JP2668711B2 - Paper and pulp wastewater coagulation treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to a method for coagulating waste water containing paper / pulp components discharged from a paper mill or the like as a suspension.

[Conventional technology]

Aluminum sulfate,
A method of performing an aggregating treatment using an inorganic aggregating agent such as polyaluminum chloride and a nonionic or anionic polymer aggregating agent such as polyacrylamide or a hydrolyzate thereof in combination is generally used. In this case, the pH of the wastewater is usually acidified when an inorganic coagulant is added, so that the pH is adjusted with an alkali if necessary.

[Problems to be solved by the invention]

However, when the inorganic coagulant and the anionic polymer coagulant are used together, good coagulation treatment cannot be performed unless the pH of the wastewater lowered by the inorganic coagulant is adjusted to near neutral. It requires a large amount of alkali and is not economically preferable.

When an inorganic flocculant and a nonionic polymer flocculant are used together, floc is formed and flocculation is performed even in a low pH region, that is, on the acidic side, but the size and strength of the floc are not sufficient and are not always satisfactory. No results have been obtained.

In view of the present situation, the present inventors have examined a treatment method that does not require pH adjustment and has excellent flocculation performance, and consolidate paper / pulp wastewater by co-using a specific inorganic flocculant and a specific organic polymer flocculant. A method was found and the present invention was completed.

[Means for solving the problem]

The gist of the present invention is to add an aluminum salt-based inorganic coagulant to paper / pulp wastewater, and then add acrylamide and the following monomer (a) Is a copolymer having a weight composition ratio of 98 to 50: 2 to 50 and a chaotic polymer flocculant having an intrinsic viscosity [η] of 8 or more.

The paper / pulp wastewater to be treated in the present invention is a wastewater containing paper / pulp components discharged from a paper mill or the like as a suspension.

Aluminum salt-based inorganic coagulants such as aluminum sulfate and polyaluminum chloride are first added to these wastewaters, but suspended particles in paper / pulp wastewater, which usually have a negative charge, are not added by the inorganic coagulant. The negative charge is then neutralized to form a fine floc.

The addition amount of these inorganic coagulants may be appropriately selected according to the properties of the wastewater, but it is usually added to the wastewater in an amount of about 2 to 100 ppm in terms of aluminum.

The pH value of the wastewater is lowered and becomes acidic by the addition of the inorganic coagulant, but in the present invention, the chaotic polymer coagulant is usually added without special pH adjustment. However, pH
When the value is lower than 5.5, the cohesiveness decreases, so that a better result can be obtained by adjusting the pH value in the range of 5.5 to 7.0 by adding a little alkali component.

In the present invention, a specific chaotic organic polymer flocculant is added subsequent to the addition of the inorganic flocculant, whereby the flocculation floc grows into a larger floc and has a strong strength and good sedimentation. Become a flock.

The above-mentioned copolymer is used as the chaotic polymer flocculant, and as the chaotic monomer (a), dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, diethylaminoethyl acrylate, dimethylaminoethyl acrylate, dimethylaminopropyl methacrylamide. , Dimethylaminopropylacrylamide, and the like, and quaternary ammonium salts.

In this chaotic polymer flocculant, if the weight composition ratio of acrylamide to the chaotic monomer (a) is out of the above range, the flocculation performance is deteriorated, which is not preferable. That is, when a flocculant having a content of the chaotic monomer (a) exceeding 50 parts by weight is used, a large floc is formed, but the flocculence is poor due to poor flocculation, and the sedimentation is insufficient and the water flow is reduced. Therefore, there is a problem that the flocks are destroyed and minute flocs flow into the treated water. If the content of the monomer (a) is less than 2% by weight, the negative charge of the suspension will not be sufficiently neutralized and the CO
The D value is high and the clarity is insufficient. Incidentally, the weight composition ratio of both monomers in the chaotic polymer flocculant is 95 to 7
The range of 0: 5 to 30 is more preferable.

In consideration of the floc size, tightness, etc., the chaotic polymer flocculant has an intrinsic viscosity [η] (1N-NaNO ₃ , 30
C) is preferably 8 (dl / g) or more.
(Dl / g) or more is more preferable.

〔Example〕

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

Various measurements were performed according to the following methods.
Further, in the examples, a chaotic polymer flocculant comprising acrylamide and the chaotic monomer (a) shown in Table 1 was used.

(1) Degree of Kaothin Take 90 ml of deionized water in a conical beaker, add 10 ml of a 500 ppm solution of the sample polymer, adjust the pH to 4.0 with an aqueous hydrochloric acid solution, and stir for about 1 minute.

Next, add 2-3 drops of toluidine-indicator and add N / 40
0 Titrated with polyvinyl potassium sulfate (PVSK) reagent.

The titration speed was 2 ml / min, and the sample changed color from blue to magenta.
The end point is the time of holding for 10 seconds or more.

 The degree of chaotin is determined by the following formula.

(2) Degree of anion Take 90 ml of deionized water in a conical beaker, add 0.5 ml of an N / 10 aqueous solution of caustic soda, add 5 ml of N / 20 methyl glycol chitosan reagent dropwise with stirring, and stir for 1 minute or more.

Next, 10 ml of a 500 ppm solution of the sample polymer is slowly added dropwise, and after the addition, the mixture is stirred for 5 minutes or more. Then, 2 to 3 drops of toluidine-indicator are added, and titrated with N / 400 polyvinyl potassium sulfate (PVSK) reagent.

The titration speed was 2 ml / min, and the sample changed color from blue to magenta.
The end point is the time of holding for 10 seconds or more.

In the above operation, the case where no sample is added is defined as a blank test.

 The degree of anion is determined by the following formula.

(3) Coagulation sedimentation test (Jar test) Add 500 ml each of paper mill wastewater adjusted to a predetermined pH by adding an inorganic coagulant to a beaker, place it in a jar tester, add and mix a predetermined amount of a polymer coagulant, Measure sedimentation velocity and COD of treated water.

Examples 1 to 4 and Reference Examples 1 to 4 A When polyaluminum chloride (200 ppm) was added to the papermaking wastewater (COD 215 ppm) of the paper mill, the pH was 5.7.
A 500 ml portion of this solution was taken into a beaker, placed in a beaker, and the polymer flocculant shown in Table 1 was added at a ratio of 0.5 ppm / waste water at a ratio of 0.5 ppm / waste water, followed by stirring and mixing. The floc diameter, floc sedimentation speed, and treated water COD was measured.

The results are shown in Table 2. In all cases, the flock diameter was large, the sedimentation time was short, and the flock strength and tightness were good.

After adding polyaluminum chloride,
A pH value was adjusted to 6.8, and other conditions were the same as in Examples 1 to 4, and an aggregation test was carried out. Good results were obtained also in this case (Reference Examples 1 to 4).

Comparative Examples 1 to 4 Polymer flocculants of Table 1 were used to evaluate the flocculation performance under the same conditions as in Example 1, and the results of Table 2 were obtained. In each case, the floc diameter is small, the sedimentation time is long, and the COD
Value was high, too.

Examples 5 to 8 When 250 ppm of aluminum sulfate was added to the papermaking wastewater (COD 160 ppm) of the B paper mill, the pH value became 6.3. 500 ml each of this solution was placed in a beaker and placed on a jar tester to give 0.8 ppm of each polymer coagulant in Table 1.
/ Add the wastewater at a ratio and stir-mix, measure the floc diameter, flocculation rate, treated water COD, etc., and obtain the results shown in Table 2.

In each case, the floc diameter was large, the sedimentation time was short, and the floc strength and tightness were good.

Comparative Examples 5 to 8 Polymer aggregation agents shown in Table 1 were used to evaluate the aggregation performance under the same conditions as in Example 5, and the results shown in Table 2 were obtained. In each case, the floc diameter was small and the sedimentation time was long.

[Effects of the Invention] According to the method of the present invention, it is possible to form a floc having sufficient size and strength and excellent sedimentation property, and to perform coagulation treatment of paper / pulp wastewater without pH adjustment by addition of alkali. Can be done.

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Claims (1)

(57) [Claims] 1. A copolymer in which an aluminum salt-based inorganic coagulant is added to paper / pulp wastewater, and then a weight composition ratio of acrylamide and the following monomer (a) is 98-50: 2-50. Yes A method of coagulating paper / pulp wastewater, which comprises adding a cationic polymer coagulant having an intrinsic viscosity [η] of 8 or more.