JPH0788478A - Wastewater treatment method - Google Patents

Abstract

PURPOSE:To carry out wastewater treatment efficiently by a flocculating and precipitating method in which polymethacrylic acid in a prescribed wt.% based on the content of polyvinyl alcohol is added to wastewater whose pH is adjusted to be a prescribed pH value and polyvinyl alcohol is flocculated and precipitated. CONSTITUTION:Wastewater is adjusted to be pH 3.5-6.5 and polymethacrylic acid in 0.1-400wt.% based on the content of polyvinyl alcohol(PVA) is added to the wastewater. Consequently, PVA at a low concentration in the wastewater is reacted with polymethacrylic acid to produce PVA-polymethacrylic acid complex, which is a water-insoluble precipitating complex, and to flocculate and precipitate the complex. In the case pH is lower than 3.5, even if the complex is produced, the complex does not have a water-insoluble structure. Also, in the case pH is 6.5 or higher, polymethacrylic acid becomes an alkaline salt and the water-insoluble complex is hardly produced, though that depends on the concentration of PVA in the wastewater.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wastewater treatment method containing polyvinyl alcohol.

[0002]

2. Description of the Related Art Polyvinyl alcohol (hereinafter referred to as PVA) is widely used as a warp sizing agent, various binders, adhesives, surface treatment agents for paper and cloth, hard finishing agents, etc. Not known as a water-soluble polymer with excellent film strength and toughness. Depending on the field of use, PVA used once may be used again after being dissolved in water. For example, when desizing a woven fabric with warp glue, it is necessary to re-dissolve it in water at the time of a recycling process in order to reuse paper or nonwoven fabric. The activated sludge method is generally used as a method for treating PVA dissolved in these wastewaters, but it requires treatment with a specific assimilating bacterium, resulting in high treatment cost and a wide treatment area. is necessary. As another wastewater treatment method, the coagulation-sedimentation method is generally used, but since there is no agent that coagulates and precipitates PVA in a thin concentration of 1% or less,
The current situation is that it cannot be processed. The coagulation-sedimentation method is also very difficult for wastewater treatment of aqueous emulsions using PVA as a protective colloid agent, such as vinyl acetate emulsions, acrylic emulsions, and ethylene-vinyl acetate copolymer emulsions.

[0003]

DISCLOSURE OF THE INVENTION The object of the present invention is to use a coagulating sedimentation method, which has hitherto been impossible to be used as a method for treating wastewater containing PVA, to make the PVA cheaper and more efficient. The present invention provides a wastewater treatment method containing

[0004]

DISCLOSURE OF THE INVENTION As a result of intensive studies in view of the present situation, the present inventors have found that polymethacrylic acid is used as a method for treating PVA in wastewater by a coagulation sedimentation method.
The present invention has found a method for treating wastewater containing PVA, which is characterized by adding 0.1 to 400% by weight to the content of A to coagulate and precipitate polyvinyl alcohol. That is, the polymethacrylic acid used in the present invention reacts with a very dilute concentration of PVA in the waste water to form a PVA-polymethacrylic acid complex, which produces a water-insoluble precipitate, which separates PVA from water. The present invention has been found to be possible and has led to the present invention.

In order to form a complex of polymethacrylic acid and PVA and effectively separate PVA, the pH in the waste water is adjusted.
Is 3.5 to 6.5, and preferably 4.0 to 6.0. When the pH is less than 3.5, more strong acid is present than polymethacrylic acid, and even if a complex is formed, the insoluble structure of water cannot be taken and separation is often insufficient. When the pH is higher than 6.5, polymethacrylic acid becomes an alkaline salt, which makes it difficult to form a water-insoluble complex, depending on the concentration of PVA in the wastewater. As a method for adjusting the pH, a method generally used in wastewater treatment may be used. The timing of pH adjustment is not particularly limited, but it is preferable to add it before or at the same time as polymethacrylic acid is added. However, after forming a water-insoluble complex of PVA and polymethacrylic acid, the complex does not break even if the pH value is out of the above range, and the PVA does not change to be water-soluble. Can be taken freely.

The polymethacrylic acid used in the present invention is preferably a homopolymer of methacrylic acid, and in some cases, it may be a copolymer with a small amount of another monomer. However, the copolymerization ratio of the other monomer is preferably 10 mol% or less. The molecular weight of polymethacrylic acid is not particularly limited, but the number average degree of polymerization is 100 to 10,000, and preferably 200 to 2,000. When the molecular weight of polymethacrylic acid is less than 100, it is difficult to form a strong complex with PVA, and when it is more than 10,000, it is difficult to produce polymethacrylic acid, and it is difficult to handle it in an aqueous solution, thus forming a complex. The speed will also be very slow. The use form of polymethacrylic acid is not particularly limited, and may be a solid state, a fine powder, an aqueous solution, or one adsorbed on another carrier, etc., but generally it is fixed. Add a solution having a concentration. PV of polymethacrylic acid
The amount of addition to A is 0.1 to 4 with respect to the content of PVA.
It is 00% by weight, and more preferably 10 to 200% by weight. When the amount of polymethacrylic acid added is less than 0.1% by weight, it cannot be used because it does not form a water-insoluble complex, and even when it is more than 400% by weight, it is a strong water-insoluble complex. Cannot be used because it is difficult to generate.

The PVA in the waste water is not particularly limited, and any PVA can be treated. For example, as PVA, a PVA having a polymerization degree of 100 to 10,000 and a saponification degree of 20 to 100 mol%, further, unmodified PVA, carboxyl group-modified PVA, sulfonic acid-modified PVA, cation-modified PVA, and PV having a hydrophobic group introduced therein.
A and various other modified PVA are the subject of the present invention. Further, not only PVA alone but also an aqueous emulsion using PVA as a protective colloid agent, for example, vinyl acetate emulsion, acrylic emulsion, ethylene-vinyl acetate copolymer emulsion, etc., is treated by the coagulating sedimentation method of the present invention. Can be taken. For these emulsions, the amount of polymethacrylic acid added is
PV contained not in amount based on weight concentration of emulsion
It is necessary to add it to the amount of A, and it is necessary to add 0.1 to 400% by weight to the content of PVA for treatment. However, in general, the amount of PVA in the emulsion is often unknown, and it is usually 5 to the solid content of the emulsion.
The optimum addition amount may be 50% by weight.

The wastewater treatment method of the present invention is carried out for the purpose of separating a PVA from water by forming a water-insoluble complex by the reaction between PVA in the wastewater and polymethacryl acid. The concentration of PVA and polymethacrylic acid, the content of PVA and polymethacrylic acid, other contaminants in the waste water, and other water-insoluble complexes formed due to various other factors may become smaller and sedimentation may be slower. In some cases, a larger composite may be obtained by using a commonly used inorganic flocculant together. Examples of the inorganic coagulant that can be used in the present invention include aluminum sulfate (sulfuric acid band), polyaluminum chloride (PAC), aluminum chloride, ferric chloride, polyferric sulfate, ferric sulfate,
Ferrous sulfate etc. are mentioned. These inorganic coagulants are generally used in an aqueous solution, but in the case of the present invention,
Not only an aqueous solution but also a solid state inorganic coagulant may be used. The inorganic coagulants may be used alone or in combination of two or more. The inorganic coagulant is preferably added after the reaction product of PVA and polymethacrylic acid in the waste water is formed. However, the pH of the waste water can be adjusted by using an aqueous solution of these coagulants, and the order of addition is not particularly limited. Furthermore, in order to make the water-insoluble complex containing PVA into larger particles and to efficiently separate it from water, a polymer flocculant can also be used depending on the situation. As the polymer flocculant, sodium polyacrylate, polyacrylamide, a partial hydrolyzate thereof,
Alternatively, a cation group-introduced product, polyethylene oxide or the like is used. In general, it is often used as an aqueous solution and rarely added as a solid, but in the case of the present invention, not only an aqueous solution but also an inorganic coagulant in a solid state may be used. The polymer flocculants may be used alone or in combination of two or more.

As an apparatus for treating waste water, an apparatus which is generally used can be used, and it is not necessary to provide a new mechanism. Hereinafter, a general processing apparatus and a general processing method will be described, but the present invention is not limited thereto. A continuous flocculation apparatus usually used conventionally comprises a mixing tank equipped with a pH meter and a quick stirrer, and a flocculation tank equipped with a slow stirrer. The mixing tank is equipped with a metering pump that supplies a fixed amount of pH adjusting solution, and the coagulation tank is equipped with a metering pump that supplies a fixed amount of an aqueous solution of polymethacrylic acid and, in some cases, an inorganic coagulant or polymer coagulant supply pump. Has been. Waste water containing PVA (including emulsion of PVA as protective colloid) is metered by a metering pump. The pH adjustment liquid has a constant pH under the control of the pH meter.
Are fed and mixed until. This waste water is then sent to a flocculation tank where a fixed amount of polymethacrylic acid is fed to form a water-insoluble complex. If necessary, a fixed amount of an inorganic coagulant or a polymer coagulant is added to grow larger floc. The agglomerated flocs thus produced are further supplied to a settling tank, a floating separation tank, a concentration screen or the like, if necessary, to separate the agglomerated flocs. Not only this continuous treatment device, but also a method of performing batch treatment in a single tank may be used. In addition to the method of adding polymethacrylic acid in the coagulation tank, after mixing in the mixing tank, liquid is fed to the coagulation tank. It may be a method.

[0010]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. Unless otherwise specified in the examples, "%" and "parts" are based on weight.

Example 1 Waste water containing PVA having a COD of 165 to 205 mg / l was treated with a continuous treatment device comprising a mixing tank having a pH meter and a rapid stirring device, a coagulation tank having a slow stirring device, and a precipitation tank. Wastewater treatment was performed. The mixing tank is further equipped with a quantitative pump capable of quantitatively supplying the pH adjusting liquid, and the aggregation tank is provided with a quantitative pump capable of supplying a 10% aqueous solution of polymethacrylic acid having a degree of polymerization of 1260, an aqueous solution of an inorganic flocculant and a polymer flocculant. There are three metering pumps that can be supplied. The treated water treated in this coagulation / separation step is sent to the settling tank.
The pH of the inflowing wastewater was 7.2, and an aqueous solution of sulfuric acid band was used as the pH adjusting liquid supplied to the mixing tank, and the flow rate was controlled by a pH meter so that the pH of the wastewater was 5.0. As the polymer flocculant provided in the flocculation tank, an anionic polymer flocculant "Aron Floc" (manufactured by Toagosei Co., Ltd.) was used. Tables 1 and 2 show the amount of chemicals used and the inflow water quality and treated water quality in the coagulation separation process. By this treatment, PVA
And polymethacrylic acid produced water-insoluble complex flocs, which coagulated and settled at the bottom of the settling tank.

Comparative Example 1 The same treatment as in Example 1 was carried out except that polymethacrylic acid was not used in Example 1. The results are shown in Tables 1 and 2. PVA when polymethacrylic acid is not used
Did not aggregate and precipitate, and almost no reduction in COD was observed.

Example 2 In treating the wastewater of Example 1, the pH was adjusted to 4.5 with sulfuric acid water, and 320 mg / l of polymethacrylic acid was used, and no other coagulant was added. When the treatment was carried out in the same manner as in No. 1, the complex floc of PVA and polymethacrylic acid was slightly small, but coagulated and precipitated without problems. The results are shown in Tables 1 and 2.

Example 3 After adjusting the pH of the wastewater of Example 1 to 5.3 with sulfuric acid water,
Treatment was performed in the same manner as in Example 1 except that polymethacrylic acid was 160 mg / l, iron chloride was 70 mg / l as the inorganic coagulant, and the polymer coagulant used in Example 1 was 1.30 mg / l. It was The results are shown in Tables 1 and 2.

Example 4 Ethylene-vinyl acetate copolymer emulsion using PVA as a protective colloid (Kuraray Co., Ltd., OM # 400)
The drainage of 0) was performed under the treatment conditions of Table 1 in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0016]

[Table 1]

[0017]

[Table 2]

[0018]

According to the present invention, PVA can be produced inexpensively and efficiently from a dilute aqueous solution of PVA which has been impossible in the past.
Can be precipitated.

Claims (1)

[Claims] 1. The pH of the wastewater is adjusted to 3.5 to 6.5,
A method for treating waste water containing polyvinyl alcohol, comprising adding 0.1 to 400% by weight of polymethacrylic acid to the content of polyvinyl alcohol to coagulate and precipitate the polyvinyl alcohol.