JP4761500B2 - Inhibitor of calcium carbonate scale by slaked lime suspension and method of inhibiting calcium carbonate scale - Google Patents

Description

  The present invention uses sludge flocculation as a sludge flocculating agent for general industrial wastewater treatment plants and public sewage treatment plants, particularly when sludge flocculation is performed using iron salt and slaked lime suspension in combination. The present invention relates to a scale inhibitor and a scale suppression method for suppressing a calcium carbonate scale derived from a slaked lime suspension in a slaked lime suspension preparation tank, a liquid feeding pipe, and the like in the treatment process.

  Conventionally, slaked lime is widely used as a flocculant for sludge in general industrial wastewater treatment plants and public sewage treatment plants because it is inexpensive, has high safety, and has little impact on the environment. For example, the sewage collected from the area is treated with a predetermined chemical treatment, microbial treatment, etc., and then this treated water is added to polyiron chloride and slaked lime suspension to agglomerate and precipitate, and then centrifuged with a centrifugal dehydrator. The sludge is incinerated or landfilled after solid-liquid separation, and the separated treatment liquid is sterilized and pH adjusted and discharged into the river.

  In general, the slaked lime suspension is prepared by reacting quick lime (calcium oxide) with water (digestion reaction) or by dissolving slaked lime in water. The prepared slaked lime suspension is stored in a storage tank, and is sequentially sent to a target location by a transfer pipe using a liquid feed pump. However, the prepared slaked lime suspension reacts with carbon dioxide in the air to form calcium carbonate to form calcium carbonate in the slaked lime suspension storage tank, transfer pipe, centrifugal dehydrator filter and drain pipe. Scale adheres and deposits, causing various obstacles. For example, the calcium carbonate scale on the inner wall of the slaked lime suspension storage tank adheres and deposits, and if this peels off, it clogs the transfer pump and causes pump failure, or the calcium carbonate scale adheres, deposits and accumulates in the transfer pipe. Cause blockage of the piping.

  Therefore, the calcium carbonate scale has been periodically removed manually by the conventional method, but the efficiency is low and this is not preferable. Further, as a scale inhibitor and a scale suppression method for calcium carbonate, ethylenediaminetetraacetic acid 2-4 sodium salt (EDTA 2-4Na), 1-hydroxyethylidene-1, 1-diphosphonate sodium (HEDP), 2-phosphono-1 Although a method using a phosphonic acid compound such as sodium 2,2, butanetricarboxylate (PBTC) is known, it does not exhibit a sufficient effect. Moreover, it may adversely affect the sludge aggregating action of polyiron chloride used as a sludge aggregating agent, which is not preferable. In addition, since adhesion occurs in the piping when transferring lime milk (calcium carbonate), a coil is wound around the piping for transferring lime milk, and electricity is conducted to this coil to prevent scale adhesion. (A kind of magnetic field treatment: AC magnetic field treatment) is already known, and a method of preparing a slaked lime suspension using water subjected to AC magnetic treatment (see Patent Document 1) has also been proposed. A satisfactory improvement effect cannot be obtained. Therefore, the slaked lime suspension prevents the calcium carbonate scale from adhering and accumulating in the slaked lime suspension preparation tank, the inner wall of the transfer pipe, the centrifugal dehydrator, the centrifugal dehydrator filter, and the drain pipe without losing the coagulation sedimentation effect. Suspensions of calcium carbonate scale and methods for inhibiting the scale are strongly desired.

JP 2003-165722 A

  The present invention has been made in view of such circumstances, and affects the sludge aggregation effect of slaked lime suspension that is frequently used as a sludge coagulant for general industrial wastewater treatment plants and public sewage treatment plants. There is also provided a scale inhibitor and a scale control method for preventing calcium carbonate scale from adhering and accumulating in a slaked lime suspension preparation tank, transfer pipe, centrifugal dehydrator, centrifugal dehydrator filter, drain pipe, etc. Objective.

To achieve the above object, the present inventors have as a result of intense research on how the preparation of slaked lime suspension, acrylic acid and 2-acrylamido-2-methylpropane sulfonic acid is in a specific ratio as a structural unit The present inventors have found that the copolymer and / or water-soluble salt thereof is effective for suppressing the calcium carbonate scale derived from the slaked lime suspension, and have completed the present invention.

That is, the invention according to claim 1 is an inhibitor of calcium carbonate scale by the slaked lime suspension in the sludge flocculation treatment step using the slaked lime suspension, and includes acrylic acid and 2-acrylamido-2-methylpropane. A copolymer comprising sulfonic acid as a structural unit, and acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid in a molar ratio of 99.3: 0.7 to 80:20 and / or water-soluble salt thereof It is a calcium carbonate scale inhibitor by the slaked lime suspension characterized by containing.

The invention according to claim 2 is a method for inhibiting calcium carbonate scale by the slaked lime suspension in the sludge agglomeration treatment step using the slaked lime suspension, wherein acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid are used. As a structural unit, and a copolymer of acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid in a molar ratio of 99.3: 0.7 to 80:20 and / or a water-soluble salt thereof is slaked lime. It is a method for suppressing calcium carbonate scale by slaked lime suspension, characterized by being added to the suspension.

  By the calcium carbonate scale inhibitor and the scale suppression method of the present invention, the calcium carbonate preparation tank, the transfer pipe, the centrifugal dehydrator filter, the centrifugal dehydrator filter and the calcium carbonate derived from the slaked lime suspension without affecting the sludge aggregation The scale is prevented from adhering and accumulating in the drainage pipe for a long period of time, and the conventional removal of calcium carbonate scale is greatly reduced, not only reducing the work cost but also stable sludge. It contributed to the improvement of work by bringing about coagulation and sludge dehydration.

The present invention uses a slaked lime suspension as a coagulant for sludge in a sludge agglomeration treatment process of a general industrial wastewater treatment plant or a public sewage treatment plant. A calcium carbonate scale inhibitor and a calcium carbonate scale inhibitor that suppress adhesion and accumulation in equipment in the sludge agglomeration treatment process, wherein acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid are constituent units. and then, a specific copolymer composed at a ratio of and / or inhibitors of calcium carbonate scale by slaked lime suspension containing the water-soluble salts, and the sludge using slaked lime suspension as sludge flocculant By adding the copolymer and / or water-soluble salt thereof to the coagulation treatment step, the calcium carbonate produced in the treatment step is derived from the slaked lime suspension. A method of inhibiting Lumpur.

  In the present invention, the target scale is a calcium carbonate scale mainly composed of calcium carbonate produced by a reaction between calcium hydroxide in slaked lime suspension and carbon dioxide in the air, and this is accompanied by calcium hydroxide. Includes scale.

  The sludge agglomeration treatment process in the present invention, as is usually done in general industrial wastewater treatment plants and public sewage treatment plants, drains and sewage collected from the area / region to be treated with a predetermined chemical treatment, microorganisms In this step, the slaked lime suspension is added to the treated water after the treatment or the like to cause aggregation. For example, a preparation tank for preparing a slaked lime suspension, a transfer pipe for transferring the slaked lime suspension, a flocculation tank for coagulating by mixing the slaked lime suspension and the treated water, and a solid-liquid separation of water to be treated containing the aggregates The centrifugal dehydrator and its peripheral equipment that separates into sludge and treated water, the filtrate storage tank separated by solid-liquid separation with the centrifugal dehydrator, the filtrate discharge pipe, and the filtrate are sterilized and pH adjusted This includes the discharge piping until it is discharged into the river and the peripheral equipment that performs the treatment. Usually, sludge is dried and incinerated or landfilled.

  The slaked lime suspension in the present invention is not particularly limited, and is a general aqueous suspension of calcium hydroxide, which is dispersed / suspended in calcium hydroxide dissolved in water and water in the form of fine particles. It is an aqueous suspension of calcium hydroxide in a state where turbid calcium hydroxide is mixed. Specifically, there is a method of obtaining a water suspension as slaked lime (calcium hydroxide) by reacting quick lime (calcium oxide) with water, and a method of obtaining a slaked lime suspension by dispersing slaked lime in water, The method is also acceptable. Although the density | concentration of slaked lime suspension is suitably determined according to a use condition, Usually, it is 1 to 20 weight%.

The inhibitor of calcium carbonate scale derived from the slaked lime suspension in the present invention (hereinafter referred to as “scale inhibitor of the present invention”) is composed of acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid (unit: Hereinafter referred to as “AMPS”) as a structural unit, and the acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid are in a molar ratio of 99.3: 0.7 to 80:20 And / or a calcium carbonate scale inhibitor containing a water-soluble salt thereof (hereinafter referred to as “copolymer of the present invention”). Examples of the water-soluble salt of the copolymer of the present invention include completely neutralized or partially neutralized sodium, potassium, ammonium and complex salts thereof.

In the copolymer of the present invention, the ratio of acrylic acid and AMPS which are constituent units is a copolymer containing 99.3: 0.7 to 80:20, preferably 95: 5 to 85:15. If the molar ratio of acrylic acid to AMPS is outside this range, the effects of the present invention may not be sufficiently exhibited. The weight average molecular weight of the copolymer is 500 to 30,000, preferably 1,000 to 20,000. The range of the average molecular weight is obtained from the viewpoint of the scale suppression effect, and even if outside this range, there is a scale suppression effect, but no significant improvement in the scale suppression effect is observed.

  The method for producing the copolymer of the present invention is not particularly limited, and can be obtained by a known method. For example, it can be obtained by adding an alkali metal hydroxide aqueous solution to an aqueous solution of acrylic acid and AMPS, heating to 80 to 90 ° C., dropping a polymerization initiator and polymerizing. In this case, each component of acrylic acid and AMPS may be polymerized in a free state, but these can also be subjected to a polymerization reaction as a sodium salt, potassium salt or ammonium salt. Examples of the polymerization initiator include peroxides such as sodium persulfate, chlorine peroxide, and butyl hydroperoxide, and azo compounds such as azobisisobutyronitrile. Preferred polymerization initiators are hydrogen peroxide and persulfate. Although the usage-amount of a polymerization initiator changes with kinds of polymerization initiator to be used, in hydrogen peroxide, it is 0.5-10 mol% with respect to the monomer whole quantity, Preferably it is 1-5 mol%. As the polymerization solvent, water is most preferable, but organic solvents such as alcohols and dioxane can also be used. The heating temperature during the polymerization is preferably 80 to 90 ° C. When polymerization is performed at a low temperature, an unreacted monomer may remain and may not be preferable.

  In addition, other scale inhibitors conventionally used, for example, EDTA and water-soluble salts thereof, polymaleic acid and water-soluble salts thereof, polyacrylic acid and water-soluble water thereof, as long as the effects of the scale inhibitor of the present invention are not impaired. , Phosphonates such as PBTC and HEDP, and the like, and the present invention is not limited thereto.

  The method for suppressing calcium carbonate scale derived from the slaked lime suspension in the present invention (hereinafter referred to as “the scale suppressing method of the present invention”) is used in the sludge aggregation treatment process of general industrial wastewater treatment plants and public sewage treatment plants. In this method, the copolymer of the present invention is added to suppress generation and adhesion of calcium carbonate scale derived from the slaked lime suspension used in the step.

  The addition amount of the copolymer in the scale suppression method of the present invention is appropriately determined depending on the conditions of the process using the slaked lime suspension, the water quality of the target aqueous system, the situation of the calcium carbonate scale, the degree of demand for improvement of the scale, However, the copolymer of the present invention is usually 0.05 to 10% by weight, preferably 0.1 to 5% by weight, based on the slaked lime content in the slaked lime suspension. is there. When the addition amount of the copolymer of the present invention is lower than 0.05% by weight, the effect of the present invention may not be sufficiently obtained. When it exceeds 10% by weight, the effect of the present invention can be obtained. However, the improvement in effect is small, and it is often not preferable from an economic point of view.

  The addition location of the copolymer of the present invention is usually a location where calcium carbonate scale is generated, a location where calcium carbonate scale adheres, and an upstream portion thereof. For example, there are addition to a storage tank after preparation of slaked lime suspension, injection to a transfer pipe of slaked lime suspension, addition to sludge immediately before entering a sludge dewatering device, and the like.

  The method of using the copolymer of the present invention is not particularly limited, and may be appropriately selected and determined depending on the situation. Usually, the copolymer is diluted to 1 to 50% by weight with water and used. The The means for adding the copolymer of the present invention is not particularly limited, but is usually added using a chemical injection pump.

  The addition method of the copolymer of the present invention is a method of adding a single point to a specific addition site, a method of adding multiple points divided into a plurality of locations, a continuous addition method of continuously adding, or an addition at regular intervals There are intermittent addition methods, etc., which can be appropriately selected according to various situations.

In the scale suppression method of the present invention, the copolymer of the present invention and other scale inhibitors conventionally used, such as EDTA, polymaleic acid and water-soluble salts thereof, Acrylic acid and its water-soluble salt, polyAMPS and its water-soluble salt, maleic acid-acrylic acid copolymer and its water-soluble salt, phosphonates such as PBTC and HEDP, etc. may be used in combination. It does not add.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

[Scale inhibitor used in Examples]
-Copolymer 1: Acrylic acid-AMPS molar ratio 80:20 copolymer (molecular weight 10,000)
-Copolymer 2: Acrylic acid-AMPS molar ratio 85:15 copolymer (molecular weight 20,000)
Copolymer 3: Acrylic acid-AMPS molar ratio 90:10 copolymer (molecular weight 3,000)
Copolymer 4: Acrylic acid-AMPS molar ratio 95: 5 copolymer (molecular weight 8,000)
-Copolymer 5: acrylic acid-AMPS molar ratio 99.3: 0.7 copolymer (molecular weight 10,000).

[Scale inhibitor used in comparative examples]
Copolymer 6: acrylic acid-AMPS molar ratio 73:27 copolymer (molecular weight 10,000)
-Copolymer 7: acrylic acid-acrylamide copolymer molar ratio 50:50 (molecular weight 20,000)
PAA: polyacrylic acid (molecular weight 20,000)
HEDP: 1-hydroxyethylidene-1, 1-diphosphonate sodium ["Briquest ADPA60A" (trade name), manufactured by Rhodia Japan]
PBTC: sodium 2-phosphono-1,2,4-butanetricarboxylate [“Berkulen 650” (trade name), manufactured by Great Lakes Chemical].

[Scale suppression test 1 of aqueous slaked lime solution]
In a public sewage treatment plant, the sewage collected from the area is treated with the prescribed chemical treatment, and then the treated sewage is coagulated and precipitated with polyiron chloride and slaked lime suspension, and separated into solid and liquid by a centrifugal dehydrator. The sludge was incinerated or landfilled, and the separated treatment liquid was further discharged into the river after chemical treatment and pH adjustment. Specifically, referring to FIG. 1, the slaked lime suspension used is prepared by dispersing slaked lime with water to a concentration of 1% by weight (pH: 12.7, dissolved calcium concentration: 1,080 mg / L). , Stored in the storage tank 1, introduced into the centrifugal dehydrators 10 , 11 through the transfer pipes 4 , 5 , mixed with the treated sewage 16, subjected to coagulation sedimentation and solid-liquid separation of the treated sewage, and sludge 12, 13 and drainage 14 and 15 were processed separately. However, dehydrated and discharged water of slaked lime suspension and sludge [pH: 11.3, M alkalinity (mg / L-CaCO ₃ ): 1,620, calcium hardness (mg / L-CaCO ₃ ): 4,480] Because of its strong alkalinity, the scale of calcium carbonate accumulates on the inner wall of the storage tank, the inner wall of the transfer pipe, the centrifugal dehydrator filter, and the inner wall of the discharge pipe from the centrifugal dehydrator in about 4 months. It was. For example, the calcium carbonate scale attached to the inner wall of the storage tank may peel off, causing damage to the slaked lime suspension transfer pump, or the calcium carbonate scale attached to the inner wall of the transfer pipe will reduce the diameter of the transfer pipe and transfer the slaked lime suspension. Decrease in volume, accumulation of calcium carbonate scale on the filter of the centrifugal dehydrator greatly reduces the dehydration efficiency, and sufficient sludge dehydration cannot be obtained. In addition, the calcium carbonate scale attached to the inner wall of the discharge pipe narrows the diameter of the discharge pipe. As a result, troubles such as clogging of drainage from the centrifugal dehydrator occurred. Therefore, a 1 wt% slaked lime suspension was collected from the public sewage treatment plant and used as a test solution to conduct a scale inhibition test as follows.

Add 100 ml of the test solution (slaked lime aqueous solution) to a 300 mL Erlenmeyer flask, add a predetermined amount of scale inhibitor, set it on a shaker without opening the stopper, and shake at a rate of 30 times / minute for 24 hours. . Next, precipitates of calcium carbonate generated in the test solution were No. The solution was filtered through 6 filter papers, and the calcium concentration (mg / L) of the filtrate was measured by the EDTA titration method. Based on the measurement results, the calcium carbonate precipitation inhibition rate (%) was calculated and evaluated by the following formula. It is preferable that the calcium carbonate precipitation inhibition rate (%) is higher. The results are shown in Table 1.
Calcium carbonate precipitation inhibition rate (%) = [(A−B) / (1080−B)] × 100
A: Calcium concentration of filtrate when adding scale inhibitor (mg / L)
B: Calcium concentration in the filtrate when no scale inhibitor is added (mg / L)

上記の結果より、本発明のアクリル酸−ＡＭＰＳ（モル比８０：２０〜９９．３：０．７）共重合体が、消石灰水溶液中に生じる炭酸カルシウムスケールの抑制に有効であることが分かる。

From the above results, it can be seen that the acrylic acid-AMPS (molar ratio 80:20 to 99.3: 0.7) copolymer of the present invention is effective in suppressing the calcium carbonate scale generated in the slaked lime aqueous solution.

[Scale suppression test 2 of slaked lime aqueous solution]
In the public sewage treatment plant described in the scale suppression test 1 of the slaked lime aqueous solution, the transfer pipes 4 and 5 for introducing a 1% by weight concentration of slaked lime suspension from the storage tank 1 into the treated sewage in the centrifugal dehydrators 10 and 11, Each of the chemical injection pumps 6 and 7 was injected with 0.1% by weight (against slaked lime) of the scale inhibitor, and solid-liquid separation was performed by ordinary centrifugal dehydration. After about 4 months, the accumulation state of the calcium carbonate scale on the inner walls of the transfer pipes 4 and 5 , the filters of the centrifugal dehydrators 10 and 11 and the discharge pipes 14 and 15 of the centrifugal dehydrator was visually observed and evaluated. Moreover, the influence on the aggregation effect of the slaked lime suspension by addition of the scale inhibitor in the meantime was also evaluated. The standard of evaluation is as follows, and the results are summarized in Table 2.
(Evaluation of scale adhesion)
○: There is almost no scale adhesion.
Δ: A little adhered to the scale (a level where the scale is partially adhered and the maximum adhesion thickness is less than 1 mm and can be judged as no problem).
X: Scale is clearly attached (attachment thickness: 1 mm or more).
(Influence on aggregation effect)
None: No effect on sludge aggregation.
Yes: There is an effect (the effect is that the aggregated sludge mass is small, the strength of the aggregated sludge is weak, etc.)

本発明のアクリル酸−ＡＭＰＳ共重合体（実施例１、２）により４ヶ月間、移送配管４、５の内壁、遠心脱水機１０、１１のフィルター、遠心脱水機の排出配管１４、１５の内壁への炭酸カルシウムのスケールの付着、蓄積がほとんどなく、しかも消石灰による凝集への影響もなく、本発明のアクリル酸−ＡＭＰＳ共重合体が消石灰懸濁液由来の炭酸カルシウムスケールの抑制に有効であることが分かる。

The inner wall of the transfer pipes 4 and 5 , the filter of the centrifugal dehydrators 10 and 11, and the inner walls of the discharge pipes 14 and 15 of the centrifugal dehydrator for 4 months by the acrylic acid-AMPS copolymer of the present invention (Examples 1 and 2). The acrylic acid-AMPS copolymer of the present invention is effective in suppressing calcium carbonate scale derived from slaked lime suspensions, with little adhesion and accumulation of calcium carbonate to the surface and no influence on flocculation by slaked lime. I understand that.

It is the schematic of coagulation sedimentation of the sewage treated water by slaked lime suspension.

Explanation of symbols

1: 1% slaked lime suspension storage tank 2, 3: transfer pump 4, 5: transfer pipe 6, 7: scale inhibitor injection pump 8, 9: scale inhibitor storage tank 10, 11: centrifugal dehydrators 12, 13 : Sludge 14 (centrifugated), 15: Discharged water (centrifugal) 16: Sewage treated water

Claims (2)

In the sludge aggregation treatment step using slaked lime suspension, the calcium carbonate scale inhibitor by the slaked lime suspension, comprising acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid as structural units , the acrylic A slaked lime suspension characterized in that the acid and 2-acrylamido-2-methylpropanesulfonic acid contain a copolymer in a molar ratio of 99.3: 0.7 to 80:20 and / or a water-soluble salt thereof. Inhibitor of calcium carbonate scale by suspension. In the sludge agglomeration treatment step using slaked lime suspension, a method for inhibiting calcium carbonate scale by the slaked lime suspension, comprising acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid as constituent units , the acrylic Adding a copolymer of acid and 2-acrylamido-2-methylpropanesulfonic acid in a molar ratio of 99.3: 0.7 to 80:20 and / or a water-soluble salt thereof to the slaked lime suspension. A method for suppressing calcium carbonate scale by a slaked lime suspension.

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