JP2019147154A - Rice wash wastewater treatment method - Google Patents

Abstract

To provide a method for treating rice wash wastewater that can be treated without diluting high-concentration rice wash wastewater and that can reduce the amount of inorganic coagulant used.SOLUTION: A method for treating rice wash wastewater is characterized in that: after adding aluminum sulfate or polyaluminum chloride as a coagulant to rice wash wastewater with a SS value of 1,000 to 10,000 mg/L, a polymer of dimethylaminoethyl methacrylate methyl chloride quaternary salt or a copolymer of dimethylaminoethyl (meth) acrylate methyl chloride quaternary salt and acrylamide is used as a cationic polymer flocculant.SELECTED DRAWING: None

Description

  The present invention relates to a method for treating washed rice wastewater.

  Washed rice wastewater generated in a brewing process, large-scale rice cooking factory or non-washed rice milled rice production process is highly concentrated sewage with an SS value of 6,000 mg / L and a BOD value of about 4,000 mg / L. It is wastewater and needs some kind of treatment.

  As an example of a method for treating washed rice wastewater, there is known a method in which calcium chloride is added to washed rice wastewater, and then suspended matter is coagulated and separated (Patent Document 1). This method has an advantage that the amount of treated water and the capacity of the waste liquid tank can be reduced as much as possible because it can be treated without diluting the high-concentration washed rice waste water.

  By the way, the above method requires a considerable amount of calcium chloride. That is, in the Example, 20 mL of 5 wt% calcium chloride aqueous solution is added to 2 L of washed rice wastewater, and the amount of calcium chloride per 1 L of washed rice wastewater is 500 mg / L and the amount of calcium is 180 mg / L. Moreover, as an example of a conventional coagulation precipitation method, an example in which a polymer coagulant is added after adding 200 ppm of a coagulant: PAC (polyaluminum chloride) to washed rice waste water is described. Although a problem lacking in properties has been pointed out, specific types of polymer flocculants are not illustrated, and the effectiveness is not clear.

Japanese Patent Laid-Open No. 4-190891

  The present invention has been made in view of the above circumstances, and its object is to provide other processing methods that can be processed without diluting high-concentration rice washing wastewater in the same manner as the above-described method. It is in the point that contributes to the conversion. Another object of the present invention is to provide a method for treating washed rice wastewater in which the type of inorganic coagulant is not limited. Still another object of the present invention is to provide a method for treating washed rice wastewater that can reduce the amount of inorganic coagulant used.

  In order to achieve the above object, the present inventor has conducted extensive studies on a method for treating rice washing wastewater in which a polymer flocculant is added after adding a coagulant to rice washing wastewater. When the organic coagulant is used together with the inorganic coagulant or the inorganic coagulant as the agent, and further the cationic polymer flocculant is used, the knowledge that the above object can be achieved is obtained, and the present invention is completed. It came.

  That is, the gist of the present invention is that after adding aluminum sulfate or polyaluminum chloride as a coagulant to washed rice wastewater having an SS value of 1,000 to 10,000 mg / L, dimethylaminoethyl methacrylate methyl chloride quaternary salt The present invention resides in a method for treating rice washing wastewater characterized by using a polymer or a copolymer of dimethylaminoethyl (meth) acrylate methyl chloride quaternary salt and acrylamide as a cationic polymer flocculant.

  According to the present invention, reduction of the amount of agglomerated sludge and settling time, which are the above-mentioned problems, are achieved.

  Hereinafter, the present invention will be described in detail.

<Rice wash water>

  In the present invention, as the rice washing waste water, for example, the rice washing waste water having a high SS value and BOD value can be used as in the rice washing waste water described in the prior art. Usually, the SS value is 1,000 to 10,000 mg / L, the BOD value is 1,000 to 10,000 mg / L, and the COD value is 1,000 to 7,000 mg / L.

<Inorganic coagulant>
The inorganic coagulant is not particularly limited, and those generally used can be used. For example, aluminum sulfate (sulfate band), polyaluminum chloride (PAC), ferric chloride, polyferric chloride, lime, etc. can be used. Of these, sulfate bands and PAC are particularly preferred. The inorganic coagulant neutralizes the charge on the surface of the suspended solids in the washed rice wastewater, and causes coagulation by a coagulation action that aggregates particles dispersed in the solvent by van der Waals force (intermolecular attractive force). The inorganic coagulant is sometimes called an inorganic flocculant.

<Organic coagulant>
The organic coagulant is not particularly limited, and those commonly used can be used. For example, polyamine, diallyldimethylammonium chloride polymer, dialkylaminoalkyl methacrylate alkyl chloride quaternary salt polymer, dialkylaminoalkyl acrylate alkyl chloride quaternary salt copolymer with acrylamide, and the like.

  Since the organic coagulant as described above is a polyelectrolyte having a large number of cationic groups in the molecule, it has a charge neutralizing action similar to that of the inorganic coagulant. Due to the high charge density, its coagulation has the advantage of being much greater than that of inorganic coagulants. In addition, it has the advantage of increasing the coagulation of suspended solids due to the adsorption action of the polymer chain. Especially in high SS such as washed rice wastewater, this effect becomes remarkable due to the close distance between the suspensions, and the inorganic coagulant. Compared to, the effect is significantly reduced. In this respect, it is separate from the so-called polymer flocculant described later. That is, the polymer flocculant aggregates particles dispersed in a solvent by an aggregating action that collects small aggregates to form large aggregates (floc). And the intrinsic viscosity is 7 dL / g or more normally. On the other hand, the organic coagulant has a lower molecular weight than the polymer flocculant, and is preferably 5 dL / g or less.

<Polymer flocculant>
The polymer flocculant used in the present invention is preferably a cationic polymer flocculant. The cationic polymer flocculant can be obtained by using various known monomers as raw materials and polymerizing them. Examples thereof include a polymer of dimethylaminoethyl methacrylate methyl chloride quaternary salt and a copolymer of dimethylaminoethyl (meth) acrylate methyl chloride quaternary salt and acrylamide. In general, an anionic polymer flocculant is used for the coagulation sedimentation treatment. However, at high SS such as the rice washing wastewater of the present invention, the ionic balance of the coagulated rice washing wastewater still remains anionic. In particular, a cationic polymer flocculant is suitable. Furthermore, it is preferable that the cationic structural unit is 10 to 100 mol% with respect to the total monomer units from the viewpoint of the aggregation and precipitation rate and turbidity. The cationic constituent unit is more preferably 20 to 60 mol% with respect to the total monomer units. This is presumably because hydrogen bonding by the amide group of acrylamide is the main factor of aggregation.

Examples of the polymerization method of the cationic polymer flocculant include precipitation polymerization, bulk polymerization, dispersion polymerization, and aqueous solution polymerization. As an example, a manufacturing method using an aqueous solution polymerization method will be described below.
First, a predetermined amount of dimethylaminoethyl (meth) acrylate methyl chloride quaternary salt, acrylamide, and ion-exchanged water are weighed and adjusted to a predetermined temperature, and then charged into a heat-insulating container that can be sealed. Next, the dissolved oxygen is replaced with nitrogen gas, and chemicals such as a polymerization initiator and a chain transfer agent are added. As the polymerization initiator, known general azo initiators, redox initiators, and the like can be used.
As the polymerization proceeds, the polymerization temperature rises, but after the temperature reaches its peak, it is aged for 1 hour, and the polymer gel is taken out from the reaction vessel. The polymer gel is shredded with a meat chopper and dried at a temperature of 80 ° C. with a blower dryer. The dried polymer is pulverized with a pulverizer to a particle size of about 0.5 to 1 mm to obtain a cationic polymer flocculant.
A solid acid can be added to the cationic or amphoteric polymer flocculant in the present invention in order to reduce viscosity or improve reactivity. As the solid acid, sulfamic acid is generally used.

  The addition of each of the above-mentioned chemicals is preferably carried out under mechanical stirring with a separate tank, but after adding the coagulant to the rice washing wastewater in the wastewater line and guiding it to the coagulation tank, the polymer coagulant is added. It is also possible to adopt a method of adding or a method of adding the coagulant and the polymer flocculant to the waste water in the rice washing waste water line by shifting the addition position. In the case of line mixing, it is necessary that the turbulent flow state is sufficient, and when it is insufficient, installation of a line mixer or the like is also effective.

  The inorganic coagulant and the organic coagulant may be added at the same time or separately, and the order of addition is arbitrary, but in the case of washed rice wastewater, it is preferable to add the organic coagulant following the addition of the inorganic coagulant. . Usually, a powdery organic coagulant or polymer flocculant is dissolved in water and used as an aqueous solution having an appropriate concentration (for example, an aqueous solution having a concentration of 0.1 to 0.3% by mass). Depending on the coagulant and polymer flocculant, the applicable pH range may be determined in order to maximize its function. In this case, appropriate pH adjustment should be performed before adding the drug according to a conventional method. I do.

  The amount of each chemical added varies depending on the BOD, COD, and turbidity of the washed rice wastewater. The addition amount of the molecular flocculant is usually 0.1 to 10 mg / L. In the present invention, the amount of inorganic coagulant used can be reduced by using an organic coagulant together with the inorganic coagulant, but the amount of inorganic coagulant reduced depends on the amount of organic coagulant used. Therefore, the usage ratio of both is appropriately determined in consideration of the total amount. In addition, the solid-liquid separation of the floc that has been agglomerated can be performed according to a conventional method.

  EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to a following example, unless the summary is exceeded. In the following examples and comparative examples, the used rice washing waste water, chemicals, and measurement items are as follows.

<Rice wash water>
BOD: 3,220 (mg / L), CODMn: 2,400 (mg / L), TOC: 639 (mg / L), SS: 2,000 (mg / L), pH 5.0 washed rice wastewater did.

<Drug>
(1) Organic coagulant: Organic coagulant described in Table 1. The organic coagulant was used as a 0.3% by weight aqueous solution.
(2) Inorganic coagulant: sulfate band, PAC (polyaluminum chloride)
(3) Cationic polymer flocculant: Polymer flocculants described in Table 1. The cationic polymer flocculant was used as a 0.3 wt% aqueous solution, and the anionic polymer flocculant was used as a 0.1 wt% aqueous solution.

<Measurement item>
(1) Intrinsic viscosity of organic coagulant and polymer flocculant:
Intrinsic viscosity was measured based on a conventional method using a Ubbelohde dilution type capillary viscometer in a 1N sodium nitrate aqueous solution at a temperature of 30 ° C. 107).
(2) Flock diameter:
The floc diameter of the aggregated floc was measured visually and the average value was taken as the floc diameter. (3) Settling time:
A predetermined amount of the polymer flocculant is added, and after stirring for a predetermined time, stirring is stopped. And the time until the produced | generated aggregation floc settles in the bottom of a 500 mL beaker was measured.
(4) Supernatant BOD: Measured based on JIS K 0102-21 and -32.3. (5) Supernatant COD: Measured based on JIS K 0101.
(6) Supernatant turbidity: measured based on JIS K 0101.
(7) Supernatant TOC: Measured based on JIS K 0101.

Examples 1-4:
Collect 300 mL of raw water (washed rice waste water) in a beaker, add the kind and amount of inorganic coagulant shown in Table 2 while stirring at 150 rpm, mix for 1 minute, and then adjust the pH adjuster (1 mol / L water) Sodium hydroxide aqueous solution) was added to adjust the pH to 7, and the mixture was further stirred and mixed for 1 minute. Next, the types and amounts of polymer flocculants shown in Table 2 were added, and the mixture was stirred and mixed in the same manner as described above. After stirring for 2 minutes, the stirring was stopped, the floc particle size and sedimentation time were measured, and further 2 minutes later, the supernatant of the treatment liquid was collected from a depth of 3 cm from the liquid surface with a syringe. Items were measured. The results are shown in Table 2.

Examples 5-16:
In the said Example, after adjusting to pH7, except having added the organic coagulant of the kind and quantity shown in Table 2, it operated similarly to the said Example and measured each said item. The results are shown in Table 2.
Comparative Examples 1-7:
In the said Example, except having added the kind and quantity of polymer flocculants shown in Table 2, it operated similarly to the said Example and measured each said item. The results are shown in Table 2.

表１中の構成成分の略号は下記を示す。
ＤＭＣ：ジメチルアミノエチルメタクリレート塩化メチル４級塩
ＤＭＥ：ジメチルアミノエチルアクリレート塩化メチル４級塩
ＡＡＭ：アクリルアミド
ＡＡ：アクリル酸

The abbreviations of the constituent components in Table 1 are as follows.
DMC: dimethylaminoethyl methacrylate methyl chloride quaternary salt DME: dimethylaminoethyl acrylate methyl chloride quaternary salt AAM: acrylamide AA: acrylic acid

Table 2 shows the following.
In Examples 1-16, compared with Comparative Examples 1-7, the favorable aggregation performance was shown and the turbidity of the treated water was favorable. In Examples 5-16, the usage-amount of an inorganic coagulant is reduced significantly compared with Examples 1-4. Further, Examples 7 to 11 in which the cationic structural unit of the cationic polymer flocculant is in a preferred range are superior in terms of sedimentation of the aggregated floc as compared with Examples 5 and 6 (there are many cationic structural units). Compared to Example 12 (having few cationic structural units), the turbidity of treated water is also excellent.

Claims (4)

  After adding aluminum sulfate or polyaluminum chloride as a coagulant to rice washing wastewater having an SS value of 1,000 to 10,000 mg / L, a polymer of dimethylaminoethyl methacrylate methyl chloride quaternary salt or dimethylaminoethyl (meta ) A method for treating rice washing wastewater, characterized by using a copolymer of acrylate methyl chloride quaternary salt and acrylamide as a cationic polymer flocculant.   The method for treating rice wash wastewater according to claim 1, wherein the BOD value of the rice wash wastewater is 1,000 to 10,000 mg / L.   The method for treating rice wash wastewater according to any one of claims 1 to 2, wherein the COD value of the rice wash wastewater is 1,000 to 7,000 mg / L. The method for treating washed rice wastewater according to any one of claims 1 to 3, wherein an organic coagulant is used together with an inorganic coagulant as the coagulant.