the bottom wall of the casing 53, and a dehydrated cake discharge port 55 is provided on the rear wall of the casing 53.

  The anode drum 56 is disposed in the housing 53. The anode drum 56 is made of metal and has a substantially cylindrical shape extending in the left-right direction. The anode drum 56 can rotate in the counterclockwise direction when viewed from the right side with the axis as the center of rotation.

  The first roller 59 has a substantially cylindrical shape extending in the left-right direction, and a plurality of (four) first rollers 59 are arranged around the lower portion of the anode drum 56 with a space therebetween. The four first rollers 59 are arranged at intervals in the circumferential direction of the anode drum 56.

  The second roller 60 has a substantially cylindrical shape extending in the left-right direction, and is disposed on the opposite side of the anode drum 56 with respect to each of the four first rollers 59. The second roller 60 can rotate in the clockwise direction when viewed from the right side.

  The cathode belt 57 is a caterpillar endless belt made of metal. The cathode belt 57 is stretched around the four first rollers 59 and faces the lower peripheral surface of the anode drum 56 with a slight gap.

  The filter cloth 58 is permeable to moisture and has an endless belt shape. The filter cloth 58 is stretched around the four second rollers 60, and the center part in the front-rear direction of the upper part of the filter cloth 58 is disposed along the upper surface of the cathode belt 57. It is located between the belt 57.

  In order to dehydrate the target sludge with such an electroosmotic dehydrator 46, for example, the target sludge is supplied onto the filter cloth 58 on the front side of the anode drum 56, and then the four second rollers 60 are driven to rotate. The filter cloth 58 is moved. Then, the target sludge is sandwiched between the anode drum 56 and the cathode belt 57 (specifically, between the anode drum 56 and the filter cloth 58).

  Next, a DC voltage is applied between the anode drum 56 and the cathode belt 57.

  Then, since the sludge particles in the target sludge have a negative charge, the sludge particles are attracted to the anode drum 56 side, while the water in the target sludge has a positive charge. It passes through 58 and moves to the cathode belt 57 side.

  At this time, the applied voltage is, for example, 1 V or more, preferably 50 V or more, for example, 100 V or less, preferably 80 V or less.

  If the applied voltage is equal to or higher than the lower limit, the moisture content of the dehydrated cake can be reliably reduced. If the applied voltage is equal to or lower than the upper limit, the target sludge is excessively charged and the temperature of the target sludge is excessive. It can suppress that it rises. If the temperature of the target sludge rises excessively, some of the sludge particles are dissolved in moisture, and the SS recovery rate may decrease.

  The application time is, for example, 20 seconds or more, preferably 100 seconds or more, for example, 300 seconds or less, preferably 250 seconds or less, and more preferably 200 seconds or less.

  If the application time is equal to or greater than the above lower limit, it is possible to reliably reduce the moisture content of the dehydrated cake, and if the application time is equal to or less than the upper limit, it is possible to suppress excessive flow of electricity to the target sludge, and SS recovery. The rate can be improved with certainty.

  Further, the temperature of the anode drum 56 at the time of applying the DC voltage is, for example, 10 ° C. or more, preferably 80 ° C. or more, for example, 150 ° C. or less, preferably 120 ° C. or less.

  As a result, the target sludge is dehydrated by an electroosmotic dehydrator and separated into a dehydrated cake formed from sludge particles and a dehydrated filtrate.

  The water content of the dehydrated cake is, for example, 50% by mass or more, preferably 65% by mass or more, for example, less than 80% by mass, preferably 75% by mass or less, and more preferably 70% by mass or less.

  If the moisture content of the dehydrated cake is not less than the above lower limit, the running cost required for the incineration treatment of the dehydrated cake can be reliably reduced. In particular, when the moisture content of the dehydrated cake is 70% by mass or less, the dehydrated cake can be effectively used as a combustion aid.

  In such a sludge dewatering method, the SS recovery rate is, for example, 94% by mass or more, preferably 95% by mass or more, more preferably 96% by mass or more, and particularly preferably 97% by mass or more. 99.7% by mass or less. In addition, SS recovery rate can be measured with the following measuring methods.

SS recovery rate measurement method:
A glass fiber filter with a pore size of 1 μm is filtered and washed with water, put into a dryer, dried at 105 to 110 ° C. for 2 hours, allowed to cool with a desiccator, and then weighed.

  Next, the above glass fiber filter paper is attached to a filter, and an appropriate amount of the target sludge passed through a 2 mm mesh sieve is poured and suction filtered.

  While continuing the suction, wash away the suspended matter adhering to the filter wall onto the filter paper with water, wash the suspended matter with water several times, and as much water as possible.

  Next, the filter paper is removed from the filter, transferred to a watch glass, put into the dryer together with the watch glass, dried by heating at 105 to 110 ° C. for 2 hours, allowed to cool in a desiccator, and then the mass of the filter paper is measured.

  Next, the difference in the mass of the filter paper before and after filtration is obtained, and the SS concentration of the target sludge is calculated.

  Further, instead of the target sludge, the SS concentration of the dehydrated filtrate is calculated in the same manner as described above.

  Then, from the SS concentration of the obtained target sludge and dehydrated filtrate, the SS recovery rate (= (SS concentration of the target sludge × target sludge treatment amount per unit time−SS concentration of the dehydrated filtrate × dehydrated filtrate per unit time) Amount) / (SS concentration of target sludge × target sludge treatment amount per unit time) × 100).

  Such a sludge dewatering method is implemented, for example, by a dewatering treatment facility 1 as an example of a sludge dewatering system, as shown in FIG.

  The dehydration treatment facility 1 includes a sludge mixing unit 2, a dehydration pretreatment unit 3, and a dehydration unit 4.

  The sludge mixing unit 2 is disposed in the front portion (most upstream side) in the dehydration treatment facility 1. The sludge mixing unit 2 includes a mixing tank 7, a sewage sludge supply line 8, an excess sludge supply line 9, an agglomerated sludge supply line 10, a target sludge transport line 11, and a pump 12.

  The mixing tank 7 is a mixing tank that prepares target sludge by mixing sewage sludge and urine sludge, and has a substantially box shape. Although not shown, the mixing tank 7 is provided with a stirring member.

  The sewage sludge supply line 8 is a pipe that supplies sewage sludge to the mixing tank 7, and the downstream end of the sewage sludge supply line 8 is connected to the upper wall of the mixing tank 7.

  The surplus sludge supply line 9 is a pipe for supplying surplus sludge of human waste sludge to the mixing tank 7, and the downstream end of the surplus sludge supply line 9 is connected to the upper wall of the mixing tank 7.

  The agglomerated sludge supply line 10 is a pipe that supplies surplus sludge of human waste sludge to the mixing tank 7, and the downstream end of the agglomerated sludge supply line 10 is connected to the upper wall of the mixing tank 7.

  The target sludge transport line 11 is a pipe that transports the target sludge prepared in the mixing tank 7 to the dehydration pretreatment unit 3, and the upstream end of the target sludge transport line 11 is the lower end of the rear wall of the mixing tank 7. Connected to the department.

  The pump 12 is interposed in the middle of the target sludge transport line 11. Examples of the pump 12 include known liquid feed pumps such as a rotary pump and a reciprocating pump.

  The dehydration pretreatment unit 3 is disposed on the rear side (downstream side) of the sludge mixing unit 2. The dehydration pretreatment unit 3 includes a treatment tank 14, a conductivity adjustment unit 15 as an example of an adjustment unit, an inorganic flocculant addition unit 16, a pH adjustment unit 17, a polymer addition unit 18, and a target sludge transport line. 41 and a pump 42 are provided.

  The treatment tank 14 is a mixing tank in which various additives (for example, a conductive activator, an inorganic flocculant, a pH adjuster, a polymer flocculant, etc.) are added to and mixed with the target sludge transported from the sludge mixing unit 2. is there.

  The processing tank 14 includes a tank body 14A and a partition wall 14B.

  The tank body 14A has a substantially box shape. The partition wall 14B is disposed in the tank main body 14A, and partitions the internal space of the tank main body 14A into a front primary processing chamber 14C and a rear secondary processing chamber 14D.

  The downstream end of the target sludge transport line 11 is connected to the front wall of the tank main body 14A so as to communicate with the primary processing chamber 14C. Although not shown, the tank main body 14A is provided with a stirring member in each of the primary processing chamber 14C and the secondary processing chamber 14D.

  The conductivity adjusting unit 15 includes a conductive activator tank 20, an electrical conductivity measuring device 21, an activator transport line 22, and a pump 23.

  The conductive activator tank 20 has a substantially box shape and stores the conductive activator.

  The electrical conductivity measuring device 21 is a known electrical conductivity measuring device and can measure the electrical conductivity of the target sludge stored in the primary processing chamber 14 </ b> C of the processing tank 14.

  The activator transport line 22 is a pipe for transporting the conductive activator in the conductive activator tank 20 to the primary processing chamber 14C of the processing tank 14, and the upstream end of the activator transport line 22 is connected to the conductive activator tank. The downstream end of the activator transport line 22 is connected to the front portion of the upper wall of the tank body 14A so as to communicate with the primary processing chamber 14C.

  The pump 23 is interposed in the middle of the activator transport line 22. Examples of the pump 23 include the liquid feeding pump described above.

  The inorganic flocculant addition unit 16 includes a flocculant tank 26, a flocculant transport line 27, and a pump 28.

  The flocculant tank 26 has a substantially box shape and stores the inorganic flocculant.

  The flocculant transport line 27 is a pipe that transports the inorganic flocculant in the flocculant tank 26 to the primary processing chamber 14 </ b> C of the processing tank 14, and the upstream end of the flocculant transport line 27 is connected to the flocculant tank 26. Connected to the bottom wall, the downstream end of the flocculant transport line 27 is connected to the front portion of the upper wall of the tank body 14A so as to communicate with the primary processing chamber 14C.

  The pump 28 is interposed in the middle of the flocculant transport line 27. Examples of the pump 28 include the liquid feeding pump described above.

  The pH adjusting unit 17 includes a pH adjusting agent tank 32, a pH measuring device 33, a pH adjusting agent transport line 34, and a pump 35.

  The pH adjusting agent tank 32 has a substantially box shape and stores the pH adjusting agent.

  The pH measuring device 33 is a known pH measuring device, and can measure the pH of the target sludge stored in the primary processing chamber 14 </ b> C of the processing tank 14.

  The pH adjusting agent transport line 34 is a pipe for transporting the pH adjusting agent in the pH adjusting agent tank 32 to the primary processing chamber 14C of the processing tank 14, and the upstream end of the pH adjusting agent transport line 34 is pH adjusted. Connected to the bottom wall of the agent tank 32, the downstream end of the pH adjusting agent transport line 34 is connected to the upper wall of the tank body 14A so as to communicate with the primary processing chamber 14C.

  The pump 35 is interposed in the middle of the pH adjuster transport line 34. Examples of the pump 35 include the liquid feeding pump described above.

  The polymer addition unit 18 includes a polymer tank 38, a polymer transport line 39, and a pump 40.

  The polymer tank 38 has a substantially box shape and stores the above-described polymer flocculant.

  The polymer transport line 39 is a pipe for transporting the polymer flocculant in the polymer tank 38 to the secondary processing chamber 14D of the processing tank 14, and the upstream end of the polymer transport line 39 is connected to the polymer tank. The bottom end of the polymer transport line 39 is connected to the rear portion of the upper wall of the tank body 14A so as to communicate with the secondary processing chamber 14D.

  The pump 40 is interposed in the middle of the polymer transport line 39. Examples of the pump 40 include the liquid feeding pump described above.

  The target sludge transport line 41 is a pipe that transports the target sludge in the treatment tank 14 to the dehydration unit 4, and the tank main body so that the upstream end of the target sludge transport line 41 communicates with the secondary treatment chamber 14 </ b> D. It is connected to the lower end of the rear wall of 14A.

  The pump 42 is interposed in the middle of the target sludge transport line 41. Examples of the pump 42 include the liquid feeding pump described above.

  The dehydration unit 4 is disposed on the rear side (downstream side) of the dehydration pretreatment unit 3. The dehydration unit 4 includes a mechanical dehydrator 44, a supply unit 45, and the electroosmotic dehydrator 46 described above.

  The mechanical dehydrator 44 is a multiple disk dehydrator, and includes a frame 49 and a plurality of filter bodies 50.

  The frame 49 has a substantially box shape. The downstream end of the target sludge transport line 41 is connected to the front wall of the frame 49. The plurality of filter bodies 50 are accommodated in the frame 49. Each filter body 50 includes a plurality of discs arranged at intervals in the left-right direction, and a rotation shaft that collectively supports the plurality of discs.

  The plurality of filter bodies 50 include an upper filter body row 50A and a lower filter body row 50B. The upper stage filter body row 50A is configured by arranging a plurality of filter bodies 50 in a direction connecting the front lower side and the rear upper side. Each filter body 50 in the upper filter body row 50A is rotatable counterclockwise when viewed from the right side.

  The lower-stage filter body row 50B is arranged with a space on the lower side with respect to the upper-stage filter body row 50A, and a plurality of filter bodies 50 are arranged in a direction connecting the front lower side and the rear upper side. Yes. The interval between the upper filter body row 50A and the lower filter body row 50B becomes smaller toward the rear side (downstream side). Each filter body 50 in the lower filter array 50B is rotatable in the clockwise direction when viewed from the right side.

  The supply unit 45 is disposed on the rear side (downstream side) of the mechanical dehydrator 44 and includes a hopper 51 and a pair of supply rollers 52.

  The hopper 51 has a funnel-shaped hollow shape. Further, the upper part of the hopper 51 and the frame of the mechanical dehydrator 44 communicate with each other via the input communication port 61, and the lower part of the hopper 51 and the casing 47 of the electroosmotic dehydrator 46 are provided. Are communicated via the supply communication port 62.

  The pair of supply rollers 52 is disposed at the lower end of the hopper 51. Each supply roller 52 has a substantially cylindrical shape extending in the left-right direction. The pair of supply rollers 52 are arranged at an interval in the front-rear direction.

  Such a dehydration unit 4 may be a commercially available product (for example, Super Flakes (trade name) manufactured by Ataca Daiki Co., Ltd.).

  Next, the dehydration operation of the target sludge in the dehydration treatment facility 1 will be described.

  In the dehydration treatment facility 1, first, sewage sludge is supplied into the mixing tank 7 via the sewage sludge supply line 8, and surplus sludge of human waste sludge is supplied to the mixing tank 7 via the excess sludge supply line 9. Then, the coagulated sludge of human waste sludge is supplied into the mixing tank 7 via the coagulated sludge supply line 10.

  The supplied sewage sludge and human waste sludge are stirred and mixed by a stirring member (not shown) of the mixing tank 7.

  Thereby, the target sludge whose sewage sludge becomes said content rate is prepared.

  Next, the target sludge is transported from the mixing tank 7 to the primary processing chamber 14 </ b> C of the processing tank 14 through the target sludge transport line 11 by driving the pump 12.

  The target sludge transported to the primary processing chamber 14 </ b> C of the processing tank 14 is added with the conductive activator from the conductive activator tank 20 by the drive of the pump 23 at the above addition ratio.

  As a result, the electrical conductivity of the target sludge stored in the primary treatment chamber 14C is adjusted to the predetermined value. The electric conductivity of the target sludge can be confirmed by the electric conductivity measuring device 21.

  In addition, the inorganic flocculant from the flocculant tank 26 is added to the target sludge stored in the primary treatment chamber 14 </ b> C by the drive of the pump 28, and the pH is adjusted by driving the pump 35. The pH adjusting agent from the agent tank 32 is added at the above-described addition ratio.

  Thereafter, the target sludge stored in the primary processing chamber 14C is transferred from the primary processing chamber 14C to the secondary processing chamber 14D due to, for example, overflow.

  Then, the polymer flocculant from the polymer tank 38 is added to the target sludge transferred to the secondary processing chamber 14 </ b> D by the drive of the pump 40 at the above addition ratio.

  Next, the target sludge is transported from the secondary processing chamber 14 </ b> D of the processing tank 14 to the mechanical dehydrator 44 through the target sludge transport line 41 by driving the pump 42.

  The target sludge transported to the mechanical dehydrator 44 is sandwiched between the upper filter body row 50A and the lower filter body row 50B by the rotation of the plurality of filter bodies 50, and is primarily dehydrated.

  Thereafter, the primary dewatered target sludge is introduced into the hopper 51 of the supply unit 45 from the mechanical dehydrator 44 through the introduction communication port 61.

  Next, the target sludge is formed in a sheet shape by a pair of supply rollers 52, and is supplied to the electroosmotic dehydrator 46 from the supply communication port 62. Then, the sheet-like target sludge is disposed on the filter cloth 58 on the front side of the anode drum 56 and then reaches between the anode drum 56 and the cathode belt 57 as the filter cloth 58 moves.

  The target sludge is separated into a dehydrated cake and a dehydrated filtrate by electroosmosis by applying a DC voltage between the anode drum 56 and the cathode belt 57.

  Thereafter, the dewatered cake is discharged out of the electroosmotic dehydrator 46 from the dewatered cake discharge port 55 as the filter cloth 58 moves, and the dehydrated filtrate is electroosmotic dehydrated from the filtrate discharge port 54. It is discharged out of the machine 46.

  As described above, the target sludge is dehydrated by the dehydration treatment facility 1 and separated into the dehydrated cake and the dehydrated filtrate.

  Such a dehydration treatment facility 1 includes a control unit, drives each pump (pump 12, pump 23, pump 28, pump 35, pump 40, and pump 42), electrical conductivity measuring instrument 21, and pH measuring instrument. The 33 measurements can also be controlled electrically.

  The dehydration pretreatment unit 3 includes an inorganic flocculant addition unit 16, a pH adjustment unit 17, and a polymer addition unit 18 in addition to the conductivity adjustment unit 15. The unit 16, the pH adjustment unit 17, and the polymer addition unit 18 may not be provided.

  The dehydration unit 4 includes a mechanical dehydrator 44 and a supply unit 45 in addition to the electroosmotic dehydrator 46, but is not limited thereto, and does not include the mechanical dehydrator 44 and the supply unit 45. Also good.

2. In the above embodiment, after adjusting the target sludge having a sewage sludge content ratio of 20% by volume or more and 60% by volume or less so that the electric conductivity is 400 mS / m or more and 700 mS / m or less, Dehydrate with an electroosmotic dehydrator.

  However, in order to sufficiently reduce the moisture content of the dewatered cake, it is necessary to increase the electrical conductivity of the target sludge as the concentration of sewage sludge in the target sludge increases. On the other hand, if the electrical conductivity of the target sludge is excessively increased, the SS recovery rate decreases as the electrical conductivity increases.

  In this regard, according to the above embodiment, the content of sewage sludge with respect to the target sludge is 20% by volume or more and 60% by volume or less, and the electrical conductivity of the target sludge is 400 mS / m or more and 700 mS / m or less. After the adjustment, dehydration is performed by an electroosmotic dehydrator, so that the SS recovery rate can be improved while the moisture content of the dehydrated cake can be reduced.

  In particular, when the content ratio of sewage sludge to the target sludge is 30% by volume or more and 55% by volume or less, and the electrical conductivity of the target sludge is adjusted to 430 mS / m or more and 600 mS / m or less, the moisture content of the dehydrated cake is reduced. While the reduction can be reliably achieved, the SS recovery rate can be reliably improved.

  Moreover, if the voltage application time by the electroosmotic dehydrator is 200 seconds or less, it is possible to suppress the excessive flow of electricity to the target sludge, and the SS recovery rate can be improved more reliably.

  Moreover, the dehydration treatment facility 1 includes a conductivity adjusting unit 15 that adjusts the electrical conductivity of the target sludge, as shown in FIG. Therefore, the electric conductivity of the target sludge can be reliably adjusted to 400 mS / m or more and 700 mS / m or less, and the target sludge whose electric conductivity has been adjusted can be dehydrated by the electroosmotic dehydrator 46. As a result, it is possible to improve the SS recovery rate while reducing the moisture content of the dehydrated cake.

  The present invention will be described more specifically with reference to the following examples, but the present invention is not limited to them. Specific numerical values such as blending ratio (content ratio), physical property values, and parameters used in the following description are described in the above-mentioned “Mode for Carrying Out the Invention”, and the corresponding blending ratio (content ratio) ), Physical property values, parameters, etc., can be substituted with the upper limit values (numerical values defined as “below” or “less than”) or lower limit values (numerical values defined as “greater than”).

Examples 1-9
In the formulation shown in Table 1, sewage sludge, surplus sludge of human waste sludge, and agglomerated sludge of human waste sludge were stirred and mixed to prepare the target sludge. In Table 1, the excess sludge of human waste sludge and the aggregated sludge of human waste sludge are simply described as excess sludge and aggregated sludge, respectively.

  Next, sodium chloride (salts, conductive activator), sodium hydroxide (pH adjuster), and aluminum sulfate (inorganic flocculant) were added to the target sludge and stirred (adjustment step).

  As a result, the electrical conductivity and pH of the target sludge were adjusted as shown in Table 1. Moreover, the addition ratio of aluminum sulfate (inorganic flocculant) was 3 mass% with respect to SS in object sludge. Thereafter, a cationic polymer flocculant was added to the target sludge and stirred.

  Next, the target sludge was primarily dehydrated by the mechanical dehydrator 44 and then dehydrated by the electroosmotic dehydrator 46 in the dehydration unit 4 shown in FIG. As a result, the target sludge was dehydrated and separated into a dehydrated cake and a dehydrated filtrate.

  Table 1 shows the applied voltage and application time, the moisture content of the dehydrated cake, and the SS recovery rate in the electroosmotic dehydrator.

  In Table 1, the moisture content and SS recovery rate of the dehydrated cake were evaluated according to the following criteria.

  A: SS recovery rate is 95% by mass or more and water content is less than 70% by mass.

  ○: SS recovery rate is 95% by mass or more and water content is 70% by mass to 75% by mass.

  X: SS recovery rate is less than 95% by mass.

Comparative Examples 1 and 2
In the formulation shown in Table 1, surplus sludge of human waste sludge and agglomerated sludge of human waste sludge were stirred and mixed to prepare the target sludge.

  Next, sodium chloride (salts, conductive activator), sodium hydroxide (pH adjuster), and aluminum sulfate (inorganic flocculant) were added to the target sludge and stirred (adjustment step).

  As a result, the electrical conductivity and pH of the target sludge were adjusted as shown in Table 1. Moreover, the addition ratio of aluminum sulfate (inorganic flocculant) was 3 mass% with respect to SS in object sludge. Thereafter, a cationic polymer flocculant was added to the target sludge and stirred.

  Next, the target sludge was primarily dehydrated by the mechanical dehydrator 44 and then dehydrated by the electroosmotic dehydrator 46 in the dehydration unit 4 shown in FIG. As a result, the target sludge was dehydrated and separated into a dehydrated cake and a dehydrated filtrate.

Comparative Example 3
Except for changing the electrical conductivity of the target sludge as shown in Table 1 and changing the pH of the target sludge as shown in Table 1, in the same manner as in Example 8, It dehydrated and separated into a dehydrated cake and a dehydrated filtrate.

1 Dehydration Treatment Facility 15 Conductivity Adjustment Unit 46 Electroosmotic Dehydrator

Claims (5)

A method for dewatering sludge, wherein the target sludge including sewage sludge and human waste sludge is dehydrated by an electroosmotic dehydrator,
The content ratio of the sewage sludge with respect to the target sludge is 20% by volume or more and 60% by volume or less,
The method for dewatering sludge, wherein the electric conductivity of the target sludge is adjusted to 400 mS / m or more and 700 mS / m or less and then dehydrated by the electroosmotic dehydrator.   The sludge dewatering method according to claim 1, wherein a content ratio of the sewage sludge to the target sludge is 30% by volume or more and 55% by volume or less. The sludge dewatering method according to claim 2, wherein the electric conductivity of the target sludge is adjusted to 400 mS / m or more and 600 mS / m or less.   The sludge dehydration method according to any one of claims 1 to 3, wherein a voltage application time by the electroosmotic dehydrator is 200 seconds or less. A sludge dewatering system , comprising sewage sludge and human waste sludge, wherein the target sludge having a sewage sludge content ratio of 20 vol% to 60 vol% is dehydrated by an electroosmotic dehydrator ,
A treatment tank for storing the target sludge;
An adjustment unit for adjusting the electric conductivity of the target sludge;
An electroosmotic dehydrator for dehydrating the target sludge having an adjusted electrical conductivity ;
A control unit ,
The adjustment unit is
An electrical conductivity measuring device capable of measuring the electrical conductivity of the target sludge stored in the treatment tank;
An activator transport line for transporting the conductive activator to the treatment tank;
A pump that is provided in the activator transport line and adds the conductive activator to the target sludge by driving;
The controller is
The electrical conductivity of the target sludge is confirmed by the electrical conductivity measuring device, and the pump is driven so that the electrical conductivity of the target sludge is 400 mS / m or more and 600 mS / m or less. Dehydration system.

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