JPH11114315A - Flocculant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To significantly simplify the producing method of a flocculant without causing gelation troubles in the production process of a flocculant and without causing gelation during storage. SOLUTION: This flocculant for water treatment consists of a coexistent state of a starch 3 in a aq. soln, 2 containing metal ions which produce hydroxides in water. The starch 3 is preferably α-starch and is preferably incorporated by 1 to 5% concentration. The starch 3 is mixed in a aq. soln. 2 containing metal ions which forms hydroxides.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coagulant used for coagulating various kinds of wastewater and a method for coagulating water using the same. The present invention relates to a method of coagulating water to be used, which is characterized by its coagulant composition.

[0002]

2. Description of the Related Art Coagulation is widely performed to remove suspended solids, dissolved organic substances, phosphate ions, and the like in various wastewaters. In these coagulation treatments,
Aluminum sulfate, poly aluminum chloride, sulfuric acid second
Aluminum or iron-based inorganic metal salt coagulants such as iron, ferric polysulfate, and ferric chloride are used.
Recently, titanium-based inorganic metal salt flocculants have also appeared. Since these inorganic flocculants do not form large flocs when used alone, they have the disadvantage that the solid-liquid separation speed in the flocculation-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.

[0003] For this reason, various synthetic polymer flocculants have hitherto been frequently used to promote floc formation by inorganic flocculants. However, the use of synthetic organic polymer flocculants in tap water treatment is not approved due to concerns about the safety of the coagulants. Conventionally, only PAC and sulfate bands have been used in water treatment. However, it has recently been pointed out that aluminum ions in drinking water may cause Alzheimer's disease. Studies have begun on whether to stop using and use iron-based flocculants.

[0004] In addition, the eutrophication of raw water for water treatment has progressed,
In raw water containing a large amount of algae such as microcystis,
With conventional inorganic flocculants such as PAC or sulfate bands, only flocs having extremely poor sedimentation are formed, and flocs may float up, and there is a problem that algae cannot be effectively removed. In the water treatment field, as a highly safe coagulation aid,
The use of activated silica found by Aylis was examined, but gelation troubles frequently occurred during the production of activated silica, and it was extremely difficult to stably produce activated silica, so that it was not put to practical use in Japan.

According to the Baylis method, water glass is diluted with water to form an aqueous solution having a silica concentration of 1.5%, and the pH is adjusted to 8.5 by adding sulfuric acid, followed by stirring at room temperature for 2 hours to polymerize the silica monomer. Obtaining polymerized silica, that is, activated silica ". However, recently, there has been a movement to re-evaluate activated silica.
75796 "Water treatment method and water treatment flocculant"
"Polymerized silica having an intrinsic viscosity of about twice or more the intrinsic viscosity of a silica monomer and a soluble salt of a metal capable of forming a hydroxide in water were mixed at a ratio such that the molar ratio of silicon to the metal was 2 or more. Inject and mix things into the water to be treated. ''
A coagulation treatment method using a mixed coagulant of polymerized silica (another name of activated silica) and a metal salt is disclosed.

FIG. 2 shows a method for producing a flocculant according to this technique.
In the conventional method, as shown in FIG. 2, an acidification tank 7 in which a diluted strongly alkaline water glass aqueous solution 5 and a mineral acid 6 are mixed to adjust the pH to 2 or less, and a silica monomer 8 is further converted into an alkali 9
A large-capacity polymerization tank 10 for polymerization at pH 4 for 2 to 6 hours,
A tank 13 for mixing an iron salt or an aluminum salt 12 with a polymerized silica (active silica) aqueous solution 11 flowing out of the polymerization tank 10 is indispensable. However, when the present inventor examined the present technology in detail, it was recognized that there were the following problems and it was necessary to develop a more excellent technology.

[0007] The time required for polymerizing the silica monomer to adjust the polymerized silica having the required intrinsic viscosity requires 2 to 6 hours. Therefore, it takes a long time to prepare the activated silica, and the volume of the polymerization tank is increased. Since the required polymerization time varies greatly due to subtle deviations in silica concentration, water temperature, stirring intensity, pH, etc., it is very difficult to set the polymerization time.If the polymerization time is set incorrectly, gelation of silica will occur during polymerization. (If the silica concentration is increased to 4% or more, gelling troubles are extremely likely to occur), and it cannot be used as a flocculant. If the polymerization time is insufficient, only those having a poor coagulation effect can be obtained. In addition, it takes more than one hour for an expert to measure the intrinsic viscosity,
In practice, it is not possible to control the polymerization time while measuring the limiting viscosity in the field.

[0008] Gelling of the produced flocculant tends to occur in a short time. Therefore, in order to prolong the gelation time, the concentration of the polymerized silica (active silica) must be reduced to 2 to 3% or less and the iron concentration to 1% or less.
In particular, the concentration of iron is low. Therefore, the cost of transporting and storing the flocculant from the flocculant manufacturing plant to the user increases. Since the silicon / metal ion molar ratio is as large as 2 or more, the injection rate of silica is inevitably increased and the chemical injection cost is increased, and the amount of sludge generated is increased because the added silica is changed to SS.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a flocculant which has solved the drawbacks of the prior art and a method for producing the flocculant to obtain the flocculant. It is an object of the present invention to establish a method for producing a starch-containing inorganic flocculant having various characteristics. A method for producing a flocculant which does not cause gelling trouble during the production of the flocculant. A flocculant that does not gel during storage. The production method is significantly simpler than a flocculant incorporating polymerized silica. It is another object of the present invention to provide a coagulation treatment method using the coagulant.

[0010]

The present invention has solved the above-mentioned problems by the following means. (1) A coagulant for water treatment, wherein starch is allowed to coexist in a metal ion-containing aqueous solution that forms a hydroxide in water. (2) The coagulant for water treatment according to (1), wherein the starch is a pregelatinized starch. (3) The coagulant for water treatment according to (1) or (2), wherein the starch is contained at a concentration of 1 to 5%. . (4) A method for producing a coagulant for water treatment, comprising mixing starch with an aqueous metal ion-containing solution forming a hydroxide.

FIG. 1 shows a method for producing a flocculant of the present invention. That is, as shown in FIG. 1, a predetermined amount of pregelatinized starch is stirred in a tank 1 by a stirrer 4 with a metal ion-containing aqueous solution 2 forming a hydroxide in water such as ferric, aluminum, or titanium. It has been found that a starch-containing inorganic flocculant having a large flocculating effect can be produced by a very simple operation of adding and mixing No.3.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following are points to be noted in the practice of the present invention. (A) A metal ion-containing aqueous solution that forms a hydroxide in water, for example, a ferric salt (ferric chloride, ferric sulfate, ferric nitrate, ferric polysulfate, etc.), an aluminum salt (aluminum sulfate) Or an aqueous solution of sodium aluminate or titanium salt (such as titanium chloride);
By mixing with starch, it is possible to easily produce a flocculant having an extremely large flocculating effect and having no gelling trouble and having good storage stability. (B) The use of starch which has been pregelatinized by heating or alkali-treating an aqueous solution of starch as a starch can produce a flocculant having a large flocculating effect. The pregelatinized starch is gelatinized starch, and the raw starch is referred to as beta starch. (C) If a raw starch in powder form is directly added to an aqueous solution containing metal ions, an effective coagulant cannot be produced, and it is important to add a pregelatinized starch.

(D) An extremely effective coagulant can be produced by preparing an aqueous solution of the pregelatinized starch and then adding and mixing the aqueous solution with a ferric salt or an aqueous solution of aluminum chloride. (E) Addition of sodium alginate, a well-known anionic polymer flocculant for water treatment, and synthetic organic polymer flocculant to aqueous solution containing ferric ion or aluminum ion, which is a cationic inorganic flocculant, in place of starch When trying the mixing method, the anion polymer instantaneously reacts with positively charged metal ions and gels, losing the effect of the flocculant.
Surprisingly, even when only pregelatinized starch is added to and mixed with an acidic aqueous solution such as a ferric salt or aluminum salt which is a cationic inorganic coagulant, an effective coagulant is obtained without gelation.

(F) Since starch is an easily perishable organic substance, there is concern that the obtained flocculant may have poor storage stability. However, even if the flocculant is stored at 40 ° C. for one month, the flocculant does not deteriorate. Not allowed. It was found that the reason for this was that microorganisms could not propagate because the pH of the flocculant was strongly acidic. (G) No gelling trouble during storage such as the conventional polymerized silica-containing inorganic flocculant is observed. This is because starch does not have a gelling phenomenon unlike polymerized silica.

According to the method of the present invention, which has been completed based on the above findings, it is possible to provide a strong floc without the complicated operation of producing active silica by providing a water glass acidification tank and a monomer silica polymerization tank as in the prior art. It has been found that a starch-containing inorganic flocculant having a formation promoting action can be produced very easily and reliably. When the coagulant of the present invention is poured into raw water for coagulation treatment and stirred in a stirring tank, very large flocs are quickly formed, and solid-liquid separation can be performed at a high speed in a sedimentation tank or the like. In the case of a starch-containing ferric coagulant, the coagulant does not contain aluminum which may cause Alzheimer's disease, and is particularly suitable for water treatment. In the case of water treatment, the appropriate injection rate of the coagulant of the present invention is often about 1 to 10 mg / liter as a metal element similarly to the conventional inorganic coagulant.

[0016]

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 starch-containing iron-based flocculant) Powdered raw starch (corn starch) was added in an amount of 50 g to 500 cc of tap water, and heated to boiling with stirring to dissolve the starch. This was added and mixed with 500 g of an aqueous ferric chloride solution (20% FeCl ₃ concentration), and then the pH was adjusted to obtain a starch-containing ferric chloride aqueous solution (pH 1.0, starch content 5%, FeCl ₃ concentration 10%). %) About 1050 g were obtained.

Example 2 (Production of a starch-containing aluminum-based flocculant) 500 cc of an aqueous solution of pregelatinized starch (produced by Oji Cornstarch Co., Ltd.) (starch concentration: 10%) was added to an acidic aqueous solution of aluminum sulfate (Al
₍₂ O ₃ concentration: 8%) and mixed, and then adjusted to pH 2.0 to obtain a starch-containing aluminum-based flocculant.

Example 3 (Aggregation test and investigation of coagulant preservability) Kaolin was added to tap water to prepare a suspension having a turbidity of 100 °.
The various coagulants prepared in 2 were added and a jar test was performed. The condition of the jar test was a stirring rotation speed of 150 rpm90.
Seconds, 50 rpm 90 seconds. PH after coagulant injection is 6
It was fixed. The water temperature was 24 ° C. For comparison, a coagulation test using aluminum sulfate and ferric chloride was performed. The coagulant injection rate was 2, 4, 6, 8 mg / Fe or Al
Four conditions of liter were used.

The floc generation time during the jar test and the floc particle size after 60 seconds during slow stirring were measured. One minute after the end of the jar test, the turbidity of the supernatant water was measured. Table 1 shows the results. The floc particle size was indicated according to the following criteria. E: 0.2 mm or less, D: 0.2 to 0.5 mm, C: 0.5 to 2 mm, B: 2 to 5 mm, A: 5 mm or more. As shown in Table 1, as compared with the case where ferric chloride or aluminum sulfate was injected, the starch-containing flocculant could clearly show the aggregation promoting effect at all injection rates. When the starch-containing coagulant was both iron-based and aluminum-based with an injection rate of 4 mg / liter or more, extremely large flocs were formed, and during slow stirring, the flocs settled at the bottom and changed into pellets while rolling. .

[0020]

[Table 1]

[0021]

EFFECTS OF THE INVENTION The flocculant of the present invention can form a floc having a large particle diameter, which has much better sedimentation properties than a conventional inorganic flocculant. Since starch is a food, it can be safely used for water treatment. Since the starch-containing iron-based flocculant does not contain aluminum, aluminum suspected of causing Alzheimer's disease does not increase in the treated water and is very suitable for treated water. The water-glass acidification tank and silica polymerization tank, which were required for the production of the conventional iron-based flocculant containing polymerized silica, are no longer required, and the measurement of the intrinsic viscosity of the polymerized silica is also unnecessary, making the flocculant manufacturing process extremely simple. Can be There is no gelation trouble during the production and storage of the flocculant. The metal concentration in the flocculant can be made higher than before, and the active ingredient concentration in the flocculant can be increased.
Therefore, transportation cost and storage cost of the flocculant are reduced. Long-term storage is possible because starch does not rot.

[Brief description of the drawings]

FIG. 1 is a schematic view showing one example of a method for producing a flocculant of the present invention.

FIG. 2 is a view showing a flow sheet of a typical example of a conventional method for producing a flocculant.

[Explanation of symbols]

 Reference Signs List 1 tank 2 metal ion-containing aqueous solution 3 starch 4 stirrer 5 water glass aqueous solution 6 mineral acid 7 acidification tank 8 silica monomer 9 alkali 10 polymerization tank 11 polymerized silica aqueous solution 12 metal salt 13 mixing tank

Claims (4)

[Claims] 1. A coagulant for water treatment, wherein starch is coexistent in a metal ion-containing aqueous solution forming a hydroxide in water. 2. The coagulant for water treatment according to claim 1, wherein said starch is pregelatinized starch. 3. The coagulant for water treatment according to claim 1, wherein the starch is contained at a concentration of 1 to 5%. 4. A method for producing a coagulant for water treatment, comprising mixing starch with an aqueous solution containing metal ions forming a hydroxide.