JPH0380523B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a flocculant composition containing a powdered anionic polymer flocculant having a carboxyl group and an amide group, particularly an anionic flocculant composition suitable for sludge dewatering. [Prior art] In order to increase the solubility of the anionic polymer flocculant, a powdered base such as a carbonate and a powdered acid are blended with the anionic polymer flocculant, and the mixture is foamed during dissolution to form the flocculant. A method with improved dispersibility has been proposed (Japanese Patent Application Laid-open No. 61636/1983). In addition, in order to dissolve an anionic polymer flocculant and a cationic polymer flocculant in one liquid, a method has been proposed in which an acid is dissolved together with these flocculants (Japanese Patent Application Laid-Open No. 1983-1999).
216707). [Problems to be solved by the invention] The anionic polymer flocculant mixed with a powdered base and acid improves the dispersibility by foaming, but does not significantly increase the solubility of the flocculant. However, the concentration could only be increased to about 0.4% by weight. In addition, for those that simultaneously dissolve anionic polymer flocculants and cationic polymer flocculants and acid, depending on the target sludge, the cationic polymer flocculant may react with the sludge when the composition is added to the sludge. Previously, there was a problem that the electric charge of the sludge was not sufficiently neutralized due to the reaction with the anionic polymer flocculant, making it difficult to reduce the water content. [Means for Solving the Problems] This invention is intended to solve the above problems, and by blending a powdered anionic polymer flocculant and a powdered acid, anionic polymer flocculation is achieved. An object of the present invention is to provide an anionic flocculant composition that can increase the solubility of an agent, lower the viscosity of an aqueous solution to form a highly concentrated aqueous solution, and improve the flocculating properties of sludge and the like. The present invention comprises a composition of a powdered anionic polymer flocculant having a carboxyl group and an amide group, and a powdered acid,
The molar ratio of amide groups is 35/65 or less, and the amount of the acid dissolves the composition in water and increases the concentration of flocculant pure.
An anionic flocculant composition characterized in that the amount is such that the pH of the aqueous solution is 4 or less when the amount is 0.4% by weight. The anionic polymer flocculant in the present invention is a powdered anionic polymer flocculant having a carboxyl group and an amide group and a carboxyl group/amide group molar ratio of 35/65 or less, such as polyacrylamide or Partial hydrolysates of polymethacrylamide, copolymers of acrylamide or methacrylamide with acrylic acid or methacrylic acid, copolymers of acrylamide or methacrylamide with acrylic acid or methacrylamide and acrylamide methylpropanesulfonic acid, etc. , intrinsic viscosity [η] 30℃ 1N-NaCl is 5 (dl/
g) The above are preferred, and these can be used alone or in combination. Powdered acids include sodium hydrogen sulfate, sodium dihydrogen phosphate, boric acid, sulfamic acid, maleic acid, malic acid, malonic acid, succinic acid, tartaric acid, oxalic acid, citric acid, fumaric acid,
Examples include adipic acid and glutaric acid, and these can be used alone or in combination. The anionic flocculant composition of the present invention is a powdered composition containing the anionic polymer flocculant and an acid, and the amount of acid is determined by dissolving the composition in water to obtain a pure anionic polymer flocculant. This is the amount that makes the pH of the aqueous solution 4 or less when the concentration is 0.4% by weight. The anionic flocculant composition of the present invention is directly added to water and dissolved, and used as an aqueous solution. The aqueous solution is used by dissolving the flocculant at a pure concentration of 0.4% by weight or more. At a concentration of 0.4% by weight or more, the pH of the aqueous solution will be 4 or less, and in this state, the carboxyl group of the anionic flocculant becomes H-type and has less dissociative properties, less ion repulsion and less molecular spread. The viscosity of the solution decreases, and the coagulant can be dissolved at a high concentration of 1% by weight or more as a pure flocculant. Generally, the allowable concentration of a flocculant solution is determined by the viscosity of the solution, and from the viewpoint of operability of flocculation treatment, it is appropriate that the viscosity of the solution is 1000 cPs or less, preferably 600 cPs or less, but the anionic flocculant composition of the present invention Because of its low viscosity, it satisfies the above conditions even with a pure concentration of about 1% by weight. Further, since the above-mentioned flocculant composition has a small molecular spread, the dispersion rate is significantly higher than the dissolution rate, and the dispersibility is good. The above aqueous solution does not exhibit anionic properties when dissolved at a high concentration, but when added to sludge or wastewater to be treated, the acid is diluted and the pH increases, which causes the carboxyl group of the flocculant to dissociate. and acts as an anionic flocculant. In the present invention, the molar ratio of carboxyl group/amide group of the anionic polymer flocculant is limited because if the above molar ratio exceeds 35/65, the carboxyl group and amide group will react due to intermolecular association. Generates insoluble matter, which can be removed by adding an aqueous solution to sludge, etc.
This is because it does not dissolve even after the pH increases. The composition of the present invention can be used as a flocculant for general coagulation treatment of sludge, sewage, etc., but is sometimes suitable for use in sludge dewatering. When used as a sludge dewatering agent, it is possible to dehydrate inorganic sludge such as coagulated sedimentation sludge by adding only the anionic flocculant composition, and it can be used to dehydrate organic sludge such as biologically treated sludge. After neutralizing the electric charge of the sludge with a cationic flocculant, dewatering can be carried out by adding an aqueous solution of an anionic flocculant composition. When flocculating sludge or sewage using only an anionic flocculant composition, the treatment can be carried out in the same manner as in the conventional method, but even if the amount of pure flocculant added is less than in the conventional case, flocculation is possible. The effect can be increased. Examples of sludge that can be treated in combination with a cationic flocculant include anaerobic digested sludge of human waste, aerobic digested sludge of human waste, human waste septic tank sludge, human waste digested desorbed liquid, sewage, and activated sludge treatment of various industrial wastewater. Examples include surplus sludge, sewage primary sedimentation tank sludge, human waste, and flocculated sludge generated during tertiary treatment of sewage, etc. Examples of the cationic flocculant include inorganic metal salts such as iron chloride, iron sulfate, aluminum chloride, aluminum sulfate, polyferric chloride, and polyferric sulfate, and cationic polymer flocculants. Among these, cationic polymer flocculants include (a) homopolymers of aminoalkyl acrylate or aminoalkyl methacrylate or copolymers with acrylamide or other monomers, (b) containing acrylamide or methacrylamide as a structural unit. Mannitz modified or Hofmann decomposed products of polymers,
Examples include (c) polyamide polyamine, (d) polyvinylimidazoline, (e) polyethyleneimine, (f) polydialkyl diallylammonium salt, and (g) chitosan, and these can be used alone or in combination. . Among the above, (a) in particular is used as a combination containing 10 to 50% by weight of inorganic salts such as sodium chloride, sodium sulfate, ammonium sulfate, sodium hydrogen sulfate, calcium chloride, magnesium chloride, etc. that do not exhibit alkalinity when made into an aqueous solution. is desirable. When adding these cationic flocculants, the sludge and flocculant are stirred after addition so that they come into sufficient contact. In particular, when a cationic polymer flocculant is added as a cationic flocculant, it is preferable to perform the first stirring with a strong enough force to prevent the formation of flocs with a diameter exceeding 2 mm.This will neutralize the electric charge of the sludge. be harmonized. After the first stirring, an aqueous solution of the anionic flocculant composition is added and a second stirring is performed to form a floc. The stirring intensity at this time may be the same as the normal stirring level used for sludge dewatering, but in some cases, stronger stirring may be used. When a cationic flocculant is added to the sludge and the first stirring is performed, the anion charges on the sludge surface are neutralized, and some of the sludge coagulates due to adsorption and crosslinking. At this time, if the first stirring is strong stirring, neutralization of charges will be the main focus. Next, when an anionic flocculant composition is added, the carboxyl groups of sodium acrylate and other components in the composition become in the H-form (carboxylic acid) state in the state of an aqueous solution, and the viscosity decreases due to intramolecular association. Because it is in a condensed state, it has good dispersibility when added to sludge.
It has good reactivity with the cationic flocculant adsorbed on the sludge surface and the cationic groups of the unreacted cationic flocculant present in the liquid. When anionic polymer flocculants are added to sludge, the PH of M alkalinity components etc.
The carboxyl group gradually dissociates and becomes anionic due to substances that increase the carbon content and polyvalent cations such as iron ions, which become adsorbed and crosslinked as anionic groups to strengthen the flocs. . In the conventional method of adding a cationic polymer flocculant and performing strong stirring to neutralize the electric charge of the sludge, then adding an anionic organic polymer flocculant and performing slow stirring to flocculate, the anionic polymer flocculant is As a molecular flocculant, it is not practical because low water content cannot be obtained unless it contains 50 mol% or more of sodium acrylate, which has a high anionic charge density, in terms of reactivity, but in that case it does not contain an amide group. As a result, the flocs became weak against stirring, making it impossible to obtain stability, and the amount added was sometimes increased. However, when the anionic flocculant composition of the present invention is initially added to sludge, it is in a condensed state due to intramolecular association, so the apparent anionic charge density increases and acts effectively, which gradually causes dissociation. Therefore, when stirred, the molecules enter a state of association, and the flocs are adsorbed to cover the flocs over a wide area, producing a powerful floc that is resistant to agitation. Furthermore, since the anionic polymer flocculant has many amide groups, it has a strong adsorption and crosslinking effect on sludge. In the above sludge dewatering treatment, the amount of cationic flocculant added is generally 5 to 30% by weight in the case of an inorganic flocculant, and 0.3 to 4% by weight in the case of a cationic polymer flocculant (in both cases). vs. SS) is fine.
In addition, the amount of the anionic flocculant composition added is generally 0.2 to 0.2 as the pure content of the anionic polymer flocculant.
It is sufficient to add about 2% by weight (based on SS), and good dehydration properties can be obtained even if the amount added is smaller than the conventional case where no acid is blended. The floc produced by the above method is dehydrated using a dehydrator in the same manner as in the conventional method. As the dehydrator used for dehydration, conventionally used dehydrators such as a centrifugal dehydrator, belt press type dehydrator, screw press, filter press, etc. can be used. [Effects of the Invention] According to the present invention, since a powdered anionic polymer flocculant and a powdered acid are blended, the solubility of the anionic polymer flocculant is increased and a low viscosity, high concentration aqueous solution is prepared. In addition, it is possible to improve flocculation treatment properties, efficiently treat sludge, etc. with a low amount of flocculant, lower the water content of sludge, and increase the SS recovery rate. [Example] Examples will be described below. Example 1 A powdered anionic flocculant composition containing the partial hydrolyzate of polyacrylamide shown in Table 1 and sodium hydrogen sulfate (sodium sulfate in the case of the comparative example) was prepared with a purity of 0.4% by weight. PH when dissolved in pure water and stirred with a stirrer for 2 hours so that
and the viscosity were measured and shown in FIGS. 1 and 2. Furthermore, the pH and viscosity when the dissolved concentration of the anionic flocculant is changed are shown in FIGS. 3 and 4.
In Figures 1 to 4, the compounding ratio indicates the weight ratio,
The dissolved concentration is the weight percent of the pure anionic polymer flocculant.
shows.

[Table] From the results shown in Figures 1 and 2, it is clear that when an aqueous solution becomes PH4 or lower due to the addition of an acid, the viscosity decreases rapidly, and even if an inorganic salt that does not exhibit acidity is added to the aqueous solution, the viscosity decreases rapidly. It can be seen that the viscosity decrease is not so large. Furthermore, the results shown in FIGS. 3 and 4 show that the flocculant composition of the present invention has a purity of 1
It can be seen that the viscosity is usable even when dissolved to about % by weight. Example 2 Sludge was dehydrated using the flocculants shown in Table 2. First, a mixed raw sludge of initially settled sludge and excess activated sludge from a sewage treatment plant [PH6.0, SS2.3% by weight.
VSS72% (vs. SS), fiber content 14% (vs. SS)], A
After adding the chemicals, stir vigorously for 2 minutes at 300 rpm in a stirring tank equipped with two blades until the flocs have a diameter of 2 mm or less, then add D chemicals, feed the slurry to a centrifugal dehydrator, and centrifuge. Agglomerated flocs were generated and dehydrated by stirring in a dehydrator, and the water content of the dehydrated cake, the amount of dewatering processed, and the SS recovery rate were measured.
The results are shown in Table 3. As a comparative example, the results when chemical B was added instead of chemical D and when chemical C was added instead of chemical D are also shown. The centrifugal dehydrator was operated at the same differential speed and orifice plate position.

【table】

【table】

[Table] In addition, when chemical A was mixed with sodium sulfate at a ratio of 4:1 (weight ratio) and subjected to the same treatment, the amount of sludge treated was 110 kg-ds with the same amount of chemical added (0.7/0.6). /h, the cake moisture content was 79.7%, and the SS recovery rate was 99%. Example 3 Mixed sludge of surplus activated sludge of human waste oxidation treatment method and tertiary treatment sludge [PH7.0, SS1.5-1.7% by weight,
Table 4 shows the results of the same test as in Example 2 for VSS 75 to 78% (vs. SS) and fiber content of 5% (vs. SS) or less.

【table】

[Table] Example 4 Pressurized floating scum of paper wastewater [PH6.2, SS0.9
~1.1% by weight, VSS 58~61% (vs. SS), fiber content 13
D chemical is added to the sludge obtained by dehydrating ~19% (vs. SS)], and the sludge is fed to a rotary screen.
Stir at 30 rpm to generate agglomerated flocs,
Gravity filtration was performed. Next, the flocs were fed to a belt press type dehydrator to obtain a dehydrated cake. For comparison, the same treatment was carried out using chemical C. Both results are shown in Table 5.

[Table] Example 5 Mixed raw sludge of first settled sludge and excess activated sludge from a sewage treatment plant [PH5.4, SS2.0%, VSS74% (vs.
SS), fiber content 13% (vs. SS)] was added with polyferric sulfate (E) as a metal salt and stirred for 30 seconds at 500 rpm (peripheral speed 2 m/sec) using two flat blades to form fine flocs. After that, add chemical D and further
Stir at 500 rpm for 30 seconds. Thereafter, the floc diameter was measured, and a portion of the cake that remained on the cake was passed through a Buchner funnel, taken between two filter cloths, and dehydrated by pressing at a pressing pressure of 0.5 kg/cm ² to measure the water content. For comparison, using C drug instead of D drug,
I did the same process. Both results are shown in Table 6.

[Table] From the above results, compared to the comparative example, the sample of Example had the same or lower addition amount, the cake moisture content was also the same or lower, the processing amount and recovery rate were improved, and the dehydration effect was stable. It can be seen that this shows that

[Brief explanation of drawings]

1 to 4 are graphs showing the results of Example 1.

Claims (1)

[Scope of Claims] 1. Consists of a composition of a powdered anionic polymer flocculant having a carboxyl group and an amide group and a powdered acid, the molar ratio of the carboxyl group/amide group being 35/65 or less. and the amount of the acid is such that when the composition is dissolved in water and the pure concentration of the flocculant is 0.4% by weight, the pH of the aqueous solution is 4 or less. Composition. 2 Anionic polymer flocculants include partial hydrolysates of polyacrylamide or polymethacrylamide, copolymers of acrylamide or methacrylamide and acrylic acid or methacrylic acid, and copolymers of acrylamide or methacrylamide and acrylic acid or methacrylamide and acrylamide. The anionic flocculant composition according to claim 1, which is one or more selected from copolymers with methylpropanesulfonic acid. 3 The anionic polymer flocculant has an intrinsic viscosity [η]
The anionic flocculant composition according to claim 1 or 2, which has a 1N-NaCl content of 5 (dl/g) or more at 30°C. 4 Powdered acids include sodium hydrogen sulfate, sodium dihydrogen phosphate, boric acid, sulfamic acid, maleic acid, malic acid, malonic acid, succinic acid, tartaric acid, oxalic acid, citric acid, fumaric acid, adipic acid, and The anionic flocculant composition according to any one of claims 1 to 3, which is one or more types selected from glutaric acid.