JP2001071000A - Dehydration method for pulp or sludge from papermaking industry - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently dehydrate pulp or sludge of the papermaking industry. SOLUTION: An inorg. flocculant is added to pulp or sludge of waste water of the papermaking industry to pref. regulate the pH thereof to 5-8 and an amphoteric polymeric flocculant wherein the sum total of (A) a cation monomer unit and (B) an anion monomer unit is 13-60 mol% and (C) other monomer unit is 40-87 mol% and a molar ratio of (A) the cation monomer unit and (B) the anion monomer unit is 0.03<(B)/(A)<0.8 is added to this pulp or sludge to perform dehydration treatment. As the other monomer unit (C), an acrylamide monomer unit is pref.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for dewatering pulp or papermaking sludge using an inorganic flocculant and an amphoteric polymer flocculant. According to the dehydration method of the present invention, a floc excellent in balance between strength, filtration speed and moisture content can be obtained.

[0002]

2. Description of the Related Art In the pulp industry, a screening process, a cooking process, a bleaching process, a paper making process, and the like.
The wastewater produced is enormous because of the large number of processes that require the use of water. The wastewater generated in these steps is subjected to a physical treatment, and then organic substances are removed by a biochemical treatment such as an activated sludge method. Excess sludge generated at this time is dehydrated by adding a polymer flocculant.

However, the excess sludge generated by the biochemical treatment is very difficult to dehydrate because the main components are cells of living organisms. That is, a dewatered cake is obtained by adding 1% by weight or more of a polymer flocculant per SS, but the water content of the cake is 85% by weight or more and the cake is dehydrated as compared with other industrial wastewater. Has a high moisture content. In some cases, aggregate flocs may not be formed unless 3% by weight or more of a polymer flocculant per SS is added.

Further, the obtained floc is often very brittle, and when the floc is dewatered by using a screw press dewatering machine, the floc often flows out of the screen and the belt press dewatering machine is used. In the case of dehydration, peeling of the dehydrated cake was sometimes difficult.

[0005] As a dehydration method for solving these problems, a method of adding and mixing iron polysulfate and then adding a polymer flocculant, which is known as a usual method of dewatering sludge, is a method of condensing polyamine. It is conceivable to divert a method of adding a polymer flocculant after addition and mixing, and a method of adding an amphoteric polymer flocculant after adding and mixing an inorganic flocculant.

[0006] However, none of the dewatering methods is satisfactory, and the obtained floc does not have strength enough to withstand mechanical dehydration, has an insufficient particle size, and has an insufficient filtration rate. As a result, the throughput per unit time could not be increased, and the resulting cake water content could not be reduced.

[0007]

SUMMARY OF THE INVENTION The present inventors have made various studies to solve the above-mentioned problems, and while adding various inorganic coagulants to pulp or paper industry wastewater sludge, and then performing a dehydration treatment, Using an amphoteric polymer flocculant containing a cationic monomer and an anionic monomer in a specific ratio, it was found that a floc excellent in balance of strength, filtration speed, and water content can be obtained. The invention has been completed. Accordingly, it is an object of the present invention to provide a method for dewatering pulp or papermaking sludge which solves the above problems.

[0008]

The present invention to achieve the above object is as described below. [1] After adding an inorganic flocculant to sludge of pulp or paper industry wastewater, the total of (A) the cationic monomer unit and (B) the anionic monomer unit is 13 to 60 mol%, (C) other And the molar ratio of the (A) cationic monomer unit to the (B) anionic monomer unit is 0.03 <(B) / (A) < A method for dewatering pulp or papermaking industrial sludge, comprising adding an amphoteric polymer coagulant of 0.8 and performing dehydration treatment. [2] The method for dewatering pulp or papermaking industrial sludge according to [1], wherein (C) the other monomer units are acrylamide monomer units. [3] The method for dewatering pulp or paper industry sludge according to [1] or [2], wherein the pH is adjusted to 5 to 8 after adding the inorganic flocculant.

Hereinafter, the present invention will be described in detail.

In the present specification, acrylic acid or methacrylic acid is represented as (meth) acrylic acid, acrylate or methacrylate is represented as (meth) acrylate, and acrylamide or methacrylamide is represented as (meth) acrylamide.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The object of the dehydration method of the present invention is
It is sludge generated when treating pulp or papermaking wastewater discharged from a pulp mill or a paper mill. Specific examples of the sludge include a coagulation sludge obtained by coagulation treatment in which an inorganic coagulant is added to pulp or paper industry wastewater, and an organic polymer coagulant is further added as necessary. Examples include excess sludge obtained by treating activated wastewater with activated sludge, and mixed sludge of coagulated sludge and excess sludge. The present invention is particularly preferably applicable to mixed sludge. Pulp wastewater includes kraft pulp wastewater, sulfite pulp wastewater, bleached wastewater,
Ground pulp wastewater, semi-chemical pulp wastewater, and the like.

The above-mentioned sludge may include various kinds of sludge generated by sludge treatment of domestic wastewater generated in a pulp or paper mill and other wastewater.

In the dewatering method of the present invention, first, an inorganic flocculant is added to the above-mentioned sludge, and the mixture is appropriately stirred as necessary. The stirring conditions themselves are known.

Examples of the inorganic coagulant to be added include commercially available inorganic coagulants known to those skilled in the art, such as a sulfate band, ferric chloride, ferrous sulfate and polyiron sulfate. The amount of these inorganic coagulants varies depending on the properties of the papermaking sludge, but is generally preferably 0.1 to 5% by weight (relative to SS) of the sludge.

After adding the inorganic flocculant to the sludge, its pH is adjusted if necessary. The pH value is preferably 5 to 8. When the pH value is out of the above range, flocculence becomes poor, and the water content of the finally obtained dehydrated cake may increase. The pH is adjusted particularly when the pH after the addition of the inorganic coagulant is in the range of 5 to 8,
It is not necessary to adjust H, and if it is out of this range, it is preferable to adjust the pH by adding an appropriate amount of an alkali or an acid.

In the dewatering method of the present invention, an inorganic coagulant is added, and if necessary, an amphoteric polymer coagulant is added to sludge whose pH has been adjusted, thereby forming flocs. The amphoteric polymer flocculant used in the present invention,
The total of (A) the cationic monomer unit and (B) the anionic monomer unit is 13 to 60 mol%, (C) the other monomer unit is 40 to 87 mol%, and (A) An amphoteric polymer flocculant having a molar ratio of the cationic monomer unit to the (B) anionic monomer unit of 0.33 <(B) / (A) <0.8.

The sum of the components (A) and (B) is 13 mol%
When the amount is less than the above, the sludge having a charge cannot be sufficiently neutralized, and the water content of the obtained cake increases. On the other hand, when it exceeds 60 mol%, the flocculence of the floc decreases, The strength is reduced.

If (B) / (A) is less than 0.03, the particle size of the floc becomes small, or the water content of the cake becomes large. Poor granulation effect, resulting in reduced floc strength.

The amphoteric polymer flocculant used in the present invention can be produced by the following method using the monomers described below.

Cation Monomer The cation monomer which is a constituent material of the amphoteric polymer aggregate is preferably a compound represented by the following formula (1).

[0021]

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(In the formula (1), R ¹ represents a hydrogen atom or a methyl group; A represents an oxygen atom or NH; R ² represents an alkylene having 2 to 8 carbon atoms; R ³ represents a hydrogen atom; . .R ⁴ and R ⁵ represent an alkyl or hydroxyalkyl group having 1 to 8 carbon atoms is an alkyl group having 1 to 8 carbon atoms, it may be the same or different and each (X) ^-
Represents an anion. ) (X) ^- as a halogen atom ion such as chloride ion, and a sulfate ion.

Specific examples of the cationic monomer represented by the above formula (1) include dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate,
Tertiary amine salts such as dialkylaminoalkyl (meth) acrylates such as diethylamino-2-hydroxypropyl (meth) acrylate and dialkylaminoalkyl (meth) acrylamides such as dimethylaminopropyl (meth) acrylamide, such as hydrochlorides and sulfates; Can be illustrated.
Further, quaternary salts such as the above-mentioned dialkylaminoalkyl (meth) acrylate and methyl chloride adduct of dialkylaminoalkyl (meth) acrylamide can also be exemplified.

Hereinafter, more specific examples of cationic monomers that can be used for producing an amphoteric polymer flocculant will be given.

(Meth) acryloyloxyethyldimethylamine hydrochloride, (meth) acryloyloxyethyldiethylamine hydrochloride, (meth) acryloyloxy-2
-Hydroxypropyldimethylamine hydrochloride, or sulfates thereof.

(Meth) acryloyloxyethyltrimethylammonium chloride, (meth) acryloyloxyethyldiethylmethylammonium chloride,
(Meth) acryloyloxy-2-hydroxypropyltrimethylammonium chloride, or methyl sulfate in place of these chlorides.

These cationic monomers may be used alone or in combination of two or more.

Anionic monomer The anionic monomer used in the production of the amphoteric polymer flocculant is preferably (meth) acrylic acid represented by the following formula (2) and salts thereof. As the salts, ammonium salts, alkali metal salts such as sodium and potassium are preferable. These may be used alone or as a mixture of two or more.

[0029]

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(In the formula (2), R ⁶ represents a hydrogen atom or a methyl group; M represents an ammonium ion or an alkali metal ion.) Copolymerizable monomer The above cation monomer and an anion monomer The monomer copolymerizable with the polymer is not particularly limited, and a known nonionic monomer can be used. Specific examples include styrene, acrylonitrile, vinyl acetate, and alkyl (meth) acrylate. These nonionic monomers can be used alone or in combination of two or more.

A particularly preferred copolymerizable monomer is an acrylamide compound represented by the following formula (3).

[0032]

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(In the formula (3), R ⁷ is a hydrogen atom or a methyl group; R ⁸ and R ⁹ are each independently a hydrogen atom;
8 alkyl groups. ) Of these, acrylamide is particularly preferred.

The constituent ratios of the cationic monomer unit, the anionic monomer unit, and the monomer unit copolymerizable with these monomers in the amphoteric polymer flocculant are as described above on a molar basis. Is what you do.

The amphoteric polymer flocculant used in the present invention is obtained by copolymerizing a cationic monomer, an anionic monomer, and a monomer copolymerizable with these monomers in the presence of a known polymerization catalyst. It is manufactured by being made. As the polymerization method, aqueous solution polymerization, reverse phase suspension polymerization, reverse phase emulsion polymerization and the like can be adopted, but usually aqueous solution polymerization is preferable because of easy handling. In the case of aqueous solution polymerization, the total charged concentration of each monomer is:
The content is preferably 25 to 60% by weight.

It is preferable that the pH of the monomer solution is adjusted to 2.5 to 3.5.

The polymerization initiation temperature is usually preferably from 0 to 35 ° C.

[0038] The polymerization time is usually preferably 0.1 to 3 hours. The reaction is preferably performed in an inert atmosphere without oxygen. These polymerization conditions are known.

After the completion of the polymerization reaction, an amphoteric polymer flocculant is obtained by using a known method as needed.

By polymerizing under the above conditions, a high molecular weight amphoteric polymer flocculant having an average molecular weight of several million can be produced. In the dewatering method of the present invention, an inorganic coagulant is added to pulp or papermaking sludge as described above, and p
After adjusting H, the amphoteric polymer flocculant is added, thereby forming sludge floc. The method of forming the flocks conforms to a known method.

The floc thus formed is dewatered 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.

[0043]

The present invention will be described more specifically with reference to the following examples.

(Production Example 1 of amphoteric polymer flocculant) A dimethylaminoethyl methacrylate methyl chloride quaternary salt aqueous solution (hereinafter referred to as DMC), dimethylaminoethyl acrylate methyl chloride 4
Grade salt aqueous solution (hereinafter, referred to as DAC), acrylamide aqueous solution (hereinafter, referred to as AM) and acrylic acid were added, and each was 8.0 mol%, 12.0 mol%, 73.0 mol%,
Distilled water was added so that the composition was 7.0 mol%, the total weight was 1 kg, and the total monomer concentration was 28 wt%. The pH of this solution was adjusted to 2.9. The solution temperature was adjusted to 35 ° C. while blowing nitrogen gas into the solution for 60 minutes, whereby an aqueous monomer mixture solution for polymerization was obtained.

Then, based on the total monomer weight, cupric chloride was used as a copper ion in an amount of 0.3 ppm and azobisamidinopropane hydrochloride (trade name: V-50, manufactured by Wako Pure Chemical Industries, Ltd.) as a polymerization initiator. 60 ppm and sodium bisulfite (NaHSO ₃ ) were added to 30 ppm,
The polymerization was started.

The polymerization was continued for 3 hours while standing. afterwards,
Take out the obtained hydrogel polymer from the Dewar bottle,
Shredded. This was dried at 80 ° C. for 5 hours and then pulverized to obtain a target amphoteric polymer flocculant A.

Using the flocculant A obtained in Production Example 1, the following physical properties were measured. Table 1 shows the results.

Insoluble content: The coagulant was dissolved in pure water,
00 ml of a 0.1% by weight (solid content) solution was prepared. The whole amount of the solution was filtered through a sieve having a diameter of 20 cm and a mesh of 83 mesh, the insoluble matter remaining on the sieve was collected, and the volume was measured.

0.5% salt viscosity: 4% by weight of the above flocculant
Was dissolved in an aqueous sodium chloride solution to prepare a 0.5% by weight flocculant solution. Using a B-type viscometer, 25 ° C, 60
rpm, and the viscosity of the flocculant solution after 5 minutes was measured.

(Production Example 2 of Amphoteric Polymer Flocculant, Comparative Production Example 1 of Amphoteric Polymer Flocculant) The same procedure as in Production Example 1 was carried out except that the amount of the monomer was changed as shown in Table 1. Polymerization was performed to obtain the desired amphoteric polymer flocculants B and C. Also,
Each physical property was measured in the same manner as in Production Example 1.

(Examples 1, 2 and Comparative Example 1) Mixed sludge (pH = 6.8, TS = 36600 mg / L) of coagulated sludge and excess sludge generated by activated sludge treatment of paper mill wastewater
SS = 33400 mg / L, VSS (% of SS) = 6
(1.7%) 200 ml was collected in a 300 ml beaker. After adding 2% by weight of sulfuric acid band (vs. SS), the pH was adjusted to 5.5. In addition, Production Examples 1, 2,
And after adding any of the amphoteric polymer flocculants produced in Comparative Production Example 1, the sludge was removed using a jar tester at 150 rpm.
For 2 minutes to generate sludge flocs.

Subsequently, the sludge was stirred at 560 rpm for 15 seconds using a handy mixer, and the particle size of the generated floc was measured.

Thereafter, the sludge floc dispersion was subjected to gravity filtration using a 60-mesh net as a filter.
The filtration capacity after 10 seconds was measured and indicated as the filtration rate. Using a centrifugal separator, filter the sludge after filtration for 2000 r.
After dehydration at pm for 10 minutes, the water content of the obtained floc was measured. Table 1 shows the measurement results.

[0054]

[Table 1]

[0055]

The amphoteric polymer flocculant used in the present invention has an anion unit, a cation unit, and a nonion unit in the molecule and contains these at a predetermined ratio.
When this is used for dewatering pulp or papermaking sludge, flocculants exhibit extremely efficient coagulation action and are excellent in balance between strength, filtration speed, and moisture content.

Claims (3)

[Claims] After adding an inorganic flocculant to sludge of pulp or paper industry wastewater, (A) a cationic monomer unit and (B)
13-60 mol% in total with anionic monomer units,
(C) The other monomer units are 40 to 87 mol%, and the molar ratio of the (A) cationic monomer unit to (B) anionic monomer unit is 0.03 <(B) / (A) <0.
8. A method for dewatering pulp or papermaking industrial sludge, comprising adding an amphoteric polymer flocculant of No. 8 and performing dehydration treatment. 2. The method for dewatering pulp or paper industry sludge according to claim 1, wherein (C) the other monomer units are acrylamide monomer units. 3. After the addition of the inorganic coagulant, the pH is adjusted to 5-8.
The method for dewatering pulp or papermaking industrial sludge according to claim 1 or 2, wherein the sludge is adjusted to the following conditions.