JP2009183889A - Sludge dehydration method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a digested sewage sludge treatment method which is suitable for dehydration treatment by a centrifugal dehydrator or a screw press dehydrator, enables a further reduction of water content in a dehydrated cake, and enables a reduction of the generation of magnesium ammonium phosphate (MAP) scales. <P>SOLUTION: An inorganic coagulant is added to digested sewage sludge, and then a polymer coagulant composition (A) containing a polyamidine-based coagulant and an aminoalkyl (meth)acrylate-based cationic coagulant and having a cation equivalent of less than 5 meq/g is added thereto to subject the material to be treated to hydration treatment. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for dewatering sewage digested sludge.

Organic sludge generated from organic wastewater such as sewage, human waste treatment plant, and food industry is dehydrated with a screw decanter (centrifugal dehydrator), screw press type dehydrator, belt press, etc. using a polymer flocculant, and then landfilled or It is incinerated. Most of the fuel used for incineration of dewatered sludge (hereinafter referred to as dehydrated cake) is used for evaporation of moisture in the dehydrated cake. Generally, when the moisture in the dehydrated cake is reduced by 1%, the fuel used for incineration can be saved by about 10%.
However, in recent years, the water content of the dehydrated cake tends to be high due to reasons such as advanced water treatment and an increase in sludge organic content. For this reason, the fuel cost in incineration disposal is increasing, and in addition to the fuel cost reduction, reduction of the moisture content in the dehydrated cake is also desired from the viewpoint of CO ₂ gas reduction and prevention of global warming.

By the way, generally, mixed raw sludge (mixed sludge of primary sludge and excess sludge) or primary sludge that has been anaerobically digested by microorganisms is called sewage digested sludge. Such sewage digested sludge is as follows: It has characteristics and it is difficult to reduce the water content compared to other sludges.
1. The suspended fixed matter (SS) has a small particle size and low specific gravity.
2. There is little sand and fiber as the core of the aggregated floc.
3. It contains a large amount of colloidal material having negative charge shown in the sludge colloid value.
4). Contains a large amount of inorganic salts such as phosphates and carbonates.

In particular, in a dehydration process using a centrifugal dehydrator or a screw press type dehydrator, it is preferable that the aggregated floc is large and the strength is high, but it is difficult to form such an aggregated floc in the treatment of sewage digested sludge.
For this reason, when dewatering the sewage digested sludge, the water content is high in the method using a centrifugal dehydrator, and the shape of the obtained dewatered cake becomes a highly sticky lump, making it difficult to carry and incinerate. Also, in the method using a screw press type dehydrator, the formed flock is broken in the pressing zone and SS is leaked from the punching plate, resulting in poor separation and high moisture content in many cases.

Regarding the sludge dewatering treatment, as a method of reducing the moisture content of the dewatered cake, (1) a method of adding an inorganic flocculant to organic sludge and then performing a dewatering treatment using an amphoteric polymer flocculant (Patent Document 1), (2) After adding an inorganic flocculant to sewage digested sludge, a method of dehydrating using an acrylate cationic polymer flocculant (Patent Document 2), (3) After adding polyiron sulfate to the sludge, containing polyamidine In addition, a method of adding and mixing a cationic polymer flocculant having a cation equivalent value of 5 or more and dehydrating with a Pelto press type dehydrator (Patent Document 3) is disclosed.
JP 63-158200 A JP-A-7-214100 JP-A-8-173999

The method (1) is effective for general organic sludge, and can significantly reduce the water content. However, for sewage digested sludge, the alkalinity of the sludge is so high that it is necessary to add a large amount of an inorganic flocculant. For this reason, compared with the case where a cationic type flocculant is used independently, a chemical | medical cost will result in 2 times or more, and it is not practical.
Compared with the method (1), the method (2) enables a good dehydration treatment with a relatively small amount of inorganic flocculant added and is put to practical use as an effective means. However, the water content is further reduced. Is required.
The method (3) is not necessarily optimal for various dehydrators.
Further, in the dewatering treatment of sewage digested sludge, magnesium ammonium phosphate (MAP) scale is generated in the dewatered separation liquid piping, etc., and troubles that block the piping are likely to occur. Therefore, it is required to reduce the generation of such MAP scale. The

  The present invention has been made in view of the above circumstances, and in the method for dewatering sewage digested sludge, it is also suitable for dewatering by a centrifugal dewatering machine or a screw press type dewatering machine, and the water content in the dewatered cake can be further reduced. At the same time, it is an object to reduce the generation of the MAP scale.

As a result of examining the properties and dewatering performance of sewage digested sludge in detail, the present inventors have found that the sewage digested sludge contains a large amount of inorganic substances such as alkali phosphates and organic substances such as polysaccharides and proteins. It was found that the substance has a great influence on the dewaterability of sludge.
Then, by adding an inorganic flocculant to the sewage digested sludge, metal ions such as Al and Fe contained in the inorganic flocculant react with phosphate ions, polysaccharides, proteins, etc. in the sludge, It has been found that it can be insolubilized, and as a result, generation of MAP scale can be prevented and dehydration can be improved.
In addition, sewage digested sludge simply condensed with an inorganic flocculant is very fine and difficult to dehydrate as it is, but if a polymer flocculant is used, larger flocs can be formed. is there. As a result of further studies, the present inventors have used a polyamidine-based flocculant and an aminoalkyl (meth) acrylate-based cationic flocculant as a polymer flocculant to form a coarser flocculant floc. The inventors have found that the water content is further reduced, the aggregated floc formed at this time is coarse and strong, and that sewage digested sludge can be dehydrated using a centrifugal dehydrator or a screw press type dehydrator. It was.

That is, the sludge dewatering method of the present invention comprises adding a polyamidine flocculant and an aminoalkyl (meth) acrylate cationic flocculant after adding an inorganic flocculant to sewage digested sludge, and a cation equivalent value of 5 meq / The to-be-processed object which added the flocculant composition (A) which is less than g is dehydrated, It is characterized by the above-mentioned.
The dehydration treatment is preferably performed using a centrifugal dehydrator or a screw press dehydrator.

  According to the sludge dewatering method of the present invention, the sewage digested sludge can be dewatered with high efficiency, and the water content in the dewatered cake can be further reduced. Further, a dehydration process using a centrifugal dehydrator or a screw press dehydrator can be applied.

<Sewage digestion sludge>
The sewage digestion sludge in the present invention means mixed sludge (mixed sludge of primary sludge and excess sludge) or sludge obtained by subjecting primary sediment sludge to an anaerobic digestion treatment.

<Inorganic flocculant>
As the inorganic flocculant used in the present invention, known inorganic flocculants such as sulfate band (aluminum sulfate), ferric chloride, ferrous sulfate, polyiron sulfate and the like can be used. These can be obtained from commercial products. An inorganic flocculant may be used individually by 1 type, and may use 2 or more types together.

<Aggregating agent composition (A)>
The flocculant composition (A) in the present invention contains a polyamidine flocculant and an aminoalkyl (meth) acrylate cationic flocculant.
[Polyamidine flocculant]
The polyamidine flocculant used in the present invention comprises a polymer (P) having a repeating unit (I) represented by the following chemical formula (I). The polymer (P) may have a repeating unit other than the repeating unit (I). The content ratio of the repeating unit (I) in the polymer (P) is 50 mol% or more, preferably 80 mol% or more, and may be 100 mol%.

The polymer (P) having the repeating unit (I) can be produced by a known production method, for example, a method described in Japanese Patent No. 2624089.
The polymer (P) is obtained by copolymerizing N-vinylformamide and acrylonitrile, hydrolyzing the resulting copolymer under hydrochloric acid acidity, and then performing a heat treatment, so that the primary amino group and the cyano group on the inner chain of the molecule are converted. Polymers that are cyclized to form amidine rings are preferred.

The molecular weight of the polymer (P) is preferably 100,000 to 5,000,000, more preferably 1,000,000 to 5,000,000. Below 100,000, the cohesive strength decreases and it is currently difficult to produce a polymer with a molecular weight exceeding 5 million on a commercial basis.
The cation equivalent value Cv (unit: meq / g) of the polymer (P) is preferably 4.0 to 8.0, and more preferably 5.0 to 7.0. If it is smaller than the lower limit of the above range, although the floc is large, the moisture content is inferior, and if it is larger than the upper limit, the floc is small, weakens and dewaters.
The intrinsic viscosity [η] indicating the molecular weight of the polymer (P) is preferably 4 dl / g or more, and more preferably 5 dl / g or more. The higher [η], the easier it is to form larger and stronger flocs, and the better the dehydration process. If [η] is less than 4 dl / g, the flocs are small and tend to be weak, and the dewaterability in centrifugal dewatering and screw press dewatering is deteriorated.
The upper limit of the intrinsic viscosity [η] of the polymer (P) is not particularly limited, but is preferably 12 dl / g or less and more preferably 10 dl / g or less from the viewpoint of productivity.
The method for measuring the cation equivalent value Cv and the intrinsic viscosity [η] of the polymer will be described later. One polyamidine flocculant may be used alone, or a plurality of polyamidine flocculants may be used in combination.

[Aminoalkyl (meth) acrylate cationic flocculant]
The aminoalkyl (meth) acrylate cationic flocculant used in the present invention is a homopolymer of an aminoalkyl (meth) acrylate cationic monomer, or an aminoalkyl (meth) acrylate cationic monomer and a nonionic monomer. (Hereinafter, these may be collectively referred to as a polymer (K)).
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. Tertiary salts such as hydrochlorides and sulfates of
Quaternary salts such as halogenated alkyl adducts such as methyl chloride adducts of the dialkylaminoalkyl (meth) acrylate and aryl halide adducts such as benzyl chloride;
Tertiary salts such as hydrochlorides and sulfates such as dialkyl (meth) acrylamides such as N, N-dimethyl (meth) acrylamide;
And quaternary salts such as halogenated alkyl adducts such as methyl chloride adducts of dialkyl (meth) acrylamide and aryl halide adducts such as benzyl chloride adducts.
Of these, dimethylaminoethyl (meth) acrylate / methyl chloride quaternary salt represented by the following chemical formula (II) is preferable.

（式中、Ｒ^１、Ｒ^２、Ｒ^３はそれぞれＣＨ_３を表わし、Ｘ^１はＣｌを表わす。）

(In the formula, R ¹ , R ² and R ³ each represent CH ₃ and X ¹ represents Cl.)

Examples of nonionic monomers include (meth) acrylamide, styrene, acrylonitrile, vinyl acetate, alkyl acrylate, and the like. Among these, acrylamide represented by the following chemical formula (III) is preferable.
Any of these monomers can be used alone or in combination of two or more.

The polymerization method of the polymer (K) is not particularly limited, and examples thereof include precipitation polymerization, bulk polymerization, dispersion polymerization, and aqueous solution polymerization.
A solid acid may be used together with the polymer (K) 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.

The cation equivalent value Cv of the polymer (K) is not particularly limited, and the flocculant composition (A) is adjusted by adjusting the mixing ratio with the polyamidine flocculant (polymer (P)) according to the sludge properties. Can be adjusted to a preferred range.
The intrinsic viscosity [η] of the polymer (K) is appropriately 5 dl / g or more, and the higher [η], the larger and stronger the floc becomes and the better dehydration treatment becomes possible. If [η] is less than 5 dl / g, the flocs are small and weak, and the dewaterability in centrifugal dewatering and screw press dewatering is deteriorated. The upper limit of the intrinsic viscosity [η] of the polymer (K) is not particularly limited, but is preferably 25 dl / g or less and more preferably 20 dl / g or less from the viewpoint of productivity.
The aminoalkyl (meth) acrylate cationic flocculant may be used alone or in combination of two or more.

[Combination ratio]
The flocculant composition (A) in the present invention is used for dehydration as an aqueous solution diluted in water. The concentration of the aqueous solution is preferably 0.05 to 1.5% by mass, and more preferably 0.2 to 0.5% by mass.
The blending ratio of the polyamidine flocculant and the aminoalkyl (meth) acrylate cationic flocculant in the flocculant composition (A) is such that the cation equivalent value Cv of the flocculant composition (A) after mixing these is 5 meq / There is no particular limitation as long as it is less than g. The mass ratio of the blending amount of the polyamidine flocculant / the blending amount of the aminoalkyl (meth) acrylate cationic flocculant is preferably 80/20 to 20/80, and more preferably 70/30 to 30/70.
When the cation equivalent value Cv of the flocculant composition (A) is 5 meq / g or more, the floc formed by adding the flocculant composition (A) after adding the inorganic flocculant tends to be small and weak, and centrifugal Dewaterability in a dehydrator and a screw press type dehydrator tends to deteriorate.

[Method for Measuring Cation Equivalent Value Cv]
The cation equivalent value Cv (unit: meq / g) in the present invention is a value determined by the colloid titration method shown below.
(1) Take 90 ml of deionized water in a conical beaker, add 10 ml of a 500 ppm sample solution prepared by the method of (2) below, bring the pH to 3.0 with an aqueous hydrochloric acid solution, and stir for about 1 minute. Next, a few drops of toluidine blue indicator are added and titrated with N / 400-polyvinyl potassium sulfate reagent (N / 400-PVSK). The titration rate is 2 ml / min, and the end point is the time when the sample water changes from blue to magenta for 10 seconds or longer. From the titration amount of N / 400-polyvinyl potassium sulfate reagent, the cation equivalent value (Cv) is obtained by the following formula (1).
(2) The sample 500 ppm solution is prepared by the following method. That is, 0.2 g (not converted to a dry product) of the sample is precisely weighed and dissolved with 100 ml of deionized water using a triangular corben with a stopper. The 25 ml is made up with deionized water in a 100 ml volumetric flask.

[Measurement method of intrinsic viscosity [η]]
The intrinsic viscosity [η] in the present invention is a value determined by the following method.
(1) First, the viscosity of the solvent blank is measured.
That is, an Ubbelohde viscometer is set in a thermostat adjusted to 30 ± 0.05 ° C., a 1N-sodium nitrate solution is placed in the viscometer, and after standing for 10 to 30 minutes, the solution is raised. The flow time required for passing between the upper and lower marked lines displayed on the viscometer when it is allowed to flow naturally is measured three times or more, and the average value is taken as the viscosity (t0) of the solvent blank.
(2) Next, the reduced viscosity is calculated by the following method.
The same operation as described above was performed using each 1N-sodium nitrate solution having a sample concentration of 0.10 to 0.02% by mass to pass between the upper and lower marked lines displayed on the viscometer of each solution. The average flow time required is measured, and the average value thereof is taken as the viscosity (t) of each sample solution. Next, the ratio t / t0 for each sample was determined to obtain the relative viscosity η _r, and the specific viscosity η _sp = η _r −1 was determined from these, and these were divided by the respective sample concentrations to obtain the respective samples. The reduced viscosity η _sp / C is calculated.
(3) Next, the intrinsic viscosity is calculated by the following method.
The concentration (g / d1) of the sample solution and the reduced viscosity are plotted, and the intrinsic viscosity [η] is obtained by extrapolation.

<Dehydration method>
First, an inorganic flocculant is added to and mixed with sewage digested sludge, and then the flocculant composition (A) is added. The time from the addition of the inorganic flocculant to the addition of the flocculant composition (A) is not particularly limited.
The object to be treated to which the inorganic flocculant and the flocculant composition (A) are added is dehydrated by a known method. The dehydration treatment can be performed using a known dehydrator such as a screw decanter (centrifugal dehydrator), a screw press type dehydrator or a belt press.
In the present invention, it is possible to perform the dehydration process well even by a centrifugal dehydrator or a screw press type dehydrator, which has conventionally been difficult to dehydrate the sewage digested sludge.
The time from the addition of the flocculant composition (A) to the dehydration treatment is not particularly limited.

According to the present invention, phosphate ions, polysaccharides, proteins and the like in sludge can be insolubilized by adding an inorganic flocculant to sewage digested sludge. Thereafter, by adding a flocculant composition (A) containing a polyamidine flocculant and an aminoalkyl (meth) acrylate cationic flocculant, the dehydration treatment using a centrifugal dehydrator or a screw press dehydrator is improved. Coarse and strong flocs can be formed to the extent possible.
Therefore, the sewage digested sludge can be dehydrated with high efficiency, and the water content in the dehydrated cake can be further reduced. Thereby, reduction of sludge treatment cost is realizable. Moreover, a dehydration process can be performed suitably using a centrifugal dehydrator or a screw press type dehydrator.
In addition, since the phosphorus concentration in the dehydrated separation liquid can be reduced, the production of MAP scale can be suppressed thereby.

  Here, the polyamidine flocculant has a relatively low molecular weight compared to the acrylate flocculant, but has a strong adsorptivity to sludge, and has a small amount of addition compared to the inorganic flocculant to hydrophilic polysaccharides, proteins, etc. Can be hydrophobized. However, according to the knowledge of the present inventors, the polyamidine-based flocculant has a low molecular weight, so it is often difficult to form a large and strong floc alone, especially when an inorganic flocculant is used in combination. However, when an aminoalkyl (meth) acrylate cationic flocculant is used together in a blending amount with a cation equivalent value within a predetermined range, a large and strong floc suitable for centrifugal dehydrators and screw press dehydrators is formed. it can.

Hereinafter, the present invention will be described in more detail using examples, but the present invention is not limited to these examples.
The flocculant composition (A) used in the following Examples and Comparative Examples is prepared by blending the polymers shown in Table 1 as shown in Table 2 to form a 0.3 mass% aqueous solution.

Table 1 shows the monomers used in the synthesis of each polymer and their ratios. Abbreviations of monomers shown in this table are as follows.
PVAD: polyvinylamidine. Intrinsic viscosity [η]: 5.0 dl / g.
DMC: dimethylaminoethyl methacrylate / methyl chloride quaternary salt.
DME: dimethylaminoethyl acrylate / methyl chloride quaternary salt.
AAm: acrylamide.

[Examples 1 to 9]
Using the inorganic flocculant and the flocculant composition (A) shown in Table 3, a dewatering test of sewage digested sludge was performed according to the following procedure.
In the following, each characteristic was measured by the following method.
-SS concentration: Measured based on a standard method (edited by the Japan Sewerage Association, “Sewage Test Method, Vol. 1997,” published on August 25, 1997, p. 116).
・ VTS (loss on ignition) value: Measured based on a regular method (edited by Japan Sewerage Association, “Sewerage Test Method Vol. 1997 edition” p297).
Aggregated floc average particle diameter: measured by visual observation.
Colloid charge amount: Measured based on a conventional method (edited by Tokyo Sewerage Service Co., Ltd., Polymer Flocculant Guide p47-49).
-M alkalinity: Measured based on a standard method (edited by Japan Sewerage Association, “Sewerage Test Method, Vol. 1997, p300”).
-Water content of dehydrated cake: Measured based on a standard method (edited by Japan Sewerage Association, “Sewerage Test Method, Vol. 1997, p. 296-297)”.

As sewage digestion sludge, SS concentration: 2.35 mass%, pH: 7.5, VTS: 65.2 mass%, colloid charge amount: -1.2 meq / l, M alkalinity: 5,600 mg / l Sludge was used.
The stirring device shown in FIG. 1 was used. This stirrer has a variable stirrer 11 and a telescopic stand 12. The variable stirrer 11 includes, for example, a stirring shaft 11a having a diameter of 7.5 to 7.9Φ, a width W of 60 mm, and a thickness T of 2 mm. The stirring blade 11b is provided.

(1) First, 300 ml of the sludge was collected in a 500 ml beaker and set in the stirring device of FIG.
(2) An inorganic flocculant shown in Table 3 was added so as to have an addition amount shown in Table 3 (hereinafter the same), and stirred and mixed for 10 seconds at a rotation speed of 900 rpm.
(3) Next, the flocculant composition (A) shown in Table 3 was added so as to have the addition amount shown in Table 3 (hereinafter the same), and the mixture was stirred and mixed at a rotation speed of 900 rpm for 20 seconds.
(4) Next, the agglomerated sludge was filtered through a Nutsche lined with a filter cloth, and the filtrate amount for the first 10 seconds was measured. The results are shown in the column of “10 second filtrate amount” in Table 3.
(5) Subsequently, after 1 minute had elapsed, the concentrated sludge on the filter cloth was sandwiched between filter cloths and squeezed and dehydrated at a pressure of 0.1 MPa for 1 minute to determine the moisture content of the dehydrated cake. The results are shown in Table 3.

[Comparative Examples 1 and 2]
Instead of the flocculant composition (A) in Example 1, a flocculant composition containing a polyamidine flocculant and an aminoalkyl (meth) acrylate cationic flocculant and having a Cv value of 5 meq / g or more was used. Was carried out in the same manner as in Example 1. Table 3 shows the addition amount and each measurement result.

[Comparative Examples 3 and 4]
The flocculant composition (A) in Example 1 was changed to an aminoalkyl (meth) acrylate cationic flocculant in Comparative Example 3, and changed to polyvinylamidine in Comparative Example 4. Others were the same as in Example 1. Table 3 shows the addition amount and each measurement result.

[Comparative Examples 5 and 6]
In Comparative Example 5, the same procedure as in Example 1 was performed except that the inorganic flocculant was not added.
In Comparative Example 5, almost no flocculent flocs were formed and dehydration was impossible. Therefore, in Comparative Example 6, an inorganic flocculant was not added, and the amount of flocculant composition (A) added was set to 1. The amount was 5 times. Others were the same as in Example 1. Table 3 shows the addition amount and each measurement result.

In each of Examples 1 to 9, the particle size of the formed floc was large, and the filtration rate (the amount of filtrate for 10 seconds) and the water content of the dehydrated cake were very excellent.
In Comparative Examples 1 and 2, the floc particle size was small, the filtration rate was slower than those in Examples 1 to 9, and the moisture content was about 4% inferior to Examples 1 to 9.
Comparative Example 3 using only an aminoalkyl (meth) acrylate cationic flocculant as a polymer flocculant and Comparative Example 4 using only a polyamidine flocculant have a smaller floc particle size than the examples, and filtration. The speed was slower than in Examples 1 to 9, and the water content was inferior by about 4% compared to Examples 1 to 9.
In Comparative Example 6 where the inorganic flocculant was not added and the amount of flocculant composition (A) added was increased, flocs were formed, but the filtration rate was slower than in Examples 1 to 9, and the water content was lower. It was greatly inferior compared with Examples 1-9.

Example 10
The inorganic flocculant and the flocculant composition (A) shown in Table 4 were used in the addition amounts shown in Table 4, and a dewatering test of sewage digested sludge was performed according to the following procedure. In this example, the spin-drying | dehydration process was performed using the centrifugal dehydrator (made by Nishihara environmental technology company).
As the sewage digestion sludge, sludge having an SS concentration of 2.1 mass%, a pH of 7.3, a colloid charge amount of −1.7 meq / l, and an M alkalinity of 3,960 mg / l was used.
The inorganic flocculant was added at the outlet of the sludge supply pump of the centrifugal dehydrator. The flocculant composition (A) was added in a centrifugal dehydrator.
The water content of the obtained dehydrated cake was determined. The results are shown in Table 4.
The dehydrated separation liquid was collected and the total phosphorus content (separation liquid TP concentration) was measured. The measurement method is described in “Sewage test method, first volume”, p. 199, “3. Decomposition method with total phosphorus (1) potassium peroxodisulfate”. The results are shown in Table 4. Further, the state of the separation liquid was visually observed, and the case where there was almost no SS and the color of the liquid was white was evaluated as good, and the case where there was a lot of SS and the color of the liquid was black was evaluated as defective. The results are shown in Table 4.

[Comparative Example 7]
The same procedure as in Example 10 was performed except that the flocculant composition (A) in Example 10 was changed to an aminoalkyl (meth) acrylate cationic flocculant. Table 4 shows the addition amount and each measurement result.

[Comparative Examples 8 and 9]
Comparative Example 8 was carried out in the same manner as Example 10 except that no inorganic flocculant was added.
In Comparative Example 8, almost no flocculent flocs were formed and dehydration was impossible. Therefore, in Comparative Example 9, no inorganic flocculant was added, and the amount of flocculant composition (A) added was 1. The amount was 5 times. Others were performed in the same manner as in Example 10. Table 4 shows the addition amount and each measurement result.

In Example 10, the state of the dehydrated separation liquid was also good, the total phosphorus content (TP concentration) in the separation liquid was 7.2 mg / l, and 85% by mass of phosphorus was removed. The moisture content of the dehydrated cake was as low as 71.8%, and the shape was small and good.
In Comparative Example 7, the state of the dehydrated separation liquid was good, but the water content of the dehydrated cake was 77.0%, which was inferior to that of Example 10 by about 5%.
In Comparative Example 9, the total phosphorus content (TP concentration) in the separated liquid was as high as 48.1 mg / l, and the water content was 81.8%, which was a very inferior result compared to Example 10.

It is the schematic which shows the stirring apparatus used in the Example.

Explanation of symbols

11 Variable stirrer, 11a Stirrer shaft, 11b Stirrer blade, 12 Telescopic stand.

Claims (2)

  After adding an inorganic flocculant to sewage digested sludge, a flocculant composition (A) containing a polyamidine flocculant and an aminoalkyl (meth) acrylate cationic flocculant and having a cation equivalent value of less than 5 meq / g A method for dewatering sludge, comprising: dewatering a material to which the material is added.   2. The sludge dewatering method according to claim 1, wherein the dewatering process is performed using a centrifugal dehydrator or a screw press type dehydrator.

Images