JP2008080185A - Sludge dewatering method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sludge dewatering method which enables the generation of solid drainable flocs from general sludge for dewatering, especially hard-to-dewater sludge, and an increase in the amount of treated sludge for dewatering and reduce a moisture content of dewatered cakes in a dewatering process by a sludge dewatering machine. <P>SOLUTION: When organic sludge is treated by one kind of polymer coagulant selected from a (meta)acryl water-soluble polymer, a diallyl ammonium water-soluble polymer, a vinylamine, and a polyamidine water-soluble polymer, the necessary amount of the polymer coagulant is divided into two parts, and the respective divisions are added and mixed, and then the sludge is dewatered by the dewatering machine. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a method for dewatering sludge. It is possible to generate strong floc without using an inorganic flocculant in combination with a sludge for dehydration, using a mixture of various polymer flocculants, or using various polymers together, and perform a good dewatering treatment. The present invention relates to a method for dewatering sludge. That is, when treating organic sludge with a polymer flocculant made of a specific water-soluble polymer, the required amount is divided into two parts, added and mixed, and then dehydrated with a dehydrator. About.

Conventionally, sludge dehydration methods such as screw presses, rotary presses, and multi-disc type dehydrators, which are increasing this year, require a coagulation floc that is strong and well drained. 1) Cationic polymer A method in which a mixture of a flocculant and an amphoteric polymer flocculant is added to sludge and then dehydrated. 2) A method in which an acrylate cationic polymer flocculant and an amphoteric polymer flocculant are added and then dehydrated, or an inorganic flocculant. However, in any of these methods, satisfactory results are not always obtained when dehydrating sludge that is currently increasing.

In recent years, the volume of sludge has been reduced, and when a dehydrated cake is composted, an organic polymer flocculant is used to avoid adverse effects on vegetation caused by heavy metals in the cake. The method of dehydration using only is increasingly desired.

In addition, the combined use of the cationic polymer flocculant and anionic polymer flocculant (two-component method), which has been often used from the aspect of operation management in sludge dewatering, takes time and effort to adjust the balance of the two components. Requires a large amount of chemical use. Moreover, since the moisture content of the dehydrated cake after dehydration is high, it tends to be avoided.
JP-A-9-57299 JP-A-2-31899

Add a mixture of various cationic polymer flocculants and amphoteric polymer flocculants to sludge, then dehydrate, add acrylate cationic flocculant and amphoteric polymer flocculants, then dehydrate, or various cations The method using a combination of a water-soluble polymer flocculant and an anionic polymer flocculant is accompanied by an increase in the amount of drug used, and has a small effect of reducing the water content of the dehydrated cake. Accordingly, in the present invention, in sludge dewatering, the combined use of inorganic flocculants and various polymer flocculants is suppressed, the amount of chemical addition is suppressed, the amount of sludge treated is increased, and the moisture content of the dewatered cake is reduced and strongly increased. An object of the present invention is to provide a method for dewatering sludge that can improve the quality of dewatered water by generating agglomerated floc.

一般式（１）
Ｒ１は水素又はメチル基、Ｒ２、Ｒ３は炭素数１〜３のアルキルあるいはアルコキシル基、Ｒ４は水素、炭素数１〜３のアルキル基、アルコキシル基あるいはベンジル基であり、同種でも異種でも良い、Ａは酸素またはＮＨ、Ｂは炭素数２〜４のアルキレン基またはアルコキシレン基を表わす、Ｘ１は陰イオンをそれぞれ表わす。

一般式（２）
Ｒ５、Ｒ６は水素又はメチル基、Ｒ７、Ｒ８は炭素数１〜３のアルキル基、アルコキシ基あるいはベンジル基、Ｘ２は陰イオンをそれぞれ表わす

一般式（３）
Ｒ_５は水素又はメチル基、Ｒ_６、Ｒ_７は炭素数１〜３のアルキル基、アルコキシ基あるいはベンジル基、Ｘ_２ ⁻は陰イオンをそれぞれ表わす。 As a result of detailed investigations in order to solve the above problems, the present inventors have reached the invention described below. That is, when treating the organic sludge with the polymer flocculant comprising the water-soluble polymers of the following (a) to (c), the necessary amount is divided into two parts, added and mixed, and then dehydrated with a dehydrator. It has been found that the sludge dewatering method can achieve a good dewatering treatment by suppressing the amount of chemicals added without using an inorganic flocculant and various polymer flocculants.
Water-soluble polymer (a) to (c)
(A) A cationic or amphoteric water-soluble polymer obtained by polymerizing a monomer represented by the following general formula (1) or (2) and a crosslinkable monomer as essential components.
(B) A cationic or amphoteric water-soluble polymer obtained by polymerizing a monomer represented by the following general formula (3) and a crosslinkable monomer as essential components and then hydrolyzing with an acid or alkali.
(C) A cationic or amphoteric water-soluble polymer obtained by polymerizing the monomer represented by the following general formula (3), (meth) acrylonitrile and a crosslinkable monomer as essential components, and then hydrolyzing with an acid. molecule.

General formula (1)
R1 is hydrogen or a methyl group, R2 and R3 are alkyl or alkoxyl groups having 1 to 3 carbon atoms, R4 is hydrogen, an alkyl group having 1 to 3 carbon atoms, an alkoxyl group or a benzyl group, which may be the same or different. Represents oxygen or NH, B represents an alkylene group or alkoxylene group having 2 to 4 carbon atoms, and X1 represents an anion.

General formula (2)
R5 and R6 each represent hydrogen or a methyl group, R7 and R8 each represent an alkyl group having 1 to 3 carbon atoms, an alkoxy group or a benzyl group, and X2 represents an anion.

General formula (3)
R ₅ represents hydrogen or a methyl group, R ₆ and R ₇ each represent an alkyl group having 1 to 3 carbon atoms, an alkoxy group or a benzyl group, and X ₂ ⁻ represents an anion.

Use a polymer flocculant made of a specific water-soluble polymer, divide the required amount into organic sludge, repeat mixing, dehydrate with a dehydrator, and use a combination of inorganic flocculants and various polymers Without the use of a flocculant, the amount of chemicals added can be suppressed and a good dehydration treatment can be achieved. Using this method, it is possible to produce a coherent floc that is strong and well drained, so it is most suitable for dehydration using a screw press, rotary press, or multi-disc dehydrator that requires high floc strength, especially when it is put into the dehydrator. However, even in tests for belt presses and centrifugal dehydrators, a good dewatering effect can be obtained because the floc strength is improved.

As the dehydration effect by the divided addition according to the present invention, when the above-mentioned divided addition is performed with the same amount of addition to the sludge when used alone, the drainage is improved by the formation of a very strong flock. As a result, the sludge treatment amount can be improved, the water content of the dehydrated cake can be reduced, and the quality of the dehydrated water can be improved. In addition, in the case where an effect equivalent to the dehydration effect when added in a lump is produced, the necessary addition amount can be reduced by adding in the above-described division.

When the polymer flocculant used in the present invention is divided and added, the division ratio is 30 to 95% in the first stage and 70 to 5% in the second stage. Preferably, the first stage is 50 to 90% and the second stage is 50 to 10%.

With this additive formulation, it is possible to reinforce the coagulation floc against sludge that is easy to coagulate as well as sludge that is difficult to form strong floc, for example, food surplus single sludge and septic sludge, and to significantly improve the water quality of the dehydrated filtrate Therefore, the dehydration effect by each dehydrator can be improved. In particular, it is possible to form a floc that can be sufficiently applied to a screw press or a rotary press dehydrator that requires a strong floc.

The sludge dewatering method of the present invention is characterized in that the solution of the polymer flocculant is added to the sludge in two steps. The present inventors conducted an experiment in which the number of divisions was divided into two or three times and added to the sludge and stirred, but it was confirmed that the two-time divided addition shows a sufficient dehydration effect.

As a factor that the split addition method of the polymer flocculant of the present invention has a significant improvement effect on the dewaterability of sludge, a smaller amount than the total required amount is added to the first stage, and the polymer is uniformly aggregated in the sludge by stirring. Efficient floc that eliminates waste by adding the remaining necessary amount in the second stage after the sludge particles are made to act by the agent to generate a relatively small floc by neutralizing and crosslinking the charge on the particle surface. It is presumed to bring about an increase effect. In the conventional method of adding polymer flocculants at once, it is difficult to disperse quickly and uniformly on the sludge surface even if the added polymer flocculant is added and stirred, and partly contributes to aggregation Therefore, it is presumed that the total amount added is not used efficiently, and as a result, the dehydration effect is not sufficiently exhibited.

As a place where the polymer flocculant is added, there can be considered a method in which one flocculent mixing tank is newly added in addition to the conventional flocculant addition and stirring flocculent mixing tank. Alternatively, a method of adding the flocculant as the first stage to the suction side of the supply pump of the sludge supply pipe entering the coagulation mixing tank and adding it as the second stage to the coagulation mixing tank or the like can be considered. Alternatively, a method of adding and stirring the flocculant as a first stage to the sludge supply tank and adding it as a second stage to the flocculent mixing tank or the like may be considered. In these cases, it is economical because there is no need to install a new apparatus in the divided addition.

Applicable types of sludge are organic sludge generated from sewage treatment facilities, human waste treatment facilities, livestock facilities, food factories, chemical factories, etc., and include raw sludge, surplus sludge, digested sludge, and mixed sludge. The dehydrator can be dehydrated using a conventional model such as a decanter, a filter press, a belt press or a screw press, but preferably a screw press, a rotary press, a multi-disc dehydrator, or a belt press. It is.

The cationic or amphoteric polymer flocculant used in the present invention is a polymer flocculant comprising the following water-soluble polymers (a) to (d).
(A) A cationic or amphoteric water-soluble polymer obtained by polymerizing a monomer represented by the following general formula (1) or (2) and a crosslinkable monomer as essential components.
(B) A cationic or amphoteric water-soluble polymer obtained by polymerizing a monomer represented by the following general formula (3) and a crosslinkable monomer as essential components and then hydrolyzing with an acid or alkali.
(C) A cationic or amphoteric water-soluble polymer obtained by polymerizing the monomer represented by the following general formula (3), (meth) acrylonitrile and a crosslinkable monomer as essential components, and then hydrolyzing with an acid. molecule.

The cationic or amphoteric water-soluble polymer (a) is a water-soluble polymer obtained by polymerizing a (meth) acrylic cationic monomer or a diallyldialkylammonium salt and a crosslinkable monomer as essential components. . Examples of (meth) acrylic cationic monomers include dialkylaminoalkyl (meth) acrylates such as dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, or monohalogens of these monomers It is a quaternary ammonium salt by a chemical compound. Examples thereof include (meth) acryloyloxyethyltrimethylammonium chloride, (meth) acryloyloxy 2-hydroxypropyltrimethylammonium chloride, (meth) acryloylaminopropyltrimethylammonium chloride, and the like. Examples of diallyldialkylammonium salts include diallyldimethylammonium chloride, diallylmethylbenzylammonium chloride, diallyldiethylammonium chloride and the like. These cationic monomers can be used in combination of two or more. The mol% of the cationic monomer is 5 to 100 mol%, preferably 10 to 100 mol%, and most preferably 20 to 100 mol%.

The crosslinkable monomer used in the present invention includes divinyl compounds such as N, N-methylenebis (meth) acrylamide, polyethylene glycol di (meth) acrylate, divinylbenzene, vinyl methylol compounds such as methylol (meth) acrylamide, acrolein, and the like. Vinyl-based aldehyde compounds, vinyl-based ether compounds such as methyl (meth) acrylamide glycolate methyl ether, or N, N-dimethylacrylamide and N, N-diethylacrylamide which are heat-crosslinkable monomers. It is not limited to these. Moreover, the copolymerization ratio with respect to a monomer is 0.0001 to 0.01% by mass, Preferably it is 0.0003 to 0.003%.

Water-soluble polymers obtained by copolymerizing nonionic monomers can also be used. As an example of the nonionic monomer, acrylamide is most preferably used, but a nonionic monomer other than acrylamide may be copolymerized. Examples thereof include N, N-dimethylacrylamide, vinyl acetate, acrylonitrile, methyl acrylate, 2-hydroxyethyl (meth) acrylate, diacetone acrylamide, N-vinylpyrrolidone, N-vinylformamide, N-vinylacetamide, Examples include acryloylmorpholine. The mol% of the nonionic monomer is 0 to 95 mol%, preferably 0 to 90 mol%, and most preferably 0 to 80 mol%.

An amphoteric water-soluble polymer obtained by copolymerizing an anionic monomer can also be used in the sludge dewatering method of the present invention. Examples of the anionic monomer include vinyl sulfonic acid, vinyl benzene sulfonic acid or 2-acrylamido 2-methylpropane sulfonic acid, methacrylic acid, acrylic acid, itaconic acid, maleic acid, and p-carboxystyrene. The mol% of the anionic monomer in these amphoteric water-soluble polymers is 3 to 60 mol%, preferably 5 to 40 mol%.

The water-soluble polymer (b) is a cationic compound obtained by polymerizing N-vinylcarboxylic acid amide monomer and a crosslinkable monomer as essential components and then hydrolyzing with an acid or alkali. Alternatively, it is an amphoteric water-soluble polymer and has a vinylamine structure. The acid used during the hydrolysis is preferably an inorganic strong acid, such as hydrochloric acid, nitric acid or p-toluenesulfonic acid. The alkali is preferably a caustic alkali such as sodium hydroxide or potassium hydroxide. Examples of the monomer N-vinylcarboxylic acid include N-vinylformamide and N-vinylacetamide. The mol% of the cationic group in the molecule after hydrolysis is 5 to 100 mol%, preferably 10 to 100 mol%, and most preferably 20 to 100 mol%. The nonionic structural unit is an unhydrolyzed carboxylic acid amide group and is 0 to 95 mol%, preferably 0 to 90 mol%, most preferably 0 to 80 mol%. Moreover, if an anionic monomer is copolymerized at the time of superposition | polymerization, it will become an amphoteric water-soluble polymer. As the anionic monomer, those described above can be used. Moreover, the above-mentioned thing can also be used for a crosslinkable monomer.

The water-soluble polymer (c) is a cationic or amphoteric polymer obtained by polymerizing N-vinylcarboxylic acid amide monomer, (meth) acrylonitrile and a crosslinkable monomer as essential components and then hydrolyzing with an acid. It is a water-soluble polymer and has a polyamidine structure in the molecule. Examples of the monomer N-vinylcarboxylic acid include N-vinylformamide and N-vinylacetamide. The acid used is preferably an inorganic strong acid, such as hydrochloric acid, nitric acid or p-toluenesulfonic acid. The most common vinyl nitriles to be copolymerized are acrylonitrile. The mol% of the amidine group in the molecule after hydrolysis is 5 to 100 mol%, preferably 10 to 100 mol%, and most preferably 20 to 100 mol%. The nonionic structural unit is an unhydrolyzed carboxylic acid amide group and an unreacted nitrile group, and is 0 to 95 mol%, preferably 0 to 90 mol%, most preferably 0 to 80 mol%. . Moreover, if an anionic monomer is copolymerized at the time of superposition | polymerization, it will become an amphoteric water-soluble polymer. As the anionic monomer, those described above can be used. Moreover, the above-mentioned thing can also be used for a crosslinkable monomer.

The molecular weight of the cationic or amphoteric polymer flocculant is 3 million to 20 million, preferably 3 million to 15 million, and more preferably 5 million to 15 million. The reason for this is that if it is less than 300, the cohesive force is insufficient, and if it is higher than 20 million, the viscosity increases too much and the dehydrating property decreases.

The cationic or amphoteric polymer flocculant used in the present invention can be applied in any form. For example, a paste-like product by an aqueous solution polymerization method, a latex product by a water-in-oil emulsion polymerization method, a powder product by a water-in-oil dispersion polymerization, or a dispersion liquid product by dispersion polymerization in an aqueous salt solution. Considering the dissolution time, latex products and dispersed liquid products are convenient.

The present invention will be described in more detail with reference to the following examples and comparative examples. However, the present invention is not limited to the following examples unless it exceeds the gist.

ＤＭＱ：アクリロイルオキシエチルトリメチルアンモニウム塩化物構造単位
ＤＭＣ：メタクリロイルオキシエチルトリメチルアンモニウム塩化物構造単位
ＤＤ：ジメチルジアリルアンモニウム塩化物構造単位、ＶＡＭ：ビニルアミン塩酸塩構造単位、ＶＡＺ：アミジン塩酸塩構造単位、ＡＭＰ：アクリルアミド２−メチルプロパンスルホン酸ナトリウム構造単位、ＡＡＭ：アクリルアミド構造単位、ＭＢＡ：メチレンビスアクリルアミド重合時対単量体添加量（質量％）（架橋性単量体） (Composition of polymer flocculant used for dehydration) Table 1 shows the composition of the polymer flocculant used in carrying out the present invention.
(Table 1) Composition of cationic or amphoteric polymer flocculant

DMQ: acryloyloxyethyltrimethylammonium chloride structural unit DMC: methacryloyloxyethyltrimethylammonium chloride structural unit DD: dimethyldiallylammonium chloride structural unit, VAM: vinylamine hydrochloride structural unit, VAZ: amidine hydrochloride structural unit, AMP: Acrylamide 2-methylpropanesulfonic acid sodium structural unit, AAM: acrylamide structural unit, MBA: Methylene bisacrylamide during polymerization, monomer added amount (% by mass) (crosslinkable monomer)

For excess sludge (pH; 6.73, SS; 10000 mg / l, TS; 12500 mg / l) generated from a sewage treatment plant (oxidation ditch method), a coagulation test and a squeeze test were conducted for a screw press dehydrator. . 200 ml of this sludge was taken in a poly beaker, 0.8% / TS of the cationic or amphoteric polymer flocculants C-1 to C-10 shown in Table 1 was added, and the beaker was transferred and stirred 20 times. Thereafter, 0.2% / TS was further added, the beaker was transferred, and stirring was performed 20 times. After observing the size of the produced flocs, the filtration rate was measured with a 40 mesh nylon filter cloth. The filtered agglomerates were dehydrated at a press pressure of 2 kgf / cm @ 2 and the cake diameter was measured. The dehydrated cake was dried with a dryer at 105 DEG C. for 12 hours to determine the cake moisture content.

As a result, it was confirmed that the formation of very strong flocculation flocs and the filtration rate were improved, and the cake diameter after press dehydration, which is an index of the goodness of water drainage regarding the dehydrated cake, was reduced, and a good cake moisture content was obtained. . These results are shown in Table 2.

As a comparative test, 1.0% / TS of the cationic or amphoteric polymer shown in Table 1 was added to the sludge, transferred to a beaker, and stirred for 20 times. These results are shown in Table 3.

(Table 2) Example 1

(Table 3) Comparative Example 1

A coagulation test and a squeezing test were conducted on a belt press dehydrator for human waste surplus sludge (pH; 7.03, SS; 14500 mg / l, TS; 16000 mg / l). After taking 200 ml of sludge in a poly beaker, adding 0.8% / TS of the cationic or amphoteric polymer flocculant C-1 to C-10 shown in Table 1 and carrying out the beaker transfer and stirring 20 times Further, 0.2% / TS was added and the beaker was transferred and stirred for 20 times. After observing the size of the generated agglomerated floc, a cylinder with an inner diameter of 7 cm was set on a belt press filter cloth (T-1179L). Filtration and filtration rate were measured. The filtered agglomerate was squeezed and dehydrated at a press pressure of 1.5 kgf / cm @ 2 and the cake diameter was measured. The dehydrated cake was then dried with a dryer at 105 DEG C. for 12 hours to determine the moisture content of the cake.

As a result, it was confirmed that a very strong coagulated floc was formed and the filtration rate was improved, and a good cake moisture content was obtained. In addition, an improvement in peelability, which is important during belt press dehydration, was observed. These results are shown in Table 4.

As a comparative test, a cationic or amphoteric polymer shown in Table 1 was added to 1.0% / TS of sludge at a time, transferred to a beaker and stirred 20 times, and a dehydration test was performed in the same manner. These results are shown in Table 5.

剥離性目視○＞○-＞△＞×の順に効果の良いことを表す (Table 4) Example 2

Visual peelability ○>○->△> X indicates that the effect is good.

(Table 5) Comparative Example 2

The sewage digestion sludge (pH; 7.3, SS; 18500 mg / l, TS; 20500 mg / l) was subjected to an agglomeration test and a squeeze test for a screw press dewatering machine. 200 ml of this sludge was taken in a poly beaker, and 1.2% / TS of the cationic or amphoteric polymer flocculants C-1 to C-10 shown in Table 1 was added, and the beaker was transferred and stirred 20 times. Thereafter, 0.3% / TS was further added, the beaker was transferred, and stirring was performed 20 times. After observing the size of the produced flocs, the filtration rate was measured with a 40 mesh nylon filter cloth. The filtered agglomerates were dehydrated at a press pressure of 2 kgf / cm @ 2 and the cake diameter was measured. The dehydrated cake was dried with a dryer at 105 DEG C. for 12 hours to determine the cake moisture content.

As a result, it was confirmed that the formation of very strong flocculation flocs and the filtration rate were improved, and the cake diameter after press dehydration, which is an index of the goodness of water drainage on the dehydrated cake, was reduced, and a good cake moisture content was obtained. . These results are shown in Table 6.

As a comparative test, a cationic or amphoteric polymer shown in Table 1 was added to 1.5% / TS at a time with respect to sludge, transferred to a beaker and stirred 20 times, and a dehydration test was performed in the same procedure. These results are shown in Table 7.

Table 6 Example 3

(Table 7) Comparative Example 3

Claims (3)

When treating organic sludge with a polymer flocculant composed of the water-soluble polymers of the following (a) to (d), the required amount is added in two parts, and after mixing, dehydration is performed using a dehydrator Sludge dewatering method.
(A) A cationic or amphoteric water-soluble polymer obtained by polymerizing a monomer represented by the following general formula (1) or (2) and a crosslinkable monomer as essential components.
(B) A cationic or amphoteric water-soluble polymer obtained by polymerizing a monomer represented by the following general formula (3) and a crosslinkable monomer as essential components and then hydrolyzing with an acid or alkali.
(C) A cationic or amphoteric water-soluble polymer obtained by polymerizing the monomer represented by the following general formula (3), (meth) acrylonitrile and a crosslinkable monomer as essential components, and then hydrolyzing with an acid. molecule.

General formula (1)
R1 is hydrogen or a methyl group, R2 and R3 are alkyl or alkoxyl groups having 1 to 3 carbon atoms, R4 is hydrogen, an alkyl group having 1 to 3 carbon atoms, an alkoxyl group or a benzyl group, which may be the same or different. Represents oxygen or NH, B represents an alkylene group or alkoxylene group having 2 to 4 carbon atoms, and X1 represents an anion.

General formula (2)
R5 and R6 each represent hydrogen or a methyl group, R7 and R8 each represent an alkyl group having 1 to 3 carbon atoms, an alkoxy group or a benzyl group, and X2 represents an anion.

General formula (3)
R ₅ represents hydrogen or a methyl group, R ₆ and R ₇ each represent an alkyl group having 1 to 3 carbon atoms, an alkoxy group or a benzyl group, and X ₂ ⁻ represents an anion. The sludge dewatering method according to claim 1, wherein the addition mass ratio of the two divisions is 30 to 95:70 to 5. The sludge dewatering method according to claim 1, wherein the cationic polymer flocculant and the amphoteric polymer flocculant have a molecular weight of 3 million to 20 million.