JP6600574B2 - Polymer flocculant, method and apparatus for dewatering sludge using polymer flocculant - Google Patents

Description

  The present invention relates to a polymer flocculant added to sludge, and in particular, a polymer flocculant added to this sludge for sludge flocculation treatment after biological treatment of organic waste, The present invention relates to a dewatering method and a dewatering device for sludge used.

  When organic matter-containing wastewater is purified at a human waste treatment plant or a sewage treatment plant, organic sludge is generated along with the purified treated water. The organic sludge is subjected to a coagulation treatment in which a coagulant is added, and then subjected to a dehydration treatment using a dehydrator or the like to obtain a dehydrated cake.

  Conventionally, biogas containing methane gas generated by methane fermentation treatment of food waste has been collected, and solid matter in the digested liquid after biogas recovery is dehydrated to form a dehydrated cake.

  The energy of methane gas in the collected biogas is used for power generation and incineration of dehydrated cake, which will be described later.

  The dehydrated cake is made into cement or landfill material, or disposed of by incineration, but the water content of the dehydrated cake is reduced to reduce the weight and volume of the dehydrated cake regardless of which method is used. Is required to be reduced as much as possible.

Some of the organic sludge produced by the purification treatment of waste water is difficult to dehydrate, and there is a need to reduce the moisture content of the dehydrated cake derived from such difficult to dehydrate organic sludge.
In particular, digested sludge that has undergone anaerobic digestion to surplus sludge generated at sludge treatment facilities such as sewage treatment plants generally has a high negative colloidal value, and a large amount of flocculant needs to be added in order to agglomerate. It becomes. This is also true for solids in digestive juice after methane fermentation of food waste.

  In addition, suspended solid SS (Suspended Solids) in the digested sludge and the solid matter in the digested liquid after the methane fermentation treatment has a small particle size, and it is difficult to form a strong floc because of its small fiber content. There is a problem that the moisture content of the dehydrated cake is difficult to decrease.

  In addition, dehydrated cakes based on digested sludge and solids in digested liquid after methane fermentation treatment have poor peelability of the dehydrated cake from the dewatering means such as a belt press during the dehydration process, which causes a decrease in workability of the dewatering process. ing.

  Then, in order to reduce the moisture content of the dewatered cake, Patent Document 1 and Patent Document 2 propose a method for dewatering sewage digested sludge.

  Specifically, Patent Document 1 discloses a digested sludge dewatering method in which an inorganic flocculant and an acrylate-based cationic polymer flocculant are added to digested sludge to form a floc floc and then dewatered. According to this, the addition of an acrylate cationic polymer flocculant as a cationic flocculant to the digested sludge promotes the coarsening of flocs, while reducing the amount of inorganic flocculant added than before, dehydrated cake The water content is reduced.

  In Patent Document 2, a cationic polymer is added to digested sludge to perform a coagulation treatment, the coagulated sludge is subjected to gravity dehydration, an inorganic coagulant is added to the gravity dehydrated sludge, and the amphoteric polymer is added to the conditioned sludge. A method for dewatering digested sludge that is added and dewatered is disclosed. According to this, digested sludge is concentrated by gravity dewatering after addition of a cationic polymer to the digested sludge, and the inorganic flocculant is added to the concentrated digested sludge. By adding, problems that occur when the inorganic flocculant is first added to the digested sludge, such as generation of carbon dioxide gas, consumption of the inorganic flocculant due to the reaction between the liquid in the sludge and the inorganic flocculant, are avoided.

  Patent Document 3 discloses a method of coagulating sludge characterized by the method of mixing the sludge and the polymer flocculant. Specifically, the sludge is mixed with the first polymer flocculant solution and stirred at a high speed. In addition, the second polymer flocculant solution is further mixed and stirred at a low speed to form an agglomeration floc.

  According to this, the first polymer flocculant is added to the digested sludge and stirred at a high speed, and then the second polymer flocculant is added and stirred at a low speed, so that The polymer flocculant spreads to the details of the sludge, and the second polymer flocculant gently comes into contact with the sludge mixed with the first polymer flocculant by subsequent low-speed stirring, and the flocculent floc grows.

  That is, uniform mixing of the polymer flocculant and sludge and growth of the flocculent flocs are realized, and the moisture content of the dewatered cake obtained after dehydration can be reduced while suppressing the amount of flocculant added.

JP-A-7-214100 Japanese Patent Laid-Open No. 9-024400 International Publication No. 2012/108312

  However, according to the method for dewatering digested sludge of Patent Document 1, although the amount of inorganic flocculant added is reduced compared to the conventional method, the amount of the polymer flocculant is more than 10 times that of the coagulant for digestion sludge. It is essential to add an inorganic flocculant at the beginning of the flocculation treatment, and there is still a problem that a large amount of the flocculant is required to reduce the moisture content of the dehydrated cake.

  Further, according to Patent Document 2, it is necessary to add an inorganic flocculant in an amount more than 10 times that of the cationic polymer in order to neutralize the charge of sludge particles and form a strong floc. is there.

  Patent Document 3 is an invention according to the applicant's patent application of the present application. According to this, there is no need to add an inorganic flocculant, and the water content of the dehydrated cake is reduced while suppressing the flocculant addition amount. However, it only discloses a method in which the same type of polymer flocculant is added in two portions, and does not disclose any details about the physical properties of the dehydrated cake.

  The present invention has been made in view of the above-described conventional problems. The object of the present invention is to reduce the moisture content of the dehydrated cake while reducing the amount of addition as a whole, and to peel the dehydrated cake. A polymer flocculant for coagulating sludge after biological treatment of organic waste, which can improve the property, a sludge dewatering method using the polymer flocculant, and an apparatus used for the sludge dewatering method There is.

In order to achieve the above object, the invention described in claim 1 is a polymer flocculant added to sludge for agglomeration of sludge after biological treatment of organic waste, comprising polyamidine, amino the mass ratio of the polymer containing an alkyl (meth) acrylate, 10: 90 to 90: mixture der ranges from 10 is, the sludge after the biological treatment of the organic waste, methane fermentation of food waste It is a digestive juice after processing .

  According to this configuration, when the polymer flocculant is added to the sludge after biological treatment of organic waste under a predetermined stirring condition, the polymer flocculant is spread to the inside of the aggregate than before. Therefore, the pores that serve as a passage for water of the obtained aggregates are also developed, and the dehydrating property is also improved.

  Therefore, it is possible to reduce the moisture content of the dehydrated cake obtained while reducing the amount of the flocculant added as a whole. Moreover, the peelability of the obtained dehydrated cake is also improved.

  Preferred embodiments of the polymer flocculant according to the present invention are as follows.

(1) The polymer containing aminoalkyl (meth) acrylate is selected from the group consisting of dimethylaminoethyl methacrylate homopolymer, acrylamide / dimethylaminoethyl acrylate copolymer, and acrylamide / acrylic acid / dimethylaminoethyl acrylate copolymer. At least one or more .

In addition, the above object is to add a polymer flocculant to the sludge after biological treatment of organic waste, to obtain an agglomerate by stirring the sludge to which the polymer flocculant is added, and to dehydrate the agglomerate. in the dehydration method of sludge, the sludge after the biological treatment of the organic waste is a digestive liquid after the methane fermentation treatment of food waste, it said polymeric flocculant is a high of claim 1 or 2 The molecular flocculant is added, and the addition of the polymer flocculant and the stirring are performed by adding a part of the necessary amount of the polymer flocculant to the sludge after the biological treatment, and performing the first stirring. This is also achieved by a sludge dewatering method characterized by adding the remainder of the necessary addition amount after stirring and performing the second stirring at a slower rate than the first stirring.

  According to this configuration, it becomes possible to spread the polymer flocculant added to the sludge after biological treatment of organic waste to the inside of the agglomerate than before. The pores that serve as escape passages also develop, and the dehydrating property is also good.

  Therefore, it is possible to reduce the moisture content of the dehydrated cake obtained while reducing the amount of the flocculant added as a whole. Moreover, the peelability of the obtained dehydrated cake is also improved.

  Furthermore, the remainder of the required addition amount of the polymer flocculant is added, and the second stirring is performed at a slower speed than the first stirring, so that the aggregation of the sludge particles proceeds and the size of the aggregation suitable for dehydration is increased. Things are generated. At this time, since the polymer flocculant of the present invention is used, the polymer flocculant spreads to the inside of the agglomerate, and the pores that serve as a passage for water are well developed. It has become.

  Therefore, it is possible to reduce the moisture content of the dehydrated cake obtained while reducing the amount of the flocculant added as a whole. Moreover, the peelability of the obtained dehydrated cake is also improved.

  Preferred embodiments of the sludge dewatering method according to the present invention are as follows.

(1) The ratio of a part of the required addition amount of the polymer flocculant and the remainder thereof is in the range of 10:90 to 90:10.
(2) 1st stirring is 200 rpm or more, and 2nd stirring is less than 200 rpm.
(3) It has the concentration process which concentrates an aggregate between 2nd stirring and a spin-drying | dehydration process, and includes adding an inorganic flocculant in the concentration process or after a post-concentration process and before a dehydration process.

  As a result, the addition of the inorganic flocculant forms a stronger floc, and the inorganic flocculant added by reacting the separation liquid and the inorganic flocculant present together with the sludge aggregates is not consumed. It is also possible to reduce the amount of flocculant added.

Further, the object is to provide a first flocculant addition means for adding a part of the required amount of the polymer flocculant according to claim 1 or 2 to the sludge after biological treatment of organic waste. First stirring means capable of stirring at a speed necessary for dispersing a part of the polymer flocculant in the sludge to which the part of the polymer flocculant is added by the first flocculant addition means. And a second flocculant addition means for adding the remainder of the required amount of the polymer flocculant to the dispersed sludge in which a part of the polymer flocculant is dispersed by the stirring, and the sludge aggregate In order to obtain the second aggregating agent, the second agitation agent capable of agitating the dispersed sludge to which the remainder of the polymer flocculant has been added by the second aggregating agent addition means at a slower rate than the first agitation agent; Dehydrating means for dehydrating the agglomerates obtained by stirring of the stirring means, and The ratio between the part of the required amount of molecular flocculant and the remainder, 10: 90 to 90: 10 range der of is, the sludge after the biological treatment of the organic waste, methane fermentation of food waste It is also achieved by a sludge dewatering device characterized by being a later digestive juice .

  According to this configuration, it becomes possible to spread the polymer flocculant added to the sludge after biological treatment of organic waste to the inside of the agglomerate than before. The pores that serve as escape passages also develop, and the dehydrating property is also good.

  Therefore, it is possible to reduce the moisture content of the dehydrated cake obtained while reducing the amount of the flocculant added as a whole. Moreover, the peelability of the obtained dehydrated cake is also improved.

  According to the present invention, it becomes possible to spread the polymer flocculant added to the sludge after biological treatment of organic waste to the inside of the agglomerate than before. The pores that serve as escape passages also develop, and the dehydrating property is also good.

  Therefore, it is possible to reduce the moisture content of the dehydrated cake obtained while reducing the amount of the flocculant added as a whole. Therefore, the transportation cost to the landfill of the dehydrated cake and the incineration cost can be saved. Further, by improving the peelability of the obtained dehydrated cake, the dewatered cake is prevented from being blocked in the dewatering means, and the maintenance interval of the dewatering means can be increased.

1 is a schematic diagram of a sludge dewatering device 10 according to a first embodiment of the present invention. It is a schematic diagram of the sludge dehydration apparatus 50 which concerns on 2nd Embodiment of this invention.

  Next, embodiments of the present invention will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 is a schematic diagram showing a sludge dewatering device 10 according to the present embodiment. As shown in FIG. 1, the sludge dewatering device 10 is used to add a part of the required addition amount of the polymer flocculant 2 to the first stirring tank 12 into which the sludge 1 is charged and the first stirring tank 12. First flocculant addition means 14, second agitation tank 16 located downstream of the first agitation tank, and second for adding the remainder of the required addition amount of polymer flocculant 2 to the second agitation tank 16. The flocculant adding means 17 and the dehydrating means 18 located downstream of the second stirring tank 16.

  Sludge 1 is sludge after biological treatment of organic waste. Organic waste refers to waste containing organic matter, and the property may be liquid or solid. In the case of a solid material, it is preferably used for biological treatment after it is mixed with a liquid such as water and becomes flowable. Examples of organic waste include waste water from food factories, sewage, food waste (such as food waste), and livestock waste.

  Biological treatment includes both aerobic treatment and anaerobic treatment. As the aerobic treatment, a conventionally known aerobic biological treatment can be applied. Specifically, an organic waste is received in a tank and aerated while being stirred. More specifically, the floating biological treatment method (activated sludge method) and the biofilm treatment method (rotating disc method, aerobic filter bed method, fluidized bed method) used in sewage treatment can be mentioned.

  Anaerobic treatment is a treatment that decomposes organic matter into methane gas or carbon dioxide gas by the metabolic action of anaerobic bacteria that grow in an anaerobic environment. Therefore, examples of anaerobic bacteria include methanogenic bacteria. More specifically, the anaerobic treatment includes treatment by an anaerobic fixed bed method, anaerobic fluidized bed method, UASB method, EGSB method and the like.

  The polymer flocculant 2 is a mixture of polyamidine and a polymer mainly composed of aminoalkyl (meth) acrylate.

  The sludge 1 that has been subjected to methane fermentation by a methanogen as an anaerobic treatment generally has a CST of 7,000 sec or more, and the present invention is particularly effective for sludge having such a CST.

  The required addition amount of the polymer flocculant 2 refers to the addition amount of the polymer flocculant 2 necessary for generating the agglomerate 4 for performing an appropriate dehydration treatment from the sludge 1. It can represent with the percentage of the solid content (g) of the polymer flocculent 2 with respect to solid content (g).

  The required amount of the polymer flocculant 2 is in the range of 1.0% to 5.0%, preferably in the range of 2.0% to 3.0%.

The polyamidine used in the present invention is obtained by copolymerizing N-vinylformamide and acrylonitrile, hydrolyzing the obtained copolymer under hydrochloric acid acidity, and then performing a heat treatment, whereby a primary amino group and a cyano group on the inner chain of the molecule are obtained. Is cyclized to form an amidine ring.

It is a polymer which has a repeating unit represented by these. The polyamidine may have other repeating units other than the repeating unit (I), but the content of the repeating unit (I) is 50 mol% or more, preferably 80 mol% or more, and may be 100 mol%. .

  The polymer mainly composed of aminoalkyl (meth) acrylate is a homopolymer of aminoalkyl (meth) acrylate cationic monomer or aminoalkyl (meth) acrylate cationic monomer and anionic monomer or nonion It is a copolymer with a functional monomer.

  Examples of aminoalkyl (meth) acrylate cationic monomers include dialkylaminoalkyl (meth) acrylates such as dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, and diethylamino-2-hydroxypropyl (meth) acrylate. Quaternary salts such as alkyl chloride adducts such as methyl chloride adducts of dialkylaminoalkyl (meth) acrylates and aryl halide adducts such as benzyl chloride; N, N -Hydrochloric acid salts such as dialkyl (meth) acrylamides such as dimethyl (meth) acrylamide and tertiary salts such as sulfates; alkyl halide adducts such as methyl chloride adducts of dialkyl (meth) acrylamides and benzyl chloride adducts, etc. Such as aryl halide adducts Include the grade salt.

  Examples of nonionic monomers include (meth) acrylamide, styrene, acrylonitrile, vinyl acetate, alkyl (meth) acrylate, and the like. Among these, (meth) acrylamide is preferable.

  Examples of anionic monomers include (meth) acrylic acid and alkali metal salts or ammonium salts such as sodium salts thereof; maleic acid; acrylamide alkylalkane sulfonic acids such as acrylamide-2-methylpropanesulfonic acid and alkali metal salts thereof; An ammonium salt etc. are mentioned.

  Any of these monomers can be used alone or in combination of two or more.

  The polymerization method of the polymer is not particularly limited, and examples thereof include precipitation polymerization, bulk polymerization, dispersion polymerization, and aqueous solution polymerization.

  In addition to the polymer, a solid acid may be used for the purpose of improving the solubility and improving the storage stability of the solution. Examples of the solid acid include sulfamic acid and acidic sodium sulfite.

  In the polymer flocculant 2, the mass ratio of the polymer mainly composed of polyamidine and aminoalkyl (meth) acrylate is 10:90 to 90:10. In addition, this numerical value is a mass ratio when the total amount of both is 100 mass%.

  If the mass ratio of the polyamidine is less than 10% by mass, the effect of reducing the water content of the dehydrated cake 38, which will be described later, cannot be sufficiently obtained, and if it exceeds 90% by mass, the polymer flocculant 2 is necessary in the second stirring tank 16 described later. Aggregate growth after addition of the remainder of the addition amount becomes insufficient, and a strong floc that can withstand pressing in the dehydrating means 36 is not formed.

  In the above mass ratio range, the mass ratio between the polyamidine and the polymer mainly composed of aminoalkyl (meth) acrylate can be arbitrarily adjusted according to the properties of the sludge 1 and the dehydrating means 36 used.

  The polymer flocculant 2 in the present invention is used as an aqueous solution dissolved in water. The concentration of the aqueous solution is not particularly limited but is preferably 0.05 to 1.5%.

  The first agitation tank 12 has a first agitation means 20 for agitating the solution in the tank and an injection part for the polymer flocculant 2.

  The first stirring means 20 may be anything as long as it can stir the sludge 1 in the tank. In the present embodiment, the impeller (stirring) is mounted on the stirring shaft rotated by the motor. A wing attached) is used.

  The polymer flocculant 2 is stored in the polymer flocculant storage tank 22 in a liquid state. A part of the required addition amount of the polymer flocculant 2 is added to the first stirring tank 12 via the path 24. A pump 26 is provided in the path 24, and by controlling the driving of the pump 26, a part of the required amount of the polymer flocculant 2 added to the first stirring tank 12 is controlled.

  Therefore, the first flocculant adding means 14 is constituted by the path 24 and the pump 26.

  The second agitation tank 16 has a second agitation means 28 for agitating the solution in the tank, and an injection part for the polymer flocculant 2.

  In the present embodiment, the second stirring means 28, like the first stirring means 20, has an impeller (stirring blade) attached to a stirring shaft rotated by a motor.

  The remainder of the required amount of the polymer flocculant 2 is added from the polymer flocculant storage tank 22 to the second agitation tank 16 via the path 30. A pump 32 is provided in the path 30, and the remaining amount of the necessary amount of the polymer flocculant 2 added to the second stirring tank 16 is controlled by controlling the driving of the pump 32. That is, the second flocculant adding means 17 is constituted by the path 30 and the pump 32.

  The mixture 34 of the aggregate 4 and the separated liquid 5 generated through the stirring in the first stirring tank 12 and the stirring in the second stirring tank 16 is sent to the downstream dehydrating means 36.

  The dehydrating unit 36 is a unit that removes the separation liquid 5 from the mixture 34 and dehydrates the aggregate from the aggregate. Specific examples include conventionally known dehydrators such as a belt press dehydrator, a screw press dehydrator, a centrifugal dehydrator, and a filter press dehydrator. Among these, it is preferable to use a belt press type dehydrator or a screw press type dehydrator.

  After the dehydration process, the dehydrated cake 38 and the liquid part 40 are discharged from the dehydrating means 36, respectively.

  Next, a sludge dewatering method using the sludge dewatering apparatus 10 will be described below.

[Partial addition of required amount of polymer flocculant and first stirring step]
The sludge 1 after biological treatment of organic waste is put into the first stirring tank 12. A part of the required addition amount of the polymer flocculant 2 is further added to the first stirring tank 12. The part of the required addition amount of the polymer flocculant 2 means that the mass ratio of this part and the remainder of the required addition amount of the polymer flocculant 2 added to the second stirring tank 16 is 10:90 to 90. : An amount in the range of 10, preferably an amount in the range of 20:80 to 80:20. In addition, this numerical value is a mass ratio when the total amount of both, that is, the required addition amount of the polymer flocculant 2 is 100% by mass.

  If the mass ratio of the part of the polymer flocculant 2 added to the first stirring tank 12 is less than 10% by mass, the flocculant is insufficient and the aggregation is insufficient, and the polymer flocculant is added to the second stirring tank 16. If the mass ratio of the remainder of the polymer flocculant 2 exceeds 90% by mass, flocs caused by the aggregates generated in the second stirring tank 16 are likely to become enormous.

  Further, when the mass ratio of the part of the polymer flocculant 2 added to the first stirring tank 12 exceeds 90% by mass, the remaining part of the polymer flocculant 2 added to the second stirring tank 16 Is less than 10% by mass, and a strong floc that can withstand physical dehydration by the dehydrating means 36 is not formed.

  The polymer flocculant 2 is added to the sludge 1 being stirred by the first stirring means 20. The stirring speed of the first stirring means 20, that is, the rotation speed of the impeller is such that a part of the required addition amount of the polymer flocculant 2 added by the first flocculant addition means 14 is dispersed in the sludge 1 in the tank. Any rotational speed may be used as long as it is necessary to cause the sludge to react sufficiently with the sludge 1 and the polymer flocculant 2 by agitation at a high speed to form fine sludge particles. Preferably it is 200 rpm or more, More preferably, it is 500 rpm or more.

  By the stirring by the first stirring means 20, the sludge 1 becomes the dispersed sludge 3 in which the above-mentioned part of the polymer flocculant 2 is dispersed, and the dispersed sludge 3 is sent to the second stirring tank 16 downstream (the polymer flocculant as described above). A part of the required addition amount and the first stirring step).

[Addition of remainder of necessary addition amount of polymer flocculant and second stirring step]
In the second agitation tank 16 into which the dispersed sludge 3 has flowed, the remainder of the required amount of the polymer flocculant 2 is added.

  The polymer flocculant 2 is added to the dispersed sludge 3 being stirred by the second stirring means 28. The stirring speed of the second stirring means 28, that is, the impeller rotation speed, may be any speed as long as it is necessary for separating the dispersed sludge 3 into the separation liquid and the aggregate. Specifically, the rotation speed is lower than the rotation speed of the impeller of the first stirring means 20, preferably 200 rpm or less, and particularly preferably in the range of 50 rpm to 150 rpm.

  By the stirring by the second stirring means 28, the dispersed sludge 3 becomes a mixture 34 of the aggregate 4 and the separation liquid 5, and the mixture 34 is sent to the downstream dewatering means 36 (the remainder of the necessary amount of the polymer flocculant added). And a second stirring step).

[Dehydration process]
The mixture 34 sent downstream of the second stirring tank 16 is subjected to a dehydration process by the dehydrating means 36.

  In the dehydrating means 36, the separation liquid 5 is physically removed, and the aggregate 4 is physically adhered to form an aggregate. Further, the water content in the agglomerates is further squeezed out by squeezing or the like to form a dehydrated cake 38, which is discharged from the dewatering means 36 via the path 42. The water extracted from the separation liquid 5 and the agglomerates removed in the dehydrating means 36 is discharged from the dehydrating means 36 via the path 44 as the liquid portion 40 (the above is the required amount of addition of the polymer flocculant). In the second stirring step).

  Therefore, according to the present embodiment, the first stirring tank 12 performs the first stirring at a speed faster than the second stirring, so that the sludge 1 and the added polymer flocculant 2 are added. Dispersion with a part of the amount becomes sufficient, and the viscosity of the sludge 1 is lowered. Moreover, the excessive growth of sludge particles is inhibited by agitation at a high speed, and fine sludge particles are obtained.

  Furthermore, in the second stirring tank 16, the remainder of the required addition amount of the polymer flocculant 2 is added, and the second stirring is performed at a speed slower than the first stirring, so that the aggregation of the sludge particles proceeds. Aggregate 4 having a size suitable for dehydration is produced. At this time, since the polymer flocculant 2 of the present invention is used, the polymer flocculant 2 reaches the inside of the agglomerate 4 and the pores from which water passes are well formed, so that the dehydrating property is good. Aggregate 4 is formed.

  Therefore, it is possible to reduce the moisture content of the dehydrated cake 38 obtained while reducing the amount of the flocculant added as a whole. Moreover, the peelability of the obtained dehydrated cake 38 is also improved.

  In the present embodiment, the dehydrating means 36 is provided immediately downstream of the second stirring tank 16, and the mixture produced by the [addition of the remainder of the required amount of the polymer flocculant and the second stirring step]. 34 is directly subjected to the [dehydration step], but is not limited to this, and may take another form.

(Second Embodiment)
Below, the dewatering apparatus 50 of the sludge which changed the structure downstream of the 2nd stirring tank 16 is demonstrated based on FIG. In FIG. 2, elements similar to those of the embodiment shown in FIG. 1 described above are denoted by the same reference numerals and description thereof is omitted. FIG. 2 is a schematic diagram of a sludge dewatering device 50 according to the present embodiment.

  As shown in FIG. 2, the sludge dewatering device 50 according to the present embodiment is a concentrating means 52 for concentrating the aggregates generated in the second stirring tank 16 between the second stirring tank 20 and the dewatering means 36. This is different from the sludge dewatering device 10 according to the first embodiment in that

  As the concentrating means 52, a known gravity dehydrator such as a rotary screen, an inclined screen, or a filter cloth traveling dehydrator can be used. Moreover, the concentration means 52 has an inorganic flocculant injection part. The inorganic flocculant 6 is stored in a liquid state in the inorganic flocculant storage tank 54. The inorganic flocculant 6 is added to the concentration means 52 via the path 56. A pump 58 is provided in the path 56, and the amount of the inorganic flocculant 6 added to the concentration means 52 is controlled by controlling the driving of the pump 58.

  As the inorganic flocculant 6, known ones such as ferric chloride, polyferric sulfate (polyiron), sulfuric acid band, polyaluminum chloride (PAC), and aluminum chloride can be used.

  The amount of the inorganic flocculant 6 added is expressed as a percentage of the solid amount (g) of the inorganic flocculant 6 with respect to the solid amount (g) of the SS of the sludge 1 and is preferably in the range of 1% to 5%, for example. Is in the range of 2% to 3%.

  Next, a sludge dewatering method using the sludge dewatering apparatus 50 according to the present embodiment will be described mainly with respect to steps different from those of the first embodiment.

  As in the first embodiment, the sludge 1 is supplied to [a part of the required amount of addition of the polymer flocculant and the first stirring step] in the first stirring tank 12 to become the dispersed sludge 3. Next, the dispersed sludge 3 is subjected to [addition of the remaining amount of polymer flocculant and second stirring step] in the second stirring tank 16, and the mixture 34 of the aggregate 4 and the separation liquid 5 Become. This mixture 34 is sent to the concentration means 52 downstream of the second stirring tank 16.

[Aggregate concentration step]
In the concentrating means 52, the separation liquid 5 in the mixture 34 is discharged according to gravity, and the discharged separation liquid 5 joins the liquid part 40 via the path 60. In addition, the inorganic flocculant 6 is added to the mixture 34 from the inorganic flocculant storage tank 54 via the path 56 at a midpoint of the concentration means 52. By the addition of the inorganic flocculant 6, the agglomerate 4 becomes a stronger floc and is sent to the downstream dewatering means 36 (hereinafter, agglomerate concentration step).

  Thereafter, the agglomerate 4 is supplied to the [dehydration step] in the dehydrating unit 36, and the dehydrated cake 36 and the liquid part 40 generated after the dehydrating step are discharged from the dehydrating unit 36, respectively.

  Therefore, according to the present embodiment, the inorganic flocculant 6 is added to the mixture 34 during concentration or the aggregate 4 after concentration in the concentrating means 52, so that the mixture 34 before concentration is added to the mixture 34 before concentration. Compared with the case where it is added, the proportion of the inorganic flocculant 6 consumed by reacting with the separation liquid 5 is reduced.

  Therefore, when the inorganic flocculant 6 is added, the amount of the inorganic flocculant 6 added can be reduced.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of invention. For example, in the above-described embodiment, the sludge 1 is mixed and stirred with a part of the required amount of the polymer flocculant 2 in the first stirring tank 12, but the first stirring tank 12 is not included. It is also possible. In that case, the sludge dewatering apparatus has a static mixer as the first stirring means in place of the first stirring tank 12, and a part of the required addition amount of the polymer flocculant 2 in the polymer flocculant storage tank 22 is: It is added to the sludge 1 at the upstream position of the static mixer.

  Further, when the sludge dewatering method of the present invention is carried out by a batch-type sludge dewatering device, it is possible to substitute the first stirring tank and the second stirring tank with one stirring tank, unlike the above embodiment. It is. In this case, the first stirring means and the second stirring means can also use one stirring means, and the addition of the polymer flocculant 2 from the polymer flocculant storage tank 22 to this one stirring tank is also performed in one system. This can be done via a route.

  Furthermore, in the said 2nd Embodiment, although the inorganic flocculant 6 is added in the middle position of the concentration means 52, it is not restricted to this, For example, a part of required addition amount of the polymer flocculant 2 is It can be added before or after the addition. Moreover, when the dehydrating means 36 has a concentrating part, it can add directly to the concentrated aggregate lump.

  In the above embodiment, the polymer flocculant 2 is added by the first flocculant addition means 14 and the second flocculant addition means 17, but may be performed manually.

  Hereinafter, the present invention will be described in more detail with reference to examples.

[Example 1]
Methane fermentation with methanogenic bacteria is performed on food waste as organic waste, and liquid sludge (pH 7.44, SS 27.5 g / L, VSS 61.2%, CST 12,500 sec, colloid charge −4. 28 meq / L) was obtained.

  (Note that SS is obtained by filtering particles contained in water with glass fiber filter paper or MF membrane filter paper having a pore diameter of 1 μm and expressing the particles in terms of dry matter weight (g / L). What is VSS (Volatile suspended solids)? , Refers to a substance that volatilizes when SS is ignited. After obtaining SS, the sample is ignited at 600 ± 25 ° C. for 30 minutes and the mass of the residue is measured.

  CST is an abbreviation for Capillary Suction Time (capillary suction time (unit: sec)), and the CST test is a test conducted for the purpose of judging the quality of sludge dehydration. A small amount of agglomerated sludge is added, and when the water in the sludge is sucked into the filter paper by the capillary phenomenon and expands in the circumferential direction, the time (sec) that passes between two concentric circles is measured. The CST value of the above liquid sludge is the sewage test method 2012 edition, first volume, page 728, volume 5, section 15. Obtained by measuring according to the items of the CST test.

  The colloid charge amount is obtained by centrifuging sludge, adding a toluidine blue indicator to the supernatant, and titrating with a polyvinyl potassium sulfate solution. )

  200 ml of this sludge is put into a 500 ml beaker, and a 0.2% aqueous solution of a polymer flocculant containing polyamidine (molecular weight 3 million) and dimethylaminoethyl methacrylate polymer (molecular weight 4 million) in a 50/50 ratio is added. It added so that it might become% vs. SS, and the 1st stirring was performed for 30 second at 800 rpm using the commercially available hand mixer.

  Next, the above polymer flocculant aqueous solution is added to the sludge after the first stirring so as to be 0.7% vs. SS, and stirred at 80 rpm for 1 minute using a jar tester to flocculate flocs (flocculation Product). After measuring the size of the aggregated floc, the mixture of the aggregated floc and the separated liquid was gravity dehydrated with a 60 mesh nylon filter cloth.

The sludge after gravity filtration was sandwiched between two filter cloths and squeezed for 1 minute at a pressure of ² kg / cm ² using a piston type dehydrator to obtain a dehydrated cake. Table 1 shows the results of measuring the size of the aggregated flocs before dehydration, the moisture content of the dehydrated cake, and the peelability of the dehydrated cake.

[Examples 2-6, Comparative Examples 1-8]
The above examples except that the type and mass ratio of the polymer flocculant, a part and the remainder of the required addition amount of the polymer flocculant, and the rotational speeds of the first stirring and the second stirring were the conditions shown in Table 1. The liquid sludge was treated under the same conditions as in the above to obtain a dehydrated cake. Table 1 shows the results of measuring the size of the aggregated flocs before dehydration, the moisture content of the dehydrated cake, and the peelability of the dehydrated cake.

[Measuring method]
1. Aggregate floc size (floc diameter)
The size of the floc was measured with calipers.

2. Cake moisture content Sewage test method 2012 edition, first volume, pages 715 to 716, Volume 5, Section 6 Evaporation residue and moisture content (solid content and moisture) were carried out as described in the item.

3. Cake peelability The peeled state of the dehydrated cake on the filter cloth was visually confirmed.

* 1: “Polymer flocculant” indicates the mass ratio of the polymer flocculant and the compound contained in each test category. Here, A is polyamidine (molecular weight 3 million), B is dimethylaminoethyl methacrylate polymer (molecular weight 4 million), C is acrylamide / dimethylaminoethyl acrylate copolymer (molecular weight 5 million), and D is acrylamide / acrylic acid. -Dimethylaminoethyl acrylate copolymer (molecular weight 4 million), respectively.
* 2: “Addition rate% vs. SS” is the amount of polymer flocculant added per SS (g) of liquid sludge provided for the treatment of each test category before the first stirring. The percentage of the solid amount (g) is shown as a percentage.
* 3: “Agitation rotational speed rpm” indicates the rotational speed of the hand mixer during the first agitation.
* 4: “Addition rate% vs. SS” is the solid content of the polymer flocculant added per SS solid amount (g) of the liquid sludge provided for the treatment of each test category after the first stirring. The ratio of the amount (g) is expressed as a percentage.
* 5: “Agitation rotational speed rpm” indicates the rotational speed of the jar tester during the second agitation.
* 6: “Flock diameter mm” indicates the size of the aggregates produced after the second stirring, measured by the measurement method “[Measurement method] 1. Agglomerated floc size (floc diameter)”.
* 7: “Cake moisture content%” indicates the moisture content of the dehydrated cake measured by the measurement method of “[Measurement method] 2. Cake moisture content”.
* 8: “Cake peelability” refers to the peelability of a dehydrated cake measured by the measurement method of “[Measurement method] 3. Cake peelability”. ◎ is very good (= almost peeled), ○ is good (= roughly peeled), Δ is bad (= difficult to peel), and x is very bad (= not peeled at all).

[result]
As shown in the comparison between Comparative Examples 5 to 7 and Examples 1 to 6, as the polymer flocculant, only polyamidine (molecular weight 3 million), dimethylaminoethyl methacrylate polymer (molecular weight 4 million) only, acrylamide / dimethylamino, respectively. Test divisions (Comparative Examples 5 to 7) to which only ethyl acrylate copolymer (molecular weight 5 million) was added were test divisions (Examples 1 to 6) to which a polymer flocculant composed of a combination of two kinds of polymers was added. In comparison with, the moisture content of the dehydrated cake was high, and the peelability of the dehydrated cake was poor.

  Further, even in the test section (Comparative Example 8) in which two types of polymers are added as a polymer flocculant, when the first stirring stirring speed is as small as 80 rpm, the first stirring stirring rotation is performed. The moisture content of the dehydrated cake was increased and the peelability was poor as compared with the test category (Example 6) having a large number of 800 rpm.

  Furthermore, even in the test section in which two kinds of polymers were added as a polymer flocculant, the test section (Comparative Examples 1 and 2) in which stirring was performed only in one stage of high-speed stirring (800 rpm) and stirring was performed at low speed. In the test section (Comparative Example 3) conducted in only one stage, the moisture content of the dehydrated cake was increased and the peelability of the dehydrated cake was deteriorated as compared with the test sections of Examples 1 to 6. .

  Further, even in the test category in which two kinds of polymers are added as a polymer flocculant, the test category in which the mass ratio of the polymer mainly composed of aminoalkyl (meth) acrylate is less than 10% by mass (Comparative Example 4) ) Resulted in an increase in the moisture content of the dewatered cake and a worsening of the peelability of the dehydrated cake as compared with the test sections of Examples 1-6.

  In addition, the mass ratio between the polyamidine and the polymer mainly composed of aminoalkyl (meth) acrylate is in the range of 30:70 to 7:30 even between the test categories in which two types of polymers are added as a polymer flocculant. It was shown that the cake moisture content and the cake peelability were good in the test categories (Examples 3 to 4). In particular, the moisture content of the cake and the peelability of the cake are particularly good in the test sections (Examples 1 and 2) in which the mass ratio of the polyamidine and the polymer mainly composed of aminoalkyl (meth) acrylate is 50%. It was shown that.

2 Polymer flocculant 10, 50 Sludge dewatering device 14 First flocculant addition means 20 First stirring means 17 Second flocculant addition means 28 Second stirring means 36 Dehydration means

Claims (7)

A polymer flocculant added to the sludge for agglomeration of sludge after biological treatment of organic waste,
And polyamidine, the mass ratio of the polymer containing the aminoalkyl (meth) acrylate, 10: 90-90: Ri mixture der ranges from 10,
A polymer flocculant, wherein the sludge after biological treatment of organic waste is a digestive juice after methane fermentation treatment of food waste . The polymer containing aminoalkyl (meth) acrylate is selected from the group consisting of dimethylaminoethyl methacrylate homopolymer, acrylamide / dimethylaminoethyl acrylate copolymer, and acrylamide / acrylic acid / dimethylaminoethyl acrylate copolymer. The polymer flocculant according to claim 1, wherein the polymer flocculant is at least one or more. In a sludge dewatering method, a polymer flocculant is added to sludge after biological treatment of organic waste, agglomerates are obtained by stirring the sludge to which the polymer flocculant is added, and the agglomerates are dehydrated. ,
The sludge after the biological treatment of the organic waste is a digestive liquid after the methane fermentation treatment of the food waste,
The polymer flocculant is the polymer flocculant according to claim 1 or 2,
The addition of the polymer flocculant and the stirring are
Add a part of the necessary amount of polymer flocculant to the sludge after the biological treatment and perform the first stirring,
A sludge dewatering method comprising: adding the remainder of the necessary addition amount after the first stirring, and performing the second stirring at a speed slower than the first stirring.   The sludge dewatering method according to claim 3, wherein a ratio of a part of the necessary addition amount of the polymer flocculant and the remaining part is in a range of 10:90 to 90:10. The first stirring is 200 rpm or more;
The sludge dewatering method according to claim 3 or 4, wherein the second stirring is less than 200 rpm. Between the second stirring and the dehydration process,
6. The method according to claim 3, further comprising a concentration step of concentrating the aggregate, wherein an inorganic flocculant is added during the concentration step or after the concentration step and before the dehydration treatment. Sludge dewatering method. A first flocculant addition means for adding a part of the required amount of the polymer flocculant according to claim 1 or 2 to sludge after biological treatment of organic waste;
A first stirring means capable of stirring at a speed necessary for dispersing a part of the polymer flocculant in the sludge to which the part of the polymer flocculant is added by the first flocculant addition means; ,
A second flocculant addition means for adding the remainder of the required amount of the polymer flocculant to the dispersed sludge in which a part of the polymer flocculant has been dispersed by the stirring;
In order to obtain the sludge agglomerates, the second agitation means capable of agitating the dispersed sludge to which the remainder of the polymer flocculant has been added by the second aggregating agent addition means at a speed slower than that of the first agitation means. When,
Dehydrating means for dehydrating the aggregate obtained by stirring of the second stirring means,
The ratio of a part and the remainder of the required amount of the polymer coagulant, 10: 90 to 90: Ri 1:10 der of
The sludge after the biological treatment of the organic waste is a digestive liquid after the methane fermentation treatment of the food waste .

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