JP2016112546A - Dehydration method for sludge and dehydration device for sludge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dehydration method for sludge further reducing the water content of a dehydration cake and having a higher hydration effect.SOLUTION: Provided is a dehydration method for sludge comprising: a step where a flocculant having electric charges is added to sludge included in waste water; and a step where a fiber having electric charges is added after the step of adding the flocculant having electric charges, and the fiber having electric charges is added so as to be 3 wt.% or more by a dry weight ratio to the sludge.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a sludge dewatering method and a sludge dewatering apparatus. Specifically, the present invention relates to a dewatering method and a dewatering apparatus that enhance the dewatering effect of sludge by adding a flocculant and fibers to sludge contained in wastewater at a specific ratio.

  A large amount of sludge generated in the sewage treatment process and the factory wastewater treatment process is disposed of after being reduced in volume or reused after volume reduction. Examples of methods for reducing the volume of sludge include mechanical dehydration, drying, and incineration. Among them, the mechanical dehydration method is an energy-saving and simple method, and thus is performed alone or in combination with other methods.

  The sludge after dehydration is called dehydrated cake, and it is desired that the water content of the dehydrated cake be as low as possible. By keeping the moisture content of the dehydrated cake low, the amount of sludge to be disposed can be reduced, and the transportation cost and storage cost can be reduced. Moreover, when drying or incinerating sludge after dehydration, auxiliary fuel such as heavy oil or coal powder may be used to evaporate water in the sludge. In such a case, the amount of auxiliary fuel used can be reduced by keeping the moisture content of the dehydrated cake low.

  In mechanical dewatering of sludge, it is generally performed to add flocculant to sludge to form flocs and then squeeze. Moreover, it is known that the water content of the dehydrated cake can be reduced by adding fibers as a dehydration aid. For example, Patent Documents 1 to 3 disclose a sludge dewatering method including a step of adding a flocculant and fibers to sludge. In Patent Document 1, fibers are added to sludge as a dehydrating aid, and the addition rate in this case is less than 3% by weight with respect to the solid content (dry weight) of the sludge. In patent document 2, 3-10 weight% of fibers are added with respect to the solid content (dry weight) of sludge. In Patent Document 3, a waste paper pulverized product is added to sludge as a dehydrating aid, and the addition rate of the waste paper pulverized product is 6.2 to 40% by weight based on the solid content (dry weight) of the sludge. In Patent Document 2, there is no particular limitation on the order of adding the flocculant and the waste paper pulverized product. Moreover, in the Example of patent document 3, after adding a waste paper ground material, the process of adding a flocculant is provided.

JP 2014-69145 A JP 2010-436 A Japanese Patent No. 3485138

  As described above, it has been studied to increase the dewatering effect of sludge by adding fibers so as to have a predetermined addition rate with respect to the solid content of the sludge. However, even in the conventional dehydration method, the dehydration effect is not sufficient, and further improvement has been demanded. In addition, when the conventional dehydration method is used, it is difficult to sufficiently reduce the amount of sludge after dehydration (the amount of dehydrated cake), and further improvement has been demanded in this regard.

  Therefore, in order to solve the problems of the prior art, the present inventors have further studied for the purpose of further reducing the moisture content of the dewatered cake and providing a sludge dewatering method with a higher dewatering effect. . Furthermore, the inventors of the present invention have also studied for the purpose of sufficiently reducing the amount of sludge after dehydration (the amount of dehydrated cake).

As a result of intensive studies to solve the above problems, the present inventors have added dehydration by adding a flocculant having a charge and a fiber having a charge to the sludge contained in the wastewater in a predetermined order. It has been found that the moisture content of the cake can be reduced and the amount of sludge after dehydration (the amount of dehydrated cake) can also be reduced.
Specifically, the present invention has the following configuration.

[1] A fiber having a charge, which includes a step of adding a flocculant having a charge to sludge contained in wastewater, and a step of adding a fiber having a charge after the step of adding a flocculant having a charge. The sludge dewatering method is characterized by being added to the sludge so that the dry weight ratio is 3% by weight or more.
[2] The sludge dewatering method according to [1], wherein the charged fibers are added to the sludge so that the dry weight ratio is 5 to 70% by weight.
[3] The sludge dewatering method according to [1] or [2], wherein the charged fibers are added to the sludge so that the dry weight ratio is more than 10% by weight and 70% by weight or less.
[4] The method according to any one of [1] to [3], further including a concentration treatment step after the step of adding an aggregating agent having a charge, and further including a step of adding a fiber having a charge after the concentration treatment step. Substrate sludge dewatering method.
[5] The sludge dewatering method according to any one of [1] to [4], wherein the charged fibers are wood-derived pulp.
[6] The sludge dewatering method according to any one of [1] to [5], wherein the charged fiber is a hardwood-derived pulp.
[7] The sludge dewatering method according to any one of [1] to [6], wherein the flocculant is at least one selected from a cationic flocculant and an anionic flocculant.
[8] A means for adding a flocculant having a charge to sludge contained in waste water and a means for adding a fiber having a charge to sludge containing the flocculant, wherein the means for adding a fiber having a charge is a charge A sludge dewatering apparatus, wherein the sludge dewatering device is a means for adding so that the ratio of the fibers having a dry weight ratio to the sludge is 3% by weight or more.
[9] The sludge according to [8], wherein the means for adding the charged fiber is a means for adding the charged fiber so that the ratio of the charged fiber is 5 to 70% by weight with respect to the sludge. Dehydration equipment.
[10] The sludge dewatering device according to [8] or [9], further comprising means for concentrating the sludge containing the flocculant.

  By using the dehydration method of the present invention, the moisture content of the dehydrated cake can be sufficiently reduced. Moreover, by using the dehydration method of the present invention, the amount of sludge after dehydration (the amount of dehydrated cake) can be sufficiently reduced.

FIG. 1 is a schematic diagram illustrating a sludge dewatering method and dewatering apparatus according to the present invention.

  Hereinafter, the present invention will be described in detail. The description of the constituent elements described below may be made based on representative embodiments and specific examples, but the present invention is not limited to such embodiments. In the present specification, a numerical range expressed using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

(Sludge dewatering method)
The present invention relates to a method for dewatering sludge comprising a step of adding a flocculant having a charge to sludge contained in wastewater, and a step of adding a fiber having a charge after the step of adding a flocculant having a charge. . Here, the charged fibers are added to the sludge so that the dry weight ratio is 3% by weight or more.

  In the present invention, as described above, a floc having a high density can be formed in an intermediate step by adding a flocculant having a charge and a fiber having a charge in a specific order. By forming such flocs, the moisture content of the dehydrated cake can be effectively reduced. Furthermore, by adding the fiber ratio within the above range, in addition to enhancing the dehydration effect, the amount of sludge after dehydration (dehydrated cake amount) can be sufficiently reduced. Usually, when the fiber addition rate is increased, a large amount of fiber is contained in the dehydrated cake, and there is concern about an increase in the amount of sludge. However, in the present invention, surprisingly, by adding the fibers so as to be 3% by weight or more, not only the dehydration effect is enhanced, but also the sludge amount (dehydrated cake amount) can be reduced.

  FIG. 1 is a schematic view illustrating the sludge dewatering method of the present invention. The sludge is first transferred to the agglomeration tank 10. The aggregating tank 10 is provided with a stirrer 12. Further, a flocculant storage tank 20 is connected to the aggregation tank 10. After the sludge has been transferred to the coagulation tank 10, the coagulant is fed from the coagulant storage tank 20 and charged into the coagulation tank 10. Thereafter, the sludge and the flocculant are uniformly mixed by being stirred by the stirrer 12. In addition, when two or more kinds of flocculants are added to the sludge, the flocculant tank 10 may include a plurality of flocculant storage tanks 20.

  Next, the sludge mixed with the flocculant in the coagulation tank 10 is transferred to the sludge volume reduction tank 15. The sludge volume reducing tank 15 is also equipped with a stirrer 17, and a fiber storage tank 30 is connected to the sludge volume reducing tank 15. After the sludge containing the flocculant is transferred to the sludge volume reducing tank 15, the charged fibers are fed from the fiber storage tank 30 to the sludge volume reducing tank 15. Then, the sludge, the flocculant, and the fiber are uniformly mixed by being stirred by the stirrer 17. Thus, in this invention, after a flocculant is mixed with sludge, a flocculant containing sludge is transferred to a sludge volume reduction tank, and is mixed with the fiber which has an electric charge there. By adopting such an addition order, sludge can be effectively dehydrated.

  In the coagulation tank 10, the total stirring time after the coagulant is mixed is preferably 30 minutes or more, and more preferably 10 minutes or more. When the total stirring time is, for example, 10 minutes, the fast stirring time is preferably 2 minutes, and the slow stirring time is preferably 8 minutes. In this case, the stirring property (mixing property) of the flocculant or fiber can be promoted by rapid stirring, and floc formation can be promoted by gentle stirring. Here, the gentle stirring is a condition for stirring at a speed of 20 to 50% of the stirring speed of fast stirring. Specifically, when the rapid stirring is 200 rpm, the slow stirring is 40 to 100 rpm. In addition, the stirring conditions with the fiber in the sludge volume reduction tank 15 are the same as the above.

  The flocculant storage tank 20 and the fiber storage tank 30 measure the weight of the sludge stored in the flocculant tank 10 and the sludge volume reduction tank 15, respectively, and calculate the amount of the flocculant and fibers to be input from the weights. It is preferable to have a system that does this.

  In the present invention, as described above, it is preferable to include the flocculation tank 10 and the sludge volume reducing tank 15, but only one of the tanks may be provided. For example, when only the coagulation tank 10 is provided, both the coagulant storage tank 20 and the fiber storage tank 30 are connected to the coagulation tank 10. And it is good also as adding a fiber, after first adding a flocculant to the sludge transferred to the coagulation tank 10, and performing stirring. Thus, you may adjust an addition order by shifting the addition time of a business agent and a fiber.

  The sludge mixed with the flocculant and the fibers is transferred to the dehydrator 40. In the dehydrator 40, moisture is removed from the sludge using a dehydration system such as a screw press, a filter press, a centrifugal dehydrator, a belt press, or an electroosmotic dehydrator. Among these, as the dehydrator 40, a screw press is preferably used. Dehydration may be performed by combining a plurality of dehydration systems. For example, centrifugal dehydration may be performed after a screw press. The water removed from the sludge is discharged as treated water. In addition, the dewatered sludge becomes a dehydrated cake and is reused as a fertilizer or discarded.

  In the sludge dewatering method of the present invention, it is preferable that the method further includes a concentration treatment step after the step of adding the charged flocculant, and the step of adding the charged fiber after the concentration treatment step. In the concentration treatment step, concentration is preferably performed by a coagulation sedimentation treatment, a pressure levitation treatment, a centrifugal separation treatment, or the like. After providing such a treatment step, sludge and fibers can be efficiently mixed by adding fibers having electric charges.

  The charged fibers may be added as a slurry. In the slurry, the charged fibers are uniformly dispersed. The slurry only needs to contain 0.1 to 15% by weight of fibers, and preferably contains 1 to 10% by weight. In addition, you may contain additives, such as a dispersing agent, as needed. By adding the fibers in a slurry state, the sludge and pulp can be mixed uniformly. Thereby, the moisture content of a dewatering cake can be reduced more effectively. Moreover, by making pulp into a slurry, the addition work can be facilitated, and the work efficiency of the dehydration treatment can be increased.

  The charged fibers may be added to the sludge so that the dry weight ratio is 3% by weight or more. Moreover, it is preferable that the addition rate of the fiber which has an electric charge is 5-70 weight%, It is more preferable that it is more than 10 weight% and 70 weight% or less, It is further more preferable that it is 15-70 weight%. By making the addition rate of the fiber having an electric charge within the above range, the moisture content of the dehydrated cake can be more effectively reduced, and the amount of sludge (dehydrated cake amount) can also be reduced.

When calculating the ratio of fiber to sludge, first, the dry weight of sludge is measured by the following method.
(1) Dewater sludge.
(2) The dehydrated sludge is sandwiched between filter papers and a 5 kg weight is placed on the filter for 10 minutes to absorb moisture.
(3) The sludge is dried for 24 hours in a dryer at 105 ° C.
(4) The sludge concentration is calculated from the amount of sludge before dehydration and the amount of dried sludge after drying.
Sludge concentration (%) = amount of sludge after drying (g) ÷ amount of sludge before dehydration (g) x 100
Next, when the fiber is added as a slurry, the fiber concentration is calculated by the same method as described above. In addition, when adding a fiber as a solid pulp, the weight of a solid pulp becomes dry fiber amount (g).
(1) The fiber slurry is dehydrated.
(2) The dehydrated fiber slurry is sandwiched between filter papers and a 5 kg weight is placed on it for 10 minutes to absorb moisture.
(3) The fiber slurry is dried in a dryer at 105 ° C. for 24 hours.
(4) The fiber slurry concentration is calculated from the fiber slurry amount before dehydration and the dry fiber slurry amount after drying.
Fiber slurry concentration (%) = fiber slurry amount after drying (g) ÷ fiber slurry amount before dehydration (g) × 100
Then, by using the sludge concentration and fiber slurry concentration calculated above, the amount of dry sludge contained in the sludge and the amount of dry fiber contained in the fiber slurry are calculated, whereby the ratio of fibers to the sludge used ( Dry weight ratio).
Fiber dry weight ratio (%) = dry fiber amount (g) ÷ dry sludge amount (g) × 100

  It is preferable that the sludge contains a substance having a positive charge. Positively charged substances include: aluminum sulfate, ferrous chloride, ferric chloride, ferrous sulfate, ferric sulfate, aluminum chloride, calcium chloride, polyaluminum chloride, polyferric sulfate, polydiallyldimethyl Examples thereof include inorganic salts and organic compounds such as ammonium chloride, polyamine, melamic acid colloid, and dicyandiamide. The positively charged substance may be a substance containing the same ions as those generated when the above-described inorganic salt or the like is dissolved in sludge. For example, a substance that dissolves in water and supplies aluminum ions or iron ions is supplied. It may be a substance.

(fiber)
Examples of the charged fiber that can be used in the present invention include wood pulp, cotton, hemp, waste paper pulp, and non-wood pulp. In addition, synthetic fibers such as polypropylene having a charge can be used. Furthermore, as a pulp, the fiber collect | recovered from the paper pulp manufacturing factory and the sludge containing many fiber parts can also be used.
It is preferable that the pulp has a charge. When a pulp having no charge is used, a pulp having a charged substance fixed or adsorbed on the pulp may be used. The fiber having a charge has a large specific surface area and is preferably a flexible material. The charge possessed by the fiber may be anionic or cationic. Further, the amount of electric charge in the fiber is not particularly limited.

  In the present invention, it is preferable to use wood-derived pulp as the charged fiber. The fiber derived from wood pulp has an anionic charge because it has a carboxyl group derived from hemicellulose. Moreover, since the structure of the fiber is a polymerized polysaccharide with a complex structure, it has a large specific surface area and is flexible so that the moisture content of the dehydrated cake can be effectively reduced. Furthermore, when wood pulp is used, fibers and sludge are intertwined well, so that a dense flock is formed, and it is possible to improve the separation between water and sludge before dehydrating with a dehydrator. In addition, wood pulp is preferable because it is a natural product and can be supplied continuously and is inexpensive.

  When wood pulp is used, the wood pulp may be pretreated. For example, the specific surface area can be increased by beating in the pretreatment step. In addition, the wood pulp is subjected to an oxidation treatment using a known oxidation method such as ozone, chlorine, chlorine dioxide, persulfuric acid, hypochlorous acid, or hydrogen peroxide, or a TEMPO oxidation method or Fenton oxidation method. It can also be used after increasing the amount of anionic residues in the wood pulp. Further, an anionic compound and / or a cationic compound may be used after being fixed or adsorbed on wood pulp.

  In the pretreatment step, when beating is performed, the pulp freeness is preferably 750 ml or less, preferably 650 ml or less, and more preferably 550 ml or less. The freeness is a freeness value measured by a Canadian standard freeness tester in accordance with JIS-P8121, after the sample was disaggregated in accordance with JIS-P8220. . By setting the freeness of the pulp within the above range, the specific surface area of the pulp can be increased and the flexibility can be increased, so that the moisture content of the dehydrated cake can be effectively reduced.

  Examples of the wood pulp include pulp derived from conifers (NKP) and pulp derived from hardwoods (LKP). Among them, it is preferable to use hardwood derived pulp (LKP). Since hardwood-derived pulp (LKP) has a large specific surface area and is a flexible material, the moisture content of the dehydrated cake can be more effectively reduced.

(Flocculant)
The charged flocculant used in the present invention is preferably at least one selected from a cationic flocculant, an anionic flocculant, and a nonionic flocculant, and is selected from a cationic flocculant and an anionic flocculant. It is more preferable that it is at least one kind. At least one flocculant may be added to the sludge, but two or more flocculants may be added. Specifically, it is preferable to add both a cationic flocculant and an anionic flocculant. The order of addition is not particularly limited, and after adding the anionic flocculant, the cationic flocculant may be added, or after adding the cationic flocculant, the anionic flocculant may be added.

Examples of the flocculant that can be used in the present invention include anionic polyacrylamide, cationic polyacrylamide, nonionic polyacrylamide, anionic sodium polyacrylate, cationic polyacrylic acid alkyl ester, and cationic polymethacrylic acid. Examples include alkyl esters, cationic polyamines, cationic poly (diallyldimethylammonium chloride), cationic dicyandiamide, cationic amino condensates, anionic sodium alginate, anionic carboxymethylcellulose, and nonionic causticized starch. The flocculant can be used regardless of its molecular weight or the amount of functional groups that provide the main properties. Moreover, it can be used regardless of the shape such as linear or branched.
In the present invention, inorganic salts can also be used as the flocculant. Examples of inorganic salts include aluminum sulfate, sodium aluminate, polyaluminum chloride, ferrous sulfate, ferric chloride, ferric sulfate, chlorinated coppers, and the like.

  Only one type of flocculant can be used, or a plurality of types can be used. In addition, auxiliary agents such as diatomaceous earth and activated silica, pH adjusters such as sulfuric acid, hydrochloric acid and sodium hydroxide, oxidizing and reducing agents such as manganate, hypochlorite and ferrous sulfate, and coagulants It can also be used. Selection of the coagulant, auxiliary agent, and charged fiber and determination of the amount added are carried out in consideration of dewaterability by performing a jar test or a dehydration test.

(Sludge dewatering equipment)
The present invention also relates to a sludge dewatering device. The sludge dewatering device of the present invention comprises means for adding a coagulant having a charge to the sludge contained in the waste water, and means for adding a fiber having a charge to the sludge containing the coagulant. Here, the means for adding the charged fiber is a means for adding so that the ratio of the charged fiber is 3% by weight or more with respect to the sludge. The means for adding the charged fiber is preferably a means for adding so that the ratio of the fiber to the sludge is 5 to 70% by weight, more preferably more than 10% by weight and 70% by weight. Hereinafter, it is a means to add so that it may become 15 weight%-70 weight% more preferably.

  As shown in FIG. 1, the sludge dewatering device of the present invention includes a coagulation tank 10, a coagulant storage tank 20, a sludge volume reduction tank 15, a fiber storage tank 30, and a dehydrator 40. Preferably it is. The agglomeration tank 10 is preferably provided with a stirrer 12, and the sludge volume reducing tank 15 is preferably provided with a stirrer 17. A coagulant storage tank 20 is connected to the coagulation tank 10, and the coagulant is added from the coagulant storage tank 20 to the sludge volume reduction tank 15. Further, a fiber storage tank 30 is connected to the sludge volume reducing tank 15, and fibers are added from the fiber storage tank 30 to the sludge volume reducing tank 15.

  The sludge dewatering apparatus of the present invention preferably further comprises means for concentrating the sludge containing the flocculant. The means for concentrating is preferably a coagulation sedimentation device, a pressure flotation device, or a centrifuge. By concentrating the sludge containing the flocculant using such an apparatus, it can be efficiently mixed with the charged fibers in the subsequent step.

  The sludge mixed with the flocculant and the fibers is dehydrated by the dehydrator 40. Examples of the dehydrator 40 include a screw press, a filter press, a centrifugal dehydrator, a belt press, and an electroosmotic dehydrator.

  In addition, the sludge dewatering apparatus of the present invention preferably further includes a flocculant storage tank, a coagulation sedimentation tank, a biological treatment membrane, an activated sludge treatment tank, and the like.

  The features of the present invention will be described more specifically with reference to examples and comparative examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

Example 1
An anionic flocculant was added to 500 g of sludge discharged from a paper mill and containing 300 ppm of aluminum sulfate so as to be 100 ppm. After the addition, the mixture was stirred at 120 rpm for 1 minute, and further stirred at 40 rpm for 5 minutes. A cationic flocculant was added to 100 ppm, stirred at 120 rpm for 1 minute, and further stirred at 40 rpm for 4 minutes to form a floc. Thereafter, 3% by weight of the fiber (with respect to the sludge dry weight ratio) was added, stirred at 120 rpm for 1 minute, and further stirred at 40 rpm for 4 minutes to form a floc. The obtained flock was dehydrated with a screw press to obtain a dehydrated cake.
In addition, the addition method (1)-(4) of the coagulant | flocculant and fiber in Table 1 represents an addition order.

(Example 2)
An anionic flocculant was added to 500 g of sludge discharged from a food factory and containing 100 ppm of ferric chloride so as to be 100 ppm. After the addition, the mixture was stirred at 120 rpm for 1 minute, and further stirred at 40 rpm for 5 minutes. A cationic flocculant was added to 100 ppm, stirred at 120 rpm for 1 minute, and further stirred at 40 rpm for 4 minutes to form a floc. Thereafter, 5% by weight of the fiber (based on the sludge dry weight ratio) was added, and the mixture was stirred at 120 rpm for 1 minute, and further stirred at 40 rpm for 4 minutes to form a floc. The obtained flock was dehydrated with a screw press to obtain a dehydrated cake.

(Example 3)
An anionic flocculant was added to 500 g of sludge discharged from a sewage treatment facility and containing 200 ppm of polyaluminum chloride so as to be 100 ppm. After the addition, the mixture was stirred at 120 rpm for 1 minute, and further stirred at 40 rpm for 5 minutes. A cationic flocculant was added to 100 ppm, stirred at 120 rpm for 1 minute, and further stirred at 40 rpm for 4 minutes to form a floc. Thereafter, 10% by weight of the fiber (to the sludge dry weight ratio) was added, stirred at 120 rpm for 1 minute, and further stirred at 40 rpm for 4 minutes to form a floc. The obtained flock was dehydrated with a screw press to obtain a dehydrated cake.

Example 4
An anionic flocculant was added to 500 g of sludge discharged from a food factory and containing 300 ppm of aluminum sulfate so as to be 100 ppm. After the addition, the mixture was stirred at 120 rpm for 1 minute, and further stirred at 40 rpm for 5 minutes. A cationic flocculant was added to 100 ppm, stirred at 120 rpm for 1 minute, and further stirred at 40 rpm for 4 minutes to form a floc. Thereafter, 30% by weight of the fiber (based on the sludge dry weight ratio) was added, and the mixture was stirred at 120 rpm for 1 minute and further stirred at 40 rpm for 4 minutes to form a floc. The obtained flock was dehydrated with a screw press to obtain a dehydrated cake.

(Example 5)
An anionic flocculant was added to 500 g of sludge discharged from a sewage treatment facility and containing 100 ppm of ferric chloride so as to be 100 ppm. After the addition, the mixture was stirred at 120 rpm for 1 minute, and further stirred at 40 rpm for 5 minutes. A cationic flocculant was added to 100 ppm, stirred at 120 rpm for 1 minute, and further stirred at 40 rpm for 4 minutes to form a floc. Thereafter, 50% by weight of the fiber (to the sludge dry weight ratio) was added, stirred at 120 rpm for 1 minute, and further stirred at 40 rpm for 4 minutes to form a floc. The obtained flock was dehydrated with a screw press to obtain a dehydrated cake.

(Example 6)
An anionic flocculant was added to 500 g of sludge discharged from a paper mill and containing 100 ppm of ferric chloride so as to be 100 ppm. After the addition, the mixture was stirred at 120 rpm for 1 minute, and further stirred at 40 rpm for 5 minutes. A cationic flocculant was added to 100 ppm, and the mixture was stirred at 120 rpm for 1 minute, and further stirred at 40 rpm for 4 minutes to form flocs, and sludge was precipitated. The precipitated sludge was extracted and concentrated on a rotary screen. Fibers were added to the concentrated sludge at 5 wt% (ratio to sludge dry weight) to form flocs. The obtained flock was dehydrated with a screw press to obtain a dehydrated cake.

(Comparative Example 1)
The sludge discharged from the food factory was 10% by weight (ratio of sludge dry weight) to 500 g of sludge containing 200 ppm of aluminum sulfate. The mixture was stirred at 120 rpm for 1 minute, further stirred at 40 rpm for 4 minutes, and an anionic flocculant was added to 100 ppm. After the addition, the mixture was stirred at 120 rpm for 1 minute, and further stirred at 40 rpm for 5 minutes. A cationic flocculant was added to 100 ppm, stirred at 120 rpm for 1 minute, and further stirred at 40 rpm for 4 minutes to form a floc. The obtained flock was dehydrated with a screw press to obtain a dehydrated cake.

(Comparative Example 2)
An anionic flocculant was added to 500 g of sludge discharged from a sewage treatment facility and containing 100 ppm of polyaluminum chloride so as to be 100 ppm. After the addition, the mixture was stirred at 120 rpm for 1 minute, further stirred at 40 rpm for 5 minutes, a cationic flocculant was added to 100 ppm, stirred at 120 rpm for 1 minute, and further stirred at 40 rpm for 4 minutes to form a floc. . Thereafter, 1% by weight of the fiber (with respect to the sludge dry weight ratio) was added, stirred at 120 rpm for 1 minute, and further stirred at 40 rpm for 4 minutes to form a floc. The obtained flock was dehydrated with a screw press to obtain a dehydrated cake.

(Evaluation)
(Dehydrated cake moisture content)
The weight of the obtained dehydrated cake was measured. The obtained dehydrated cake was dried for 24 hours in a dryer set at 105 ° C. The moisture content of the dehydrated cake was calculated according to the following formula from the weight of the dehydrated cake before and after drying.
Moisture content of dehydrated cake (% by weight) = (weight after dehydration-weight after drying) ÷ (weight after dehydration)
× 100

(Dehydrated cake weight reduction rate)
The dehydrating cake weight reduction rate was calculated by the following formula.
Weight reduction rate of dehydrated cake (%)
= (Weight of dehydrated cake after dehydration without adding fiber-Weight of dehydrated cake after dehydration with added fiber) / Weight of dehydrated cake after dehydration with added fiber × 100

In Examples 1-6 compared with a comparative example, it turns out that the moisture content of a dewatering cake is reduced. In particular, when the fiber addition rate is 30% by weight or more, the moisture content of the dehydrated cake is reduced.
Furthermore, in an Example, it turns out that the dehydration cake weight reduction rate is also high. By reducing the sludge weight after dehydration, it is possible to reduce the processing cost when the sludge is landfilled as industrial waste. In addition, since the sludge moisture after dehydration is reduced, self-combustion is possible when the sludge is incinerated, and auxiliary fuel costs for sludge combustion can be reduced. In addition, since self-combustion is possible, sludge after dehydration can be used as fuel.

DESCRIPTION OF SYMBOLS 10 Coagulation tank 12 Agitation machine 15 Sludge volume reduction tank 17 Agitation machine 20 Coagulant storage tank 30 Fiber storage tank 40 Dehydrator

Claims (10)

Adding a flocculant having electric charge to the sludge contained in the waste water;
Adding a charged fiber after the step of adding the charged flocculant,
The sludge dewatering method, wherein the fibers having electric charge are added to the sludge so that the dry weight ratio is 3% by weight or more.   The sludge dewatering method according to claim 1, wherein the fibers having electric charges are added to the sludge so as to have a dry weight ratio of 5 to 70 wt%.   The sludge dewatering method according to claim 1 or 2, wherein the fibers having electric charges are added to the sludge so that the dry weight ratio is more than 10 wt% and 70 wt% or less. After the step of adding the flocculant having the charge, further comprising a concentration treatment step,
The method for dewatering a sludge of a substrate according to any one of claims 1 to 3, further comprising a step of adding a fiber having electric charge after the concentration treatment step.   The sludge dewatering method according to any one of claims 1 to 4, wherein the fibers having electric charges are wood-derived pulp.   The sludge dewatering method according to any one of claims 1 to 5, wherein the fiber having electric charge is a hardwood-derived pulp.   The method for dewatering sludge according to any one of claims 1 to 6, wherein the flocculant is at least one selected from a cationic flocculant and an anionic flocculant. Means for adding a flocculant having electric charge to the sludge contained in the waste water;
Means for adding a fiber having a charge to the sludge containing the flocculant,
The means for adding the charged fibers is a means for adding so that the proportion of the charged fibers is 3% by weight or more in dry weight ratio with respect to the sludge. apparatus.   9. The sludge according to claim 8, wherein the means for adding the charged fiber is a means for adding so that a ratio of the charged fiber is 5 to 70% by weight with respect to the sludge in a dry weight ratio. Dehydration equipment.   The sludge dewatering device according to claim 8 or 9, further comprising means for concentrating the sludge containing the flocculant.

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