JP2001121158A - Flocculation auxiliary for water purification treatment and production thereof and coagulation treatment and treatment apparatus thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of a novel starch based coagulant aid being perfectly safe to a human body, through it is used to water purification treatment for producing drinking water, excellent in coagulation effect, and also eliminating trouble of gelation like activated silica, and a use method of the flocculation auxiliary. SOLUTION: The coagulation aid for water purification treatment consisting of an aqueous solution is produced by stirring β-starch and caustic alkali under the condition of 12.8-13.5 pH to produce a pasty aqueous solution, and then aging it until rotational viscosity of the aqueous solution at the 3% starch concentration becomes <=50 mpa.s. As the coagulation treatment method in the water purification treatment, ferric chloride is added to raw water for purification treatment, then the aged starch aqueous solution is added under the condition of a 0.03-0.5 (starch pouring ratio/Fe Cl3 pouring ratio) ratio and stirred.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a starch-based coagulation aid suitable for water purification treatment for water supply and a method for producing the same, and a coagulation treatment method for water purification treatment using the starch-based coagulation aid and a treatment apparatus therefor. In particular, it is intended to obtain a starch-based coagulation aid having the largest coagulation action and to more efficiently perform the coagulation treatment method in the water purification treatment for obtaining clean water.

[0002]

2. Description of the Related Art In water purification treatment for tap water, only an aluminum-based inorganic coagulant (aluminum sulfate, polyaluminum chloride (PAC)) has been conventionally used. But,
The use of an inorganic coagulant alone does not form a large floc, and thus has a disadvantage that the solid-liquid separation speed in the coagulation sedimentation step and the sand filtration step is low. There is also a disadvantage that the sludge discharged from the coagulation separation step has poor sedimentation, concentration, and dewatering properties. In order to solve this problem, it is conceivable to use various synthetic polymer flocculants such as polyacrylamide in combination.However, in water treatment, there are concerns about the safety of synthetic organic polymer flocculants on humans. Not authorized. In water treatment, sodium alginate produced from kelp was used as a safe natural polymer flocculant in several places, but its coagulation promoting effect was not good, and it was very expensive Its use was not widespread.

[0003] The inventor of the present invention has advanced research on water purification treatment technology for obtaining clean water, and an aqueous starch solution obtained by gelatinizing (pregelatinizing) starch under alkaline conditions has been used as a safe coagulation aid for natural components. It has been disclosed that soda and activated silica have a much more effective coagulation effect (Japanese Patent Laid-Open No.
128955). However, in the above patent application, studies on the optimum conditions for converting starch into α-coagulant with caustic alkali were extremely insufficient.

[0004]

SUMMARY OF THE INVENTION The present invention seeks to improve the technique of the inventor's prior patent application (Japanese Patent Application Laid-Open No. 11-128555). An object of the present invention is to provide a novel starch-based flocculant which is completely safe for the human body even when used for water purification treatment for producing drinking water, has a very good flocculating effect, and has no gelling trouble such as active silica. It is something to offer. Further, in producing a starch-based coagulation aid, a method for producing an alkalized starch aqueous solution for water purification having a coagulation effect superior to that of the prior application, and a water-purification method using the starch-based coagulation aid and a treatment apparatus therefor Is provided.

[0005]

The present invention has solved the above-mentioned problems by the following means. (1) Beta starch and caustic are added at pH 12.8 to 1
After stirring under the conditions of 3.5 to produce a pasty aqueous solution, the rotational viscosity of the aqueous solution at a starch concentration of 3% was 500 mpa ·
s. A coagulation aid for water purification treatment consisting of an aqueous solution aged to s or less. (2) Beta starch and caustic were added at pH 12.8 to 1
After stirring under the conditions of 3.5 to produce a pasty aqueous solution, the rotational viscosity of the aqueous solution at a starch concentration of 3% was 500 mpa ·
s or less.

(3) Water Purification Treatment After ferric chloride is added to the raw water, the coagulation aid for water purification treatment of (1) above is used in a ratio of (starch injection rate / FeCl ₃ injection rate) of 0.03 to 0.3%. Coagulation treatment method in the water purification treatment of adding and stirring under the conditions of 5. (4) After adding ferric chloride to the raw water for the water purification treatment, the coagulation aid for water purification treatment of the above (1) was added (starch injection rate / FeC
The raw water was added at the conditions of 0.03 to 0.5 as l ₃ injection rate) ratio was introduced into the stirrer to stir, the separation of flocs in the solid-liquid separation device raw water containing the generated floc Coagulation treatment device in water purification treatment.

In water, beta starch (meaning raw starch, meaning starch in an ungelatinized state) and caustic (N
aOH or KOH) under specific starch concentration conditions and pH conditions, and aging for more than a predetermined time, it was found that a natural polymer coagulant having a very large coagulation effect and safe for the human body could be produced. . Since the same effect is obtained with both caustic soda and caustic potash, the following describes the case where caustic soda is used.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The following is a summary of new findings found in the research stage of the present invention. The pregelatinized starch means a starch which has been gelatinized and made water-soluble, and the raw starch is referred to as beta starch. Caustic soda is added to low viscosity (several mpa · s) suspension water in which β-starch is suspended in a predetermined concentration range (2 to 6%),
When H is 12.8 to 13.5, the starch particles are rapidly dissolved several minutes after the addition of the caustic soda to form a highly viscous (3% aqueous solution of starch, rotational viscosity of about 1700 mpa · s) paste-like aqueous solution. When the viscosity change of the pasty starch aqueous solution was measured over time, the viscosity rapidly decreased in about 1 hour,
The viscosity decreases to pa · s. Thereafter, the viscosity was found to decrease very slowly.

Conventionally, a polymer flocculant such as polyacrylamide has a larger flocculating effect as the viscosity of the aqueous solution at the same polymer concentration is higher. Is known to worsen. That is, it is well known that a polymer flocculant has a short elapsed time after dissolution, and that the fresher the polymer, the greater the flocculating effect. In particular, it is common knowledge that one day or more after the dissolution is used up within one day after the dissolution because the aggregation effect is deteriorated.

[0010] Surprisingly, however, the aqueous solution of pregelatinized starch with caustic alkali, which is a natural water-soluble polymer, is aged more than several hours after dissolution and has a greater viscosity than immediately after dissolution, due to the aggregation effect at the point where the viscosity is highest. The present inventor has found an interesting phenomenon that the coagulation effect at the time when the temperature is lowered is much better. This phenomenon was not previously known. As will be described in detail in Examples described later, in order to exhibit the maximum flocculating effect by adding the aqueous starch solution pregelatinized with caustic to the coagulation treatment step of the water purification treatment, the starch suspension water was pregelatinized with caustic alkali. After that, the rotational viscosity (when the starch concentration is 3%) is 500 mpa · s
It turned out to be important to use those aged until: However, the upper limit of the aging time was 6 days, and it was recognized that the coagulation effect was deteriorated when the aging time was longer than this.

There is an optimum range for the pH of the starch and caustic soda mixed aqueous solution, and it has been found that setting the pH in the range of 12.8 to 13.5 is important for producing a starch aqueous solution having an excellent coagulation effect. did. At a pH of 12.8 or less, the β starch does not become α and does not change into a paste form. When the pH was 13.5 or more, it was found that the molecular structure of the pregelatinized starch was destroyed and the molecular weight was lowered, or the aggregation effect was deteriorated. Conventionally, when producing a pregelatinized starch with an alkali, it has not been known that there is an upper limit of PH. There is an appropriate range for the injection rate of the starch coagulation aid, and the ratio (starch injection rate / ferric chloride injection rate) to raw water is 0.0
It is important to inject under conditions of 3 to 0.5. 0.5
It was found that when the ratio exceeded, part of the starch remained in the flocculated water and the potassium permanganate consumption increased. If it is less than 0.03, the floc forming effect is poor.

The method of the present invention, which has been completed based on the above findings, does not require a complicated operation for producing active silica from water glass as in the prior art, and is an expensive natural polymer flocculant such as sodium alginate. Without using
It has been found that a starch-based natural polymer flocculant that is much safer for the human body and has a much stronger floc formation-promoting action than these can be produced very easily, at low cost, and to perform an extremely effective flocculation treatment. . After injecting ferric chloride into the raw water for coagulation treatment, inject the light starch coagulation aid of the present invention, rapidly stir, and then stir with a flocculator, immediately form very large flocs, sedimentation tanks, filtration layers, etc. Can perform solid-liquid separation at high speed.

When ferric polysulfate (polyiron) or aluminum-based coagulant PAC and sodium sulfate are used together with the aqueous starch solution of the present invention, ferric chloride and the present starch are used. It was confirmed that the floc formation effect was remarkably inferior to the case where the coagulation aid was used in combination. Such a fact was not previously known. The starch aggregation aid of the present invention,
It is essential to use it together with ferric chloride. In the prior application of the present inventors, it was disclosed that the iron-based flocculant had a greater effect in combination with the starch flocculant than the aluminum-based flocculant,
It was not disclosed that among the iron-based flocculants, ferric chloride had a significantly greater combined effect than polyiron.

[0014]

The present invention will be described in detail with reference to the following examples. However, the present invention is not limited to only these examples.

Example 1 [Production of Coagulation Aid of the Present Invention (Alkaline Pregelatinized Starch Aqueous Solution) and Relationship between Aging Time and Viscosity] 30 g of powdered corn starch β-starch was added to tap water 1000
cc and stirred. In this case, the starch only disperses and does not dissolve.
When adjusted to 13.5, preferably 13.0 to 13.2, the starch gelatinized (gelatinized) after a few minutes and changed to a highly viscous transparent aqueous solution. The solution was aged while being slowly stirred, and the relationship between the aging time and the rotational viscosity was measured. The viscosity was measured using a Toki Sangyo Co., Ltd. product; B-type rotary viscometer RB80. The liquid temperature at the time of measuring the viscosity was 25 ° C. The viscosity at the time of pregelatinization by adding NaOH to the starch suspension water is 16
Although the viscosity was very high at 98 mpa · s, it was drastically reduced to 480 mpa · s after 1 hour, 278 after 2 hours, 255 after 3 hours, 238 after 6 hours, 209 m after 24 hours.
The value of pa · s is shown.

Example 2 (Aggregation treatment test) A jar test was conducted on raw water from the S waterworks at Nara prefecture. Take 500 cc of raw water into a beaker, add 15 mg / l of ferric chloride and rapidly stir at 150 rpm for 30 seconds, then add 3 mg / l of a starch coagulation aid prepared in Example 1 for each aging time. , Stirring speed 150rpm
After stirring at 2.5 m for 2.5 minutes, the mixture was slowly stirred at 50 rpm for 10 minutes. The water temperature was 26 ° C. Table 1 shows the relation of floc sedimentation speed when starch having a different aging time was added. The jar test was performed 10 times under the same conditions using pregelatinized starch having an aging time of 2 to 3 hours, the entire amount of floc was taken in a 100 cc measuring cylinder, and the sedimentation volume when sedimented for 30 minutes was 21 cc. . As shown in Table 1, the viscosity immediately after the starch suspension was pregelatinized with caustic was the highest, and the conventional concept of a polymer flocculant was considered to have the highest flocculation effect. It was recognized that the effect was poor, and rather that the mixture was aged for 1 to 2 hours or more, the viscosity was greatly reduced, and an excellent coagulation effect was exhibited after the time when the viscosity change with time became stable.

[0017]

[Table 1]

Comparative Example 1 Raw water from the S Suisuijo Nara prefecture used in Example 2 was added to a beaker.
A 100 cc sample was subjected to a coagulation test using a combination of ferric chloride and sodium alginate by a jar test. 15 ferric chloride
mg / L and rapidly stirred at 150 rpm for 30 seconds, and then sodium alginate (manufactured by Kimitsu Chemical Co., Ltd.) for 1-3 m
g / liter, and after rapid stirring for 2.5 minutes, 50 rpm
Gently with stirring for 10 minutes, and settling speed of generated floc and volume of generated floc (the jar test was performed 10 times under the same conditions,
Collect all the generated floc in a 100cc measuring cylinder,
The volume after settling for 30 minutes is measured). Table 2 shows the measurement results. Sodium alginate is a famous flocculant aid used in some water purification plants, but it was found that the floc formation effect and the condensing property were remarkably inferior to those of the present invention.

[0019]

[Table 2]

Example 3 When the starch coagulation aid of the present invention is used, how the coagulation effect (produced floc sedimentation speed) changes depending on the type of inorganic coagulant used in combination with the raw water of Example 2 The test was performed under the same jar test conditions as in Example 2. The starch aggregating agent used was aged for 3 hours after pregelatinization. Polyaluminum chloride, aluminum sulfate,
Ferric polysulfate and ferric chloride were used. The injection rate of the inorganic coagulant was 0.1 mmol / liter as Al or Fe element. The starch coagulation aid injection rate was 3 mg / liter. In addition, the floc sedimentation speed when only each inorganic flocculant was injected without adding the starch flocculant was also measured. The results are shown in Table 3. The values in parentheses indicate the sedimentation speed when the inorganic coagulant alone is added without adding the starch coagulant. From Table 3, the floc sedimentation rate without the use of the starch flocculant is the same as that of each inorganic flocculant, but the most excellent synergistic effect when the ferric chloride and the starch flocculant of the present invention are used together. Was observed.

[0021]

[Table 3]

Example 4 Raw water from the Tokyo Water Purification Plant was sampled and subjected to a flocculation test using the starch flocculation aid of the present invention. Table 4 shows the raw water quality.

[0023]

[Table 4]

(Aggregation Test Method) An agglutination test was conducted under the same jar test stirring conditions as in Example 1 to verify the effect of the method of using ferric chloride and alkali pregelatinized starch in combination according to the present invention. The alkali pregelatinized starch used was aged for 3 hours after production. In each test, the injection rate of the alkali pregelatinized starch was set to 3 mg / liter,
The injection rate of other flocculants was changed. For comparison, PA
C, ferric chloride alone, the combined use of PAC and alkali pregelatinized starch, and the combined use of ferric polysulfate and alkali pregelatinized starch were tested.

(Test Results) The results of the test are shown in the graph of FIG. FIG. 1 is a graph showing the relationship between the chemical injection rate of each flocculant and the floc sedimentation speed. In FIG. 1, alkali pregelatinized starch is indicated as “C starch”, ferric chloride is indicated as “salt iron”, and ferric polysulfate is indicated as “polyiron”. According to this graph, only when ferric chloride and alkali pregelatinized starch were used in combination, a remarkable floc-forming effect was recognized, and a surprisingly high floc sedimentation rate of 500 mm / min was obtained. As can be seen from the graph, even when PAC and alkali pregelatinized starch are used in combination, the floc sedimentation does not increase so much.
In contrast, when ferric chloride and alkali pregelatinized starch were used in combination, floc sedimentation was markedly enhanced, and 350 mm at a drug injection rate of 0.06 mol / L or more.
A floc sedimentation speed exceeding / min was obtained. In addition,
The combined use of ferric polysulfate and alkali pregelatinized starch had clearly lower floc sedimentation than the combination of ferric chloride and alkali pregelatinized starch. Therefore, it was proved that the combined use of ferric chloride and alkali pregelatinized starch had the most remarkable synergistic effect.

Example 5 A test was conducted to determine the proper addition rate of the starch aggregation aid of the present invention. 15 mg / L of ferric chloride was injected into the raw water of the water purification plant of Example 2 (consumption of 2.34 mg / L of raw water-soluble potassium permanganate) with rapid stirring, and aging time was 3 hours after 30 seconds Of the present invention was added at 1 to 15 mg / liter, and the mixture was further rapidly stirred for 2.5 minutes, gently stirred at 30 rpm for 10 minutes, sedimented floc for 5 minutes, and the supernatant water was washed with Whatman GF / B.
The solution was filtered through filter paper, and the potassium permanganate consumption of the filtrate was measured. Table 5 shows the results. (Starch / chlorinated second
Iron) The appropriate addition ratio was 0.5 or less, and it was recognized that if more than this amount, starch remained in the treated water, so that the consumption of potassium permanganate in the treated water became worse.

[0027]

[Table 5]

[0028]

According to the present invention, the following effects can be obtained. The aged starch coagulation aid of the present invention can form floc having much better sedimentation properties than the conventional alkalized starch aqueous solution (used without aging) disclosed in the prior application disclosed by the present inventors. The liquid separation speed can be greatly improved. By clarifying the optimum pH range when starch is pregelatinized with an alkali, a starch aggregation aid having good aggregation performance can be obtained with good reproducibility. By using ferric chloride and the starch flocculant of the present invention in combination, a floc having much better sedimentation is formed than when using another inorganic flocculant. Further, by setting the starch / ferric chloride injection ratio to an appropriate value, it is possible to prevent deterioration of the consumption amount of potassium permanganate in the treated water.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a chemical injection rate of each flocculant and a floc sedimentation speed in Example 4 of the present invention.

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Claims (4)

[Claims] 1. The method of claim 1, wherein the beta starch and the caustic are mixed with a pH of 1.
After stirring under the conditions of 2.8 to 13.5 to produce a pasty aqueous solution, the rotational viscosity of the aqueous solution at a starch concentration of 3% was 50%.
Coagulation aid for water purification consisting of an aqueous solution aged to 0 mPa · s or less. 2. The method according to claim 1, wherein the beta starch and the caustic are mixed with a pH of 1.
After stirring under the conditions of 2.8 to 13.5 to produce a pasty aqueous solution, the rotational viscosity of the aqueous solution at a starch concentration of 3% was 50%.
A method for producing a coagulant aid for water purification, characterized by aging it to 0 mpa · s or less. 3. The fermentation aid for water treatment according to claim 1, wherein ferric chloride is added to the raw water for water treatment treatment.
A coagulation treatment method in a water purification treatment in which FeCl ₃ is added under a condition of a ratio of 0.03 to 0.5 and stirred. 4. The fermentation aid for water treatment according to claim 1 after the addition of ferric chloride to the raw water for water treatment.
The raw water added under the condition of 0.03-0.5 as a ratio of (FeCl ₃ injection rate) is introduced into a stirrer and stirred, and the raw water containing the generated flocs is separated into flocs in a solid-liquid separator. Coagulation treatment device in water purification treatment.