JP2002177706A - Amphoteric high molecular flocculating agent and method of dehydrating sludge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high molecular flocculating agent having excellent flocculating and dehydrating performance and capable of obtaing low water content cake by adding a little quanty thereof, and to provide a method of dehydrating sludge. SOLUTION: The high molecular flocculating agent is an amphoteric high molecular flocculating agent consisting of >=2 kinds of amphoteric high molecular compounds different in ion equivalent. The sludge is dehydrated by adding the amphoteric high molecular flocculating agent after adding or without adding an inorganic flocculating agent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amphoteric polymer flocculant which is excellent in flocculating and dewatering performance and gives a cake having a low water content, and a method for dewatering sludge using the same.

[0002]

2. Description of the Related Art Conventionally, a cationic polymer flocculant has been used alone for dewatering sludge. However, in recent years, an increase in the amount of sludge generated and deterioration of sludge properties have led to the conventional cationic polymer flocculant. The treatment conditions are not always satisfactory in terms of the sludge treatment amount, the water content of the dewatered cake, the SS recovery rate, and the removability of the cake from the filter cloth. Is required.

[0003] In order to improve these disadvantages of the conventional cationic polymer flocculants, various dehydration methods using amphoteric polymer flocculants have been proposed, but they have not been sufficiently satisfactory. For example, (1) an amphoteric polymer flocculant having a tertiary amino group (JP-A-62-205112),
(2) amphoteric polymer flocculant containing a quaternary ammonium group (JP-A-53-149292); and (3) amphoteric polymer flocculant containing a tertiary-quaternary polymer (JP-A-3-18900). It has been known.

[0004] However, in the dehydration method (1), although the coagulability is superior to that of the conventional cationic polymer coagulant and a large coagulated floc is formed, the pH of sewage and night soil digested sludge is high. For sludge, the performance is significantly reduced due to the problem of the dissociation state of the tertiary amino group, and it is susceptible to sludge property changes such as sludge concentration including pH, and stable treatment cannot be performed. There are drawbacks such as inferior to conventional cationic polymer dehydrating agents in terms of stability of the product in a powder or solution state. Further, in the dehydration method (2), the product stability is better than the amphoteric polymer flocculant containing a tertiary amino group, and the flocculant has a stronger flocculence than the conventional cationic polymer flocculant. However, there are many points to be improved, such as a large required amount of addition, a high water content of the cake, and poor removability of the cake from the filter cloth. On the other hand, (3)
Although the disadvantages of the methods (1) and (2) have been improved, the dehydration method of (1) is not yet at a satisfactory level in terms of the required amount of addition and the cake moisture content, and is not improved in practical use. Is required.

[0005]

SUMMARY OF THE INVENTION The present invention overcomes the drawbacks of the conventional sludge dewatering method and provides a cake having excellent coagulation dewatering performance, requiring a small amount of addition, and having a low water content. In order to find a polymer flocculant and a method of dewatering sludge that could be used, the present inventors conducted intensive studies.

[0006]

The present inventors have conducted various studies to solve the above-mentioned problems, and as a result, a polymer flocculant containing two or more amphoteric polymers having different ion equivalents is effective. Thus, the present invention has been completed. Hereinafter, the present invention will be described in detail. In this specification, acrylate or methacrylate is represented as (meth) acrylate, acrylamide or methacrylamide is represented as (meth) acrylamide, and acrylic acid or methacrylic acid is represented as (meth) acrylic acid.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Amphoteric polymer flocculant The amphoteric polymer constituting the amphoteric polymer flocculant of the present invention is a copolymer having a cationic monomer unit and an anionic monomer unit as essential constituent monomer units. good.

The cationic monomers include dialkylaminoalkyl (meth) acrylate hydrochloride such as dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate and diethylamino-2-hydroxypropyl (meth) acrylate, and sulfuric acid. Tertiary salts such as salts; quaternary salts such as halogenated alkyl adducts such as methyl chloride adduct of dialkylaminoalkyl (meth) acrylate and aryl halide adducts such as benzyl chloride adduct; N, N-dimethyl ( Tertiary salts such as hydrochlorides and sulfates of dialkyl (meth) acrylamides such as meth) acrylamide; aryl halides such as methyl chloride adducts of dialkyl (meth) acrylamide and benzyl chloride adducts Quaternary salts such as adducts; That.

Examples of the anionic monomers include (meth) acrylic acid and alkali metal salts or ammonium salts such as sodium salt; maleic acid and the like; and alkali metal salts thereof; acrylamide such as acrylamide-2-methylpropanesulfonic acid. Alkylalkanesulfonic acid and its alkali metal salt or ammonium salt; and vinylsulfonic acid and its alkali metal salt or ammonium salt and the like.

As the amphoteric polymer, a monomer other than the above-mentioned monomers, specifically, a nonionic monomer may be used in combination, if necessary. As the nonionic monomer,
Dialkylaminoalkyl (meth) acrylates such as (meth) acrylamide and dimethylaminoethyl (meth) acrylate, dialkylaminopropyl (meth)
Dialkylaminoalkyl (meth) such as acrylamide
Examples thereof include acrylamide, styrene, acrylonitrile, vinyl acetate, alkyl acrylate, alkyl methacrylate, vinyl pyridine, vinyl imidanol, and allylamine. Among these, (meth) acrylamide is preferred.

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

Preferred combinations of the monomers in the present invention include a tertiary or quaternary salt of a dialkylaminoalkyl acrylate as a cationic monomer, an acrylate and a nonionic monomer as an anionic monomer. Copolymers of acrylamide, tertiary or quaternary salts of dialkylaminoalkyl methacrylates as cationic monomers, acrylates as anionic monomers and copolymers of acrylamide as nonionic monomers, and Tertiary or quaternary salts of dialkylaminoalkyl methacrylates as cationic monomers, tertiary or quaternary salts of dialkylaminoalkyl acrylates, acrylates as anionic monomers and acrylamide as nonionic monomers There is a copolymer of

The amphoteric polymer flocculant of the present invention comprises two or more amphoteric polymers having different ion equivalents. As the ion equivalent of the amphoteric polymer, the cation equivalent value (hereinafter referred to as Cv) is preferably from 0.5 to 4.8 meq / g, more preferably from 1.0 to 4.8 meq / g,
Anion equivalent value (hereinafter referred to as Av) is 0.2 to 2.5 m
eq / g, more preferably 0.3
-1.8 meq / g. The above Cv and Av are comprehensively determined in consideration of the solubility of the flocculant in water, the flocculation performance for sludge, and the dewatering property of the flocculant. However, in general, Cv and Av are too low. When it is too high, the coagulation performance is reduced. When it is too high, the coagulation performance itself is good, but the dewatering property of the floc tends to deteriorate.

The Cv and Av of the amphoteric polymer in the present invention can be determined by the following colloid titration method.

1) Measurement of Cv (1) Titration method Take 90 ml of deionized water in a conical beaker, add 10 ml of a 500 ppm solution of the sample, adjust the pH to 3.0 with an aqueous hydrochloric acid solution, and adjust the pH to about 1
Stir for a minute. Next, 2-3 tolidine blue indicator was added.
Add dropwise and titrate with N / 400 polyvinyl potassium sulfate reagent (hereinafter referred to as N / 400 PVSK). The titration speed is 2
ml / min, and the point at which the sample changes color from blue to reddish purple for 10 seconds or more is determined as the end point. (2) Preparing a 500 ppm aqueous solution of a sample 0.2 g of a sample (not converted to dry product) is precisely weighed,
Take in a stoppered triangular Kolben and dissolve in 100 ml of deionized water. This 25 ml is made up with deionized water in a 100 ml volumetric flask. (3) Calculation method

[0016]

(Equation 1)

2) Measurement of Av (1) Titration method In a conical beaker, take 90 ml of deionized water, add 10 ml of a 500 ppm solution of the sample, adjust the pH to 7.0 with a sodium hydroxide aqueous solution, and stir for about 1 minute. Next, 2-3 drops of toluidine blue indicator are added, and titration is performed with an N / 400 polyvinyl potassium sulfate reagent (hereinafter, referred to as N / 400 PVSK). The titration rate was 2 ml / min, and the sample changed color from blue to magenta.
The point when the time is held for 0 second or more is defined as the end point. (2) Sample 500
Precisely weigh 0.2 g (not converted to dry product) of a prepared sample of a ppm aqueous solution, place it in a stoppered triangular kolben, and add 100 parts of deionized water.
Dissolve in ml. This 25 ml is made up with deionized water in a 100 ml volumetric flask. (3) Calculation method

[0018]

(Equation 2)

The molecular weight of the amphoteric polymer is 5 to 120 mPa in terms of 0.5% salt viscosity which is an index of the molecular weight.
.S, and more preferably 15 to 90 mPa · s in order to achieve stable dehydration treatment.
The 0.5% salt viscosity was determined by dissolving a 0.5% amphoteric polymer in a 4% aqueous sodium chloride solution at 25 ° C. at 25 ° C. using a B-type viscometer. Measure at 60 rpm using 1 or 2.

The method for producing the amphoteric polymer is not particularly limited, and a general polymerization method can be employed. For example, in the case of aqueous solution polymerization, potassium persulfate, ammonium persulfate, 2,2′-azobis (2-amidinopropane) dihydrochloride, a redox-based initiator, or the like can be used as a polymerization initiator. In the case of reverse-phase emulsion polymerization, the polymerization may be carried out using a water-insoluble initiator such as azobisisobutyronitrile and benzoyl peroxide in addition to the polymerization initiator.

The amphoteric polymer flocculant of the present invention can be produced by mixing two or more amphoteric polymers having different ion equivalents as described above. Further, in the dewatering of sludge, each component can be separately added. In the case where two types of amphoteric polymers are used, the ratio of the amphoteric polymers is 10 to 9 having a specific ion equivalent.
0% by mass and other specific ion equivalent amphoteric polymer 9
The range of 0 to 10% by mass is preferable, and even when three or more amphoteric polymers are used, it is preferable that each component is in these ranges. The ion equivalent of the amphoteric polymer flocculant is preferably in the same range as the preferred ion equivalent of the amphoteric polymer described above. When the amphoteric polymer flocculant is used, it may be used by mixing with known additives such as sodium hydrogen sulfate, sodium sulfate and sulfamic acid as long as the dehydration treatment is not adversely affected.

2. Sludge Dewatering Method The flocculant of the present invention is applicable to various sludges, and organic sludge and flocculated sludge generated in sewage, night soil, and general industrial wastewater such as food industry, chemical industry and pulp or paper industry sludge. And the like.

The dehydration method using a flocculant of the present invention is, specifically, a method of adding a flocculant to sludge and thereby forming a sludge floc. The method for forming the flocs may be a known method.

In the present invention, it is preferable to add the above-mentioned amphoteric polymer flocculant after adding the inorganic flocculant or the organic cationic compound.

As the inorganic coagulant, aluminum sulfate,
Examples thereof include polyaluminum chloride, ferric chloride, ferrous sulfate and polyiron sulfate.

Examples of the organic cationic compound include polymer polyamines, polyamidines, and cationic surfactants.

Further, in the present invention, it is preferable to adjust the pH to 4 to 8 after adding the inorganic flocculant or the organic cationic compound, because the sludge can be more effectively treated. As a method for adjusting the pH, if an inorganic coagulant or an organic cationic compound is added and then the pH value is satisfied, no particular pH adjustment is required. Alternatively, it is adjusted by adding an alkali. Examples of the acid include hydrochloric acid, sulfuric acid, acetic acid, and sulfamic acid. Examples of the alkali include caustic soda, caustic potash, slaked lime, and ammonia.

The amount of addition of the amphoteric polymer flocculant, the inorganic flocculant and the cationic compound, the stirring speed and the stirring time may be in accordance with the conventional dehydration conditions. Further, it can be used in combination with another cationic polymer or anionic polymer, or can be added to a dehydrating agent and used as one mixed liquid.

The floc thus formed is dehydrated using a known means to obtain a dewatered cake.

Examples of the dehydrator include a screw press dehydrator, a belt press dehydrator, a filter press dehydrator and a screw decanter.

The coagulant of the present invention is also applicable to a dehydration method using a granulating and concentrating tank having a filtration unit. Specifically, to the sludge, after adding an inorganic flocculant and further adding a polymer flocculant, or together with the polymer flocculant, introducing the sludge into a granulating and concentrating tank having a filter section, A method of removing the filtrate from the solution, granulating the granulated product, and dehydrating the granulated product with a dehydrator is exemplified.

[0032]

The present invention will be described more specifically with reference to examples and comparative examples. In the following, “parts” means parts by mass. Further, as the amphoteric polymer constituting the flocculant, a mixture of the amphoteric polymer shown in Table 1 below and the amphoteric polymer shown in Table 2 below was used. The abbreviations in Table 1 have the following meanings. DMC: quaternary methyl chloride salt of dimethylaminoethyl methacrylate DAC: quaternary methyl chloride salt of dimethylaminoethyl acrylate
A: Acrylic acid / AMD: Acrylamide

[0033]

[Table 1]

[0034]

[Table 2]

Example 1, Comparative Examples 1 to 3 Sewage sludge (T
S: 8900 mg / l, VTS: 53.9% vs. TS, S
S: 5600 mg / l, VSS: 71.4% vs. SS) 2
00 ml was collected in a 300 ml beaker, and after adding the polymer flocculant shown in Table 3, 200 ml was added using a jar tester.
The mixture was stirred for 1 minute at rpm to generate sludge floc, and the particle size of the floc was measured. Then, the sludge floc dispersion was gravity filtered using an 80 mesh filter cloth as a filter. The filtrate volumes after 5, 10, 20, and 30 seconds were measured. Further, the appearance of the obtained filtrate was evaluated on a five-point scale. The obtained cake was subjected to compression dehydration using a belt press, and the water content was measured. Table 3 shows the measurement results.

[0036]

[Table 3]

Example 2, Comparative Examples 4 to 6 Sewage sludge (T
S: 15700 mg / l, VTS: 80.9% vs. TS, S
S: 13000 mg / l, VSS: 82.3% vs. SS)
200 ml was collected in a 300 ml beaker, and after adding a polymer flocculant shown in Table 4, 10 ml was added using a jar tester.
Stir at 00 rpm for 10 seconds to generate sludge floc,
The particle size of the floc was measured. Then, the sludge floc dispersion was gravity filtered using an 80 mesh filter cloth as a filter. The filtrate volumes after 5, 10, 20, and 30 seconds were measured. Further, the appearance of the obtained filtrate was evaluated on a five-point scale. The obtained cake was subjected to compression dehydration at 2,000 rpm for 10 minutes using a centrifugal sedimentation tube containing an 80 mesh filter cloth therein, and the water content was measured. Table 4 shows the measurement results.

[0038]

[Table 4]

[0039]

According to the amphoteric polymer flocculant and the method for dewatering sludge of the present invention, the effect can be exerted with a small amount of addition, and a coagulation dewatering performance such as a filtration rate is excellent, and a cake having a low water content can be obtained. Can be.

Continued on the front page F term (reference) 4D015 BA08 BA11 BB08 BB09 BB12 BB17 CA03 CA11 CA12 DA04 DA05 DA13 DA15 DA16 DB07 DB13 DB44 DC06 EA13 EA14 EA16 EA17 EA39 4D059 AA01 AA03 AA06 BE10 BE15 BE37 BE55 DA12 BE12 BE17 DA17 DB23 DB26

Claims (3)

[Claims] An amphoteric polymer flocculant comprising two or more amphoteric polymers having different ion equivalents. 2. A method for dewatering sludge, comprising adding the amphoteric polymer flocculant according to claim 1 to sludge and then dewatering the sludge. 3. After adding an inorganic flocculant to the sludge,
A method for dewatering sludge, comprising adding the amphoteric polymer flocculant according to claim 1, followed by dewatering.