JP3222247B2 - Sludge dewatering method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for dehydrating an organic sludge, and more particularly to a method for economically and advantageously using an alkaline earth metal salt and an organic polymer flocculant having a specific structure in combination. The present invention relates to a method for performing dehydration.

[0002]

2. Description of the Related Art Organic sludge generated from biological treatment facilities such as activated sludge treatment in sewage treatment plants, human waste treatment plants, and various factories is mixed with an appropriate dehydrating agent and then mechanically dewatered by filtration or centrifugation. As such a dehydrating agent for organic sludge, a method of coagulating sludge with an acrylic organic polymer coagulant and then dehydrating with a belt press or a decanter, or adding ferric chloride and calcium hydroxide to the sludge to form a vacuum The method of filtering is common. In addition, a method of adding an organic polymer flocculant to a metal hydroxide-containing sludge to which an aluminum salt such as polyaluminum chloride, a sulfate band, and polyiron sulfate has been added, is also known.

As an organic polymer flocculant effective for such a metal hydroxide-containing sludge, a flocculant having both an anionic group and a cationic group is considered to be effective, and an acrylic anion such as acrylic acid / acrylamide copolymer is used. Acrylic based on acrylic polymer composed of acrylic polymer such as Mannich-modified polyacrylamide and dialkylaminoalkyl (meth) acrylate or dialkylaminoalkyl (meth) acrylamide salt or quaternary compound Mixtures with cationic polymeric flocculants are known.

There have also been proposed various amphoteric polymer flocculants comprising a hydrazine-modified polyacrylic acid or a polymer of a monomer containing the above-mentioned acrylic cationic monomer and an anionic monomer such as acrylic acid. It is also known to mix polymeric flocculants with other acrylic polymeric flocculants.

In contrast to these acrylic organic polymer flocculants which have been widely used in the past, a primary product such as a hydrolyzate of an N-vinylcarboxylic acid amide (co) polymer, a Hofmann decomposition product of polyacrylamide, polyethyleneimine, polyvinylimidazoline, etc. Alternatively, polymers containing secondary amines are known as organic sludge dehydrating agents.

Among them, a hydrolyzate of an N-vinylcarboxylic acid amide (co) polymer has recently attracted attention and has been disclosed in
-23809 and JP-A-59-39400 disclose partial hydrolysates of poly (N-vinylcarboxylic acid amide).
JP-A-59-39399 and JP-A-62-74.
No. 902 and JP-A-63-218718 disclose N
-Hydrolysates of copolymers of vinyl carboxylic acid amides with other monomers are disclosed.

[0007]

SUMMARY OF THE INVENTION Grade 1 and / or 2
A polymer coagulant containing a secondary amine has good adsorptivity to sludge and has a strong effect of lowering the water content of the dewatered cake.
However, the above flocculant is easily affected by polyvalent anion salts and alkalis, and has a weak flocculating power against organic sludge containing a large amount of bicarbonate ions, such as digested sludge. In the refining method, handling of acid is dangerous, and scum may be generated by foaming. In order to improve this, even if a conventionally known iron salt or aluminum salt is added to the organic sludge for sludge conditioning, the dewatering property of the sludge is not improved, and a polymer having a primary and / or secondary amine is used. There has been a demand for a method of exerting the effect of the flocculant on a wide range of sludge.

[0008]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and as a result, have found that a water-soluble alkaline earth metal salt and vinylamine structural unit and / or
Midine structural unit is at least 35 mol% of all repeating units
The present inventors have found that an extremely excellent sludge dewatering effect is exhibited by adding a cationic organic polymer flocculant to the sludge in combination.

[0009] The invention of claim 1 of the present invention relates to a water-soluble alkaline earth metal salt and a vinylamine structural unit for organic sludge .
And / or the amidine structural unit is 35 of all repeating units.
A sludge dewatering method characterized by adding a cationic organic polymer flocculant of not less than mol% .

According to a second aspect of the present invention, an alkaline earth
After adding the metal salt, the vinylamine structural unit and / or
Or the amidine structural unit is at least 35 mol% of all repeating units.
2. The method for dewatering sludge according to claim 1, wherein said cationic organic polymer flocculant is added .

The water-soluble alkaline earth metal salt used in the present invention is a calcium or magnesium salt, and is not particularly limited. From an economic viewpoint, calcium chloride or magnesium chloride can be selected. Among them, calcium chloride is particularly preferably used. These alkaline earth metal salts are contained in an amount of 1 to 1 liter of organic sludge.
It is desirable to add a cationic organic polymer flocculant after adding and mixing 100 to 5000 mg, and then tempering.

Although it is effective to add the alkaline earth metal salt and the cationic organic polymer flocculant to the sludge simultaneously or in a mixture, it is effective to add the alkaline earth metal salt first to improve the drainage. The water content also decreases. Stirring is performed after the addition of the alkaline earth metal salt, but the purpose is to sufficiently contact the added metal salt and organic sludge to carry out the reaction, and the stirring method may use a stirring blade, It may be due to the flow in the piping.

In the present invention, the reduced viscosity means the reduced viscosity measured at 25 ° C. by dissolving a test polymer compound in 1N saline at a concentration of 0.1 g / dl.

[0014] N - vinylformamide may have alternating copolymerization ratios of acrylonitrile, easy to adjacent N- vinylformamide structural units and acrylonitrile structural units. As a result, the acrylonitrile structural unit adjacent to the vinylamine structural unit generated by the hydrolysis of the N-vinylformamide structural unit generates a cyclic amidine structural unit by intramolecular chemical modification. The amidination reaction is carried out under heating conditions of 80 to 150 ° C, preferably 90 to 120 ° C under acidic conditions.

In the present invention, a water-soluble polymer having a ratio of a cationic structural unit, which is a combination of a vinylamine structural unit and an amidine structural unit, of 35 mol% or more of all the repeating units is used. Although the performance as a sludge dehydrating agent tends to improve as the ratio of amidine structural units increases, it is impractical to convert all functional groups into amidines by a cyclization reaction. The resulting functional group also has structural units such as N-vinylformamide, vinylamine, acrylonitrile, acrylamide, and acrylic acid in the molecule. In the present invention, the cationic polymer flocculant is added and mixed in an amount of 0.2 to 2% by weight based on the suspended solids in the sludge. The polymer flocculant having an amine / amidine structure and the various acrylic polymer flocculants described above can be added in combination.

In the present invention, an oxidizing agent such as hydrogen peroxide, a preservative, a fragrance and the like can be used in combination for the purpose of deodorizing. In addition, iron salts, aluminum salts, zinc salts, and the like can be used in combination as long as the effects of the alkaline earth metal salts are not adversely affected. It is not preferable that the sludge pH is alkaline, but if the sludge pH after refining stays at 6 or less, the addition of an alkaline substance is also allowed.

[0017]

The action of the alkaline earth metal salt in the present invention is as follows.
It is presumed that the main effect is to inactivate the coagulation inhibitor such as bicarbonate ions and to increase the cohesiveness of sludge, but it is not clear.

[0018]

Next, the present invention will be described in more detail by way of examples, which should not be construed as limiting the present invention. Table 1 shows the polymers used in Examples and Comparative Examples.

[0019]

[Table 1]

(Examples 1 to 8 , Comparative Examples 1 to 6 ) Digestion and washing sludge (pH: 7.
0, solids concentration: 17800 mg / l)
In a 00 ml beaker, a predetermined amount of calcium chloride and magnesium chloride dissolved in a 10% aqueous solution was added and mixed, and then a predetermined amount of a sludge dewatering agent shown in Table 1 in the form of a 0.2% by weight aqueous solution was added. , TRITON CST
1000 r. p. m. The mixture was stirred at a rotation speed of 10 seconds. After measuring the size of the flocculated floc generated by the stirring, the flocculated sludge was transferred to a cylinder having a 60-mesh nylon filter cloth and filtered by gravity filtration.
After 2 seconds, the amount of drainage was measured. 30cm sludge after gravity filtration
A square polyethylene monofilament filter cloth (manufactured by Nippon Filcon Co., Ltd.) is sandwiched between two sheets, and this is further sandwiched between polyvinyl chloride plates having water drainage grooves, and pressed at a pressure of ² kg / cm ^2.
After pressing and dewatering for 0 seconds, the water content of the dewatered sludge cake was measured by an ordinary method. Table 2 shows the above results.

[0021]

[Table 2]

(Examples 9 to 16 and Comparative Examples 7 to 8 ) The same as Examples 1 to 8 using digested sludge (pH: 7.7, solids concentration: 23600 mg / l) from the T municipal sewage treatment plant. The test was performed by the method. Table 3 shows the results.

[0023]

[Table 3]

(Examples 17 to 19 , Comparative Examples 9 to 13 ) The same as Examples 1 to 8 using mixed raw sludge (pH: 6.0, solids concentration: 16500 mg / l) from the municipal wastewater treatment plant in the F city. The test was performed by the method. Table 4 shows the results.

[0025]

[Table 4]

[0026]

The present invention relates to a method for dewatering organic sludge, and provides an extremely excellent sludge dewatering effect by adding an alkaline earth metal salt and an organic polymer flocculant having a specific structure to the sludge in combination. Can be obtained.
The method for dewatering organic sludge of the present invention is extremely effective for dewatering sludge even for organic sludge containing a large amount of bicarbonate ions such as digested sludge. high.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-59-230700 (JP, A) JP-A-53-15277 (JP, A) JP-A-52-30777 (JP, A) JP-A-3-3 118804 (JP, A) JP-A-59-39400 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C02F 11/00-11/20

Claims (2)

(57) [Claims] An alkaline earth metal salt soluble in organic sludge and a vinylamine structural unit and / or an amidine structure.
A method for dewatering sludge, comprising adding a cationic organic polymer coagulant whose unit is at least 35 mol% of all repeating units . 2. The method according to claim 1, wherein the alkaline earth metal salt is added.
All ruamine and / or amidine structural units
High cationic organic content of at least 35 mol% of the repeating units
The sludge dewatering method according to claim 1, wherein a molecular coagulant is added .