JP6287594B2 - Aggregation processing method and aggregation processing apparatus - Google Patents

Description

  The present invention relates to a coagulation treatment method and a coagulation treatment apparatus, and in particular, in a first reaction tank upstream of a reaction tank provided in two stages, a trivalent iron-based inorganic flocculant is added to the waste water for coagulation treatment, The present invention relates to a coagulation treatment method and apparatus for stably obtaining high-quality coagulation treated water after reducing the required amount of water treatment coagulation chemical in a method of further coagulation treatment in a second reaction tank at the latter stage. The present invention also relates to a water treatment method and apparatus for recovering water by further performing reverse osmosis separation treatment on the flocculated water obtained by the flocculation method and apparatus.

  Conventionally, reverse osmosis (RO) membrane separation treatment or RO membrane separation treatment after biologically treating water to be treated has been widely adopted for water recovery from river water and various wastewaters. When RO membrane separation treatment is performed, in order to reduce the contamination of the RO membrane, the turbidity component (fine particle component) in the water to be treated is removed and the polymer substance (biopolymer) dissolved in the water Pretreatment by agglomeration and solid-liquid separation is performed to remove water.

That is, biopolymers that are biometabolites, including microgels, exist in a dissolved state in water obtained by biological treatment of various wastewaters, water supplied from lake water, and dam lakes. This biopolymer is a high-molecular substance that has a molecular weight of 10,000 to 10,000,000, although the abundance ratio as total organic carbon in water is small. When water is recovered by desalting with an RO membrane, the RO membrane Difficult to diffuse from the surface, it concentrates and adheres on the membrane surface, causing problems such as a decrease in the permeation flux of the membrane.
For this reason, when performing RO membrane separation treatment of water containing biopolymers such as biologically treated water, it is necessary to agglomerate and remove the biopolymer together with particulate contaminants that cause RO membrane contamination.

In general, an inorganic flocculant is used for the agglomeration treatment. However, in the case of removing a biopolymer, a trivalent iron-based inorganic flocculant is used as compared with an aluminum-based inorganic flocculant such as polyaluminum chloride or a sulfuric acid band. Is superior in terms of the agglomeration effect.
The main reason is that the polysaccharide, which is the main component of the biopolymer, is preferably subjected to an agglomeration treatment in a weakly acidic region of less than pH 6 because the carboxyl group of the polysaccharide is easily blocked on the acidic side. Since Al remains in the treated water at a lower temperature, the aggregation treatment at a pH lower than 6 cannot be performed.
On the other hand, in the case of a trivalent iron-based inorganic flocculant, although depending on the quality of the water to be treated, the aggregation is completed even under a low pH condition of about pH 5, and Fe can be prevented from remaining in the treated water.

  However, among the polysaccharides in biologically treated water, there are neutral polysaccharides that do not have carboxyl groups and acidic polysaccharides that contain very little carboxyl groups. Since this type of polysaccharide does not have an ionic bonding force with the positively charged iron hydroxide produced by coordination and bonding of water and hydroxyl groups to the trivalent iron-based inorganic flocculant, it must be agglomerated. I can't. In this case, by using a water-soluble polymer having a phenolic hydroxyl group in combination, good flocculation treatment can be performed, and flocculation treatment water with little RO membrane contamination can be obtained (Patent Documents 1 and 2). ).

  The trivalent iron-based inorganic flocculant has a coagulation action and a flocculation action, and details of each are as follows.

In the agglomeration treatment field, “Coagulation” refers to a phenomenon in which colloidal particles are blocked from their negative charge by addition of electrolyte, the particles become larger and precipitate from a dispersed state.
In the case of a trivalent iron-based inorganic flocculant, iron hydroxide having a large positive charge as a whole formed by coordination and bonding of water and hydroxyl groups to Fe ³⁺ ions has a large coagulation action, and is an RO membrane contaminant. Certain most biopolymers can be insolubilized efficiently. The action of this positively charged iron hydroxide is called “condensation” in technical terms.
The pH at which the coagulation action of the trivalent iron-based inorganic flocculant is exerted greatly is generally pH 3.0 to 4.5, although it depends on the quality of the water to be treated.

On the other hand, “Floculation” refers to a phenomenon in which particles that have increased to some extent are combined to form a lump.
In the case of a trivalent iron-based inorganic flocculant, when it becomes Fe (OH) ₃ in which _three hydroxide ions are bonded to Fe ³⁺ ions, the flocculant has a particle diameter of 1 mm or more and can be clearly confirmed visually (Flock). Form.
Although both “coagulation” and “flocculation” are collectively referred to as “aggregation”, in the present invention, “coagulation action” and “aggregation action: visible agglomerates (floc) as action mechanisms are used. “Form” is distinguished.

In order to solid-liquid-separate the pollutant in the water to be treated with a trivalent iron-based inorganic flocculant and then perform solid-liquid separation with a sedimentation or flotation separator or the like, it is necessary to form a floc.
Since aggregation requires OH ⁻ ion supplementation, the aggregation pH is inevitably higher than the pH of 3.0 to 4.5 having the above-mentioned aggregation action.

As described above, the pH of the water to be treated added so that the trivalent iron-based inorganic flocculant exhibits the “coagulation action” is approximately 4.5 or less. However, in this state, aggregated flocs are not formed, precipitation or flotation efficiency is poor, and even if filtration is performed, iron hydroxide colloid remains in the filtered water, or the filter cloth and filter layer are clogged. To do.
Therefore, it is necessary to neutralize by adding NaOH to an appropriate aggregation pH range to complete the aggregation.
At this time, OH ⁻ ions for completing aggregation are supplied by adding NaOH, but when bicarbonate ions are present in the water to be treated, they are supplied from the bicarbonate ions as shown in the following formula.
HCO ₃ ⁻ → OH ⁻ + CO ₂
Therefore, if the bicarbonate ion concentration of the water to be treated, that is, the alkalinity is high, OH ⁻ is supplied even if the pH is low, the generation pH range of the aggregated floc is, in principle, the lower limit pH of 4.8 where alkalinity exists. Get closer.

In general, the pH range in which the flocs formed by the trivalent iron inorganic flocculant are formed is as wide as pH 5 to 11, but, for example, in water treatment for discharge to public water areas, the drainage standards are met. Neutralization is performed so that the pH is 6 to 8 centering on pH 7, thereby completing the aggregation.
On the other hand, when the agglomerated water is filtered and the filtered water is subjected to RO membrane separation treatment to recover water, from the viewpoint of aggregating action, the pH is within a pH range where the agglomeration is completed. Specifically, the final pH is set in the range of pH 5-7.

Therefore, conventionally, when a trivalent iron-based inorganic flocculant is added to the water to be treated for agglomeration, and the agglomerated water is filtered after being precipitated or floated, the actual agglomeration equipment is trivalent. The tank is composed of three reaction tanks: a tank for adding an iron-based inorganic flocculant, a tank for adding NaOH to form an aggregate floc, and a tank for adding a polymer flocculant to coarsen the floc floc.
However, when water is recovered by performing RO membrane separation treatment of the flocculated / filtered water, if a polymer flocculant is applied, the residue contaminates the RO membrane, so that the polymer flocculant is basically not used. The
Therefore, the pretreatment agglomeration facility in the case of collecting water by RO membrane separation treatment is basically composed of two treatment tanks. The name of each tank differs depending on the facility design and the installer, but in the present specification, the first reaction tank at the front stage is the “inorganic flocculant reaction tank” and the second reaction tank at the rear stage is the “neutralization / coagulation tank”. May be called.

The inorganic flocculant reaction tank is a reaction tank for adding a trivalent iron-based inorganic flocculant and exhibiting a “coagulation action” with iron hydroxide having a positive charge under the condition of pH 3.0 to 4.5. is there.
Here, it is usual that NaOH is added together with the trivalent iron-based inorganic flocculant, and the pH is controlled to be in the above pH range.
Performing primary neutralization with NaOH in advance in the inorganic flocculant reaction tank reduces the amount of NaOH added in the next neutralization / coagulation tank and reduces large fluctuations (hunting) in the pH of the neutralization / coagulation tank. And has the effect of keeping the aggregation pH stable.
Also, depending on the equipment, a sulfuric acid addition line for pH adjustment may be installed in the inorganic flocculant reaction tank.

In the neutralization / coagulation tank, in order to form an appropriate coagulation floc, NaOH is further added to control the pH. As described above, the control target pH is set in the range of pH 5 to 7, which is the aggregation completion pH.
Further, in many cases, a sulfuric acid addition line for pH adjustment is installed in the neutralization / coagulation tank.

  Thus, conventionally, in the agglomeration treatment as a pretreatment in water recovery by RO membrane separation treatment, generally a pH of 3.0 to 4 is obtained by adding a trivalent iron-based inorganic flocculant and NaOH in an inorganic flocculant reaction tank. 1.5, followed by neutralization to pH 5 to 7, which is the final aggregation pH (aggregation completion pH) by further adding NaOH in the neutralization / aggregation tank.

JP 2007-7563 A JP 2011-56496 A

  According to the study of the present inventors, the reaction of the trivalent iron-based inorganic flocculant and the primary neutralization with NaOH are performed in the first reaction tank (inorganic flocculant reaction tank), and the second reaction tank (neutralization / flocculation tank) Further, NaOH is added to perform a neutralization reaction up to the final aggregation pH, that is, the control target pH value of the first reaction tank is made lower than the control target pH value of the second reaction tank, and the final aggregation pH is reached. In the conventional method for stabilizing the water, the quality of the agglomerated water is not stable, and when recovering the RO membrane from this agglomerated water, it is not possible to obtain suitable agglomerated / filtered water as the RO membrane supply water. A problem was found.

The present invention solves this problem, and water to be treated is sequentially passed through a first reaction tank (inorganic flocculant reaction tank) and a second reaction tank (neutralization / coagulation tank) to form a trivalent iron system. It is an object of the present invention to provide a coagulation treatment method and an aggregation treatment apparatus that stably obtain high-quality coagulation treated water while reducing the necessary amount of water treatment coagulant for coagulation treatment with an inorganic coagulant.
Another object of the present invention is to provide a water treatment method and a water treatment device for recovering water by further subjecting the agglomerated water obtained by the agglomeration treatment method and the agglomeration treatment device to solid-liquid separation and RO membrane separation treatment. To do.

As a result of intensive studies to solve the above problems, the inventor of the present invention has set the control target pH value of the first reaction tank lower than the control target pH value of the second reaction tank. Although the final pH in the second reaction tank is stable, the aggregated treated water may be separated by OH ⁻ and remain in the treated water due to the formation of a local high pH region by adding NaOH. It was found that the water quality of the water is unstable. As a result of further investigations based on this knowledge, by setting the control target pH value of the first reaction tank higher than the control target pH value of the second reaction tank, the water quality of the flocculated water is stabilized. It has been found that the water quality can be further improved and the required amount of the water treatment coagulant can be reduced.

  The present invention has been achieved based on such findings, and the gist thereof is as follows.

[1] In a method in which water to be treated is sequentially passed through a first reaction tank to which trivalent iron-based inorganic flocculant and NaOH are added, and a second reaction tank, which are provided in series. The second reaction tank is a tank in which no flocculant is added, no alkali is added, or the flocculant is treated with a very small amount of NaOH, and the trivalent iron-based inorganic flocculant is added to the flocculant. When the lower limit pH value of the pH range in which aggregated flocs are formed in the water to be treated is X, the control target pH value A of the second reaction tank is in the range of X to (X + 0.3) And setting the control target pH value A ′ of the first reaction tank in a range of A to (A + 0.7) to perform the agglomeration treatment.

[2] In [1], the pH value in the first reaction tank is the control target pH value A ′, and the pH value in the second reaction tank is the control target pH value A. An agglomeration method comprising adding NaOH to the first reaction vessel.

[3] In [1], NaOH is added to the first reaction tank so that the pH value in the first reaction tank becomes the control target pH value A ′, and in the second reaction tank An agglomeration method, wherein NaOH is added to the second reaction tank so that the pH value becomes the control target pH value A.

[4] In any one of [1] to [3], before adding the trivalent iron-based inorganic flocculant to the water to be treated, a water-soluble polymer having a phenolic hydroxyl group is added. Aggregating treatment method.

[5] The aggregation treatment method according to any one of [1] to [4], wherein the water to be treated is biologically treated water.

[6] A water treatment method, comprising subjecting the agglomerated water obtained by the agglomeration treatment method according to any one of [1] to [5] to solid-liquid separation and then reverse osmosis membrane separation treatment. .

[7] A first reaction tank and a second reaction tank provided in series, means for sequentially passing water to be treated through the first reaction tank and the second reaction tank, and the first reaction A trivalent iron-based inorganic flocculant addition means and an NaOH addition means provided in the tank, a first pH control means for controlling the pH of the first reaction tank to a control target pH value A ′, and the second A coagulation treatment apparatus having a second pH control means for controlling the pH of the reaction tank to a control target pH value A, wherein the second reaction tank is not added with an alkali without adding a coagulant, or It is a tank that is agglomerated by adding a very small amount of NaOH, and by adding the trivalent iron-based inorganic aggregating agent and aggregating it, the lower limit pH value of the pH range in which agglomerated flocs are formed in the water to be treated is X When the control target pH value A of the second reaction tank is in the range of X to (X + 0.3) Is constant, the control target pH value A of the first reaction vessel 'is, A to coagulation treatment apparatus characterized by being set in a range of (A + 0.7).

[8] In [7], the NaOH addition means of the first reaction tank is controlled by the first pH control means so that the pH value in the first reaction tank becomes the control target pH value A ′. The NaOH addition amount is controlled by the second pH control means so that the NaOH addition amount is controlled and the pH value in the second reaction tank becomes the control target pH value A. Aggregation processing equipment.

[9] In [7], NaOH addition means is provided in the second reaction tank, and the NaOH addition means of the second reaction tank has a pH value in the second reaction tank of the control target pH. The amount of NaOH added is controlled by the second pH control means so as to be a value A, and the NaOH addition means of the first reaction tank has a pH value in the first reaction tank of the control target pH value A. The aggregation treatment apparatus is characterized in that the amount of NaOH added is controlled by the first pH control means so as to be '.

[10] The method according to any one of [7] to [9], wherein means for adding a water-soluble polymer having a phenolic hydroxyl group to the water to be treated is provided upstream of the first reaction tank. A coagulation treatment device.

[11] The aggregation treatment apparatus according to any one of [7] to [10], wherein the water to be treated is biologically treated water.

[12] The aggregation treatment apparatus according to any one of [7] to [11], the solid-liquid separation means for solid-liquid separation of the aggregation treated water obtained by the aggregation treatment apparatus, and the solid-liquid separation means A water treatment device comprising: a reverse osmosis membrane separation device for subjecting the obtained separated water to a reverse osmosis membrane separation treatment.

ADVANTAGE OF THE INVENTION According to this invention, in the coagulation process using a trivalent iron type inorganic coagulant | flocculant, while reducing the required amount of a water treatment coagulation chemical | medical agent, the high quality coagulation process water can be obtained stably.
The agglomerated treated water obtained by the present invention has good water quality, excellent water quality stability, and low RO membrane contamination, so that it is subjected to RO membrane separation treatment by solid-liquid separation. It is possible to recover water stably and efficiently over a long period of time.

It is a systematic diagram which shows an example of embodiment of the water treatment apparatus of this invention. 4 is a graph showing the relationship between the amount of NaOH added and the pH value in Experimental Example 1. In Experiment 2, a graph showing the relationship between the quality of the aggregation pH and aggregation and filtered water in the case of flocculation treatment with FeCl ₃ and a phenolic resin, (a) drawing SFF and MFF aggregation-filtered water (B) The figure shows the same UV260 and netNTU. In Experimental Example 2, it is a graph showing the relationship between the aggregation pH and the water quality of the coagulation / filtered water when coagulation treatment is performed using only FeCl ₃ , (a) the figure shows the SFF and MFF of the coagulation / filtered water, (B) The figure shows the same UV260 and netNTU. It is a graph which shows the relationship between pH in Experimental example 3, and the leak rate of a phenol-type resin.

  Hereinafter, embodiments of the present invention will be described in detail.

[Aggregating treatment method and aggregating treatment apparatus]
In the flocculation treatment method of the present invention, water to be treated is sequentially passed through a first reaction tank and a second reaction tank to which trivalent iron-based inorganic flocculant and NaOH are added in series. In the flocculation method, when the lower limit pH value of the pH range in which flocculation flocs are formed in the water to be treated by adding the trivalent iron-based inorganic flocculant and performing the flocculation treatment is X, the second The control target pH value A of the reaction tank is set in the range of X to (X + 0.3), and the control target pH value A ′ of the first reaction tank is set in the range of A to (A + 0.7). And aggregating treatment is performed.

  The coagulation treatment apparatus of the present invention comprises a first reaction tank and a second reaction tank provided in series, means for sequentially passing the water to be treated through the first reaction tank and the second reaction tank, A trivalent iron-based inorganic flocculant addition means and an NaOH addition means provided in the first reaction tank; a first pH control means for controlling the pH of the first reaction tank to a control target pH value A ′; A coagulation treatment apparatus having a second pH control means for controlling the pH of the second reaction tank to a control target pH value A, and adding the trivalent iron-based inorganic coagulant to perform the coagulation treatment. The control target pH value A of the second reaction tank is set in the range of X to (X + 0.3), where X is the lower limit pH value of the pH range in which aggregated flocs are formed in the water to be treated. The control target pH value A ′ of the first reaction tank is set within the range of A to (A + 0.7) And features.

<Action mechanism>
The present inventor performs coagulation with a trivalent iron-based inorganic coagulant and primary neutralization with NaOH in the first reaction tank (inorganic flocculant reaction tank), and finally in the second reaction tank (neutralization / coagulation tank). In the conventional method for neutralizing to the flocculation pH, that is, the control target pH value of the first reaction tank is lower than the control target pH value of the second reaction tank to stabilize the final flocculation pH. The following knowledge was obtained about the reason why the water quality is not stable.

In the conventional method, the pollutant of the water to be treated by the trivalent iron-based inorganic flocculant is “condensed” in the inorganic flocculant reaction tank. Here, in order to accelerate the coagulation action, primary neutralization is performed by adding NaOH in order to reduce the amount of NaOH added in the neutralization / coagulation tank and suppress a large fluctuation in the control pH.
Next, NaOH is added in a neutralization / coagulation tank so that the coagulation pH can be stably formed.
However, in the conventional method, in the neutralization / coagulation tank, as shown in an experimental example described later, a region having a high pH is formed locally by NaOH added to the neutralization / coagulation tank. In other words, condensation by free OH ⁻ or re-elution and re-dispersion of agglomerated contaminants occur.
Moreover, while the inorganic flocculant reaction tank is rapid stirring, the neutralization / flocculation tank is generally slow stirring for the purpose of forming agglomerated flocs. On the other hand, lowering the diffusion rate of OH ⁻ increases the occurrence of local high pH and increases its duration. In fact, this locally high pH is expected to reach pH 10.
The re-eluted and re-dispersed contaminants are not collected by re-coagulation because the coagulation action of the trivalent iron-based inorganic coagulant has already been reduced.

Even when a water-soluble polymer having a phenolic hydroxyl group is used together with a trivalent iron-based inorganic flocculant, a reaction product of contaminants such as biopolymers and the water-soluble polymer incorporated in the iron hydroxide floc Is peeled off by OH ⁻ which brings about a high local pH, and is dispersed or dissolved in the liquid side in a colloidal state and partly in a dissolved state. Thereafter, the local high pH is finally eliminated in the neutralization / coagulation tank, and even if the pH falls below 6.5, the iron coagulation force has already been lost, so the colloidal material is recoagulated. The quality of the flocculated water is worse than when only the trivalent iron-based inorganic flocculant is used.

  As described above, in the conventional method, generation of locally high pH in the tank by addition of NaOH in the neutralization / coagulation tank, re-elution of coagulated or coagulated contaminants, and deterioration of water quality due to re-dispersion are avoided. However, the current situation is that this deterioration of water quality has not been recognized.

On the other hand, in the present invention, coagulation and coagulation are completed at once in the inorganic coagulant reaction tank, and NaOH is not added in the neutralization / coagulation tank, or even when added, it is locally added by adding NaOH as a small amount. The control target pH value of the neutralization / flocculation tank is set lower than the control target pH value of the inorganic flocculant reaction tank so as to suppress the generation of high pH.
In this way, the control target pH value of the inorganic flocculant reaction tank is set lower than the control target pH value of the neutralization / coagulation tank, and operation is performed so that no substantial NaOH is added to the neutralization / coagulation tank. In order to obtain a water quality equal to or higher than that of the contaminated treated water by preventing it from leaving and remaining in the treated water due to OH ⁻ in the neutralization / coagulation tank. This makes it possible to reduce the amount of water treatment coagulant required.

  In the present invention, the control target pH value of the neutralization / coagulation tank is set to the nearest value above the lower limit of the appropriate coagulation pH range as follows. Even when the pH falls below the pH range, the pH can be returned to the neutralization / coagulation tank to obtain a stable coagulation effect.

  In the present invention, the neutralization / coagulation tank of the second reaction tank is not added with a coagulant such as a trivalent iron-based inorganic coagulant, and is added with no alkali such as NaOH or with a very small amount of NaOH. A tank to be agglomerated.

<Setting method of control target pH value>
In the present invention, a pH range in which aggregated flocs are formed in the water to be treated by adding a trivalent iron-based inorganic flocculant (hereinafter, this pH range may be referred to as “appropriate aggregate pH range”). Control of the second reaction tank (neutralization / coagulation tank) where X is the lower limit pH value (hereinafter, this lower limit pH value may be simply referred to as “lower limit pH value X”). The target pH value A is set in the range of X to (X + 0.3), and the control target pH value A ′ of the first reaction tank (inorganic flocculant reaction tank) is set in the range of A to (A + 0.7). Set to, and perform aggregation processing.

  The proper flocculation pH range and the lower limit pH value X vary depending on the water quality of the water to be treated, for example, the alkalinity, and cannot be generally defined. For this reason, it is preferable to determine the proper coagulation pH range and the lower limit pH value X by conducting an experiment for each water to be treated.

Specifically, the determination of the lower limit pH value X is carried out by adding a sufficiently diluted NaOH aqueous solution to the sample water in a predetermined amount in a plurality of times by the method shown in Experimental Example 1 described later. This can be done by recording the pH at which was formed. In this case, since it may take time to form flocs, after adding the NaOH aqueous solution once, rapid stirring is performed for at least 2 minutes, and the pH is measured here. Next, it is necessary to carry out slow stirring (50 rpm in Experimental Example 1) for 1 minute or more to confirm floc formation.
Since microbial flocs and the like already exist in the water to be treated and it may be difficult to distinguish them from the flocs formed by the trivalent iron-based inorganic flocculant, it is preferable to simultaneously compare with the blank sample.
In addition, even if flocs are formed, if the liquid is colored yellow by iron, it is considered that the formation of aggregated flocs is not completed.
If the determination of completion of aggregation is not possible, including yellow coloring on the liquid side, No. Filter with 2 sheets of 5A filter paper, check whether 500 mL can be filtered smoothly, and judge especially by the yellowishness of the remaining liquid on the filter paper in the latter half of the filtration. In the case of incomplete aggregation, the filtration cannot be performed smoothly, and a yellowish color is observed in the remaining liquid.
In addition, if it is an operator familiar with implementation operation, the lower limit pH value X for completing aggregation can be grasped | ascertained as an experience value.

  On the other hand, the upper limit pH value of the proper flocculation pH range can be confirmed by the method shown in Experimental Example 2 below, and the proper flocculation pH range can be determined from these results.

  From the experimental examples 1 and 2 described later, the results of examining the proper aggregation pH range of biologically treated water in various liquid crystal factories are as described below, and the upper limit pH value of the appropriate aggregation pH range is relative to the lower limit pH value X. In the range of +0.8 to 1.0. Therefore, it can be determined that good treated water quality can be obtained by setting the range of the lower limit pH value X + 0.7 to the proper flocculation pH range and adjusting the final flocculation pH within this range.

As described above, the control target pH values of the inorganic flocculant reaction tank and the neutralization / flocculation tank in the present invention are set as follows with respect to the previously obtained lower limit pH value X.
First, the control target pH value A of the neutralization / coagulation tank is set in the range of X to (X + 0.3) closest to the lower limit pH value X.
Next, the control target pH value A ′ of the inorganic flocculant reaction tank is set in the range of A to (A + 0.7).
With the above settings, it is substantially unnecessary to add NaOH in the neutralization / coagulation tank, and generation of local high pH due to the addition of NaOH and cohesive failure caused thereby can be prevented.
Setting the pH control value to the above control target pH value A in the neutralization / coagulation tank is to minimize NaOH in a situation where the pH of the inflow water from the inorganic coagulant reaction tank is below the lower limit pH value X for some reason. This is for the purpose of adding a limited amount to avoid a situation in which aggregated floc is not formed. The control target pH value A of the neutralization / coagulation tank may be not less than the lower limit pH value X, but is preferably in the range of (X + 0.1) to (X + 0.2) in consideration of the effect of actual pH fluctuation. Is set.

  On the other hand, in the inorganic flocculant reaction tank, the control target pH value A ′ is within the range of A to (A + 0.7) with respect to the control target pH value A of the neutralization / coagulation tank in order to complete the coagulation and aggregation as much as possible. Set with. The upper limit of the control target pH value A ′ is (A + 0.7), as described above, generally, the range of the proper aggregation pH range is +0.8 to 1.0, and the aggregation lower limit pH value X + 1. If it is in the range of 0.0, it is due to being within the proper coagulation pH range. The control target pH value A ′ of the inorganic flocculant reaction tank is preferably set to a value slightly higher than the lower limit pH value X. Therefore, the control target pH value A ′ is preferably A to (A + 0.5) or more. Preferably, it is in the range of (A + 0.1) to (A + 0.3).

  In the present invention, the control target pH value A ′ of the inorganic flocculant reaction tank and the control target pH value A of the neutralization / coagulation tank may be the same. Even in this case, defective aggregation can be prevented by providing an inorganic flocculant reaction tank and a neutralization / coagulation tank and controlling the pH in the neutralization / coagulation tank to the lower limit pH value X or more.

  In the present invention, by setting the control target pH value A ′ of the inorganic flocculant reaction tank and the control target pH value A of the neutralization / coagulation tank in this way, the neutralization / coagulation tank does not add NaOH. Processing is also possible. That is, by adding NaOH in the inorganic flocculant reaction tank, it is possible to adjust the pH so that both the control target pH value A ′ of the inorganic flocculant reaction tank and the control target pH value A of the neutralization / flocculation tank are achieved. It becomes. However, in the present invention, NaOH may be added to the control target pH value A by adding NaOH also in the neutralization / coagulation tank. Even in that case, the pH adjustment is basically performed by adding NaOH in the inorganic flocculant reaction tank, and the addition of NaOH in the neutralization / flocculation tank is performed only when the pH falls below the control target pH value A. .

<Trivalent iron-based inorganic flocculant>
As the trivalent iron-based inorganic flocculant used in the present invention, those used for general flocculation treatment can be used, and ferric chloride (FeCl ₃ ), ferric sulfate (Fe ₂ (SO ₄ ) ₃ ). Polyferric sulfate ([Fe ₂ (OH) _n (SO ₄ ) _{3 -n / 2} ] _m ) and the like can be used. These trivalent iron-based inorganic flocculants may be used alone or in combination of two or more.
The amount of the trivalent iron-based inorganic flocculant added varies depending on the quality of the water to be treated (the amount of the agglomeration target) and whether or not a water-soluble polymer having a phenolic hydroxyl group is used, but usually in terms of Fe ³⁺ By using the additive at a rate of about 5 to 30 mg / L with respect to the water to be treated, good agglomerated treated water can be obtained.

<Water-soluble polymer having phenolic hydroxyl group>
When water to be treated contains neutral polysaccharides that cannot be agglomerated with trivalent iron-based inorganic flocculants or biopolymers that are difficult to agglomerate with trivalent iron-based inorganic flocculants, Prior to adding the trivalent iron-based inorganic flocculant, it is preferable to add a water-soluble polymer having a phenolic hydroxyl group.

Examples of the water-soluble polymer having a phenolic hydroxyl group used in this case include the following vinylphenol polymers (1) to (3).
(1) Vinylphenol homopolymer
(2) Modified vinylphenol homopolymer
(3) Copolymer of vinylphenol and / or modified vinylphenol and hydrophobic vinyl monomer

  Examples of the modified vinylphenol of (2) above include vinylphenols in which the phenyl group is chemically modified with some compound, such as vinylphenol substituted with an alkyl group or allyl group, and halogenated vinylphenol.

  Examples of the hydrophobic vinyl monomer (3) include water-insoluble or poorly water-soluble vinyl monomers such as ethylene, acrylonitrile, and methyl methacrylate. The ratio of vinyl phenol and / or modified vinyl phenol in the copolymer of such a hydrophobic vinyl monomer and vinyl phenol and / or modified vinyl phenol is 0.5 or more, particularly 0.7 or more in molar ratio. Preferably there is. When this ratio is less than 0.5, it is not preferable because it is hardly soluble or insoluble in an aqueous alkali solution described later.

The vinylphenol polymers (1) to (3) preferably have a weight average molecular weight of 5,000 or more, for example, 5,000 to 100,000, and the polymer having such a molecular weight is usually provided as a powder.
In the present invention, the weight average molecular weight is a value measured by a GPC method (gel permeation chromatography method) and calculated using a standard polystyrene calibration curve.

  The vinylphenol polymers (1) to (3) are insoluble or hardly soluble in water, but are soluble in an alkaline aqueous solution. Therefore, these vinylphenol polymers are preferably used in a liquid form as an alkaline aqueous solution.

  In this case, examples of the alkaline substance in the alkaline aqueous solution include hydroxides such as various alkali metals or alkaline earth metals, ammonia, and amines, but caustic soda (NaOH) or caustic potash is easy to obtain and handle. (KOH) is preferred.

For the preparation of the alkaline aqueous solution of the vinylphenol polymer, for example, the vinylphenol polymer powder is suspended in water, and an alkaline substance is added thereto to obtain a brown to black brown aqueous solution. Therefore, the addition amount of the alkaline substance may be an amount that dissolves the vinylphenol polymer powder, and is generally added so as to become an alkaline aqueous solution of 10 to 30% by weight.
The concentration of the vinylphenol polymer in the alkaline aqueous solution is arbitrary, but generally it is preferably about 5 to 20 (w / v)%.

  As the water-soluble polymer having a phenolic hydroxyl group used in the present invention, for example, a novolac-type phenol resin is obtained by reacting phenols and aldehydes in the presence of an acid catalyst, and the alkali of the novolac-type phenol resin is used. A phenol resin with a low low molecular weight component obtained by adding an aldehyde to the solution and performing a resol type secondary reaction in the presence of an alkali catalyst (hereinafter sometimes referred to as “secondary reaction phenol resin”). An alkaline solution is also preferable.

That is, a novolak-type phenol resin is used as an alkaline solution, 0.2 to 0.4 mol of formaldehyde is added per mol of the phenol ring, and the reaction is performed at 80 to 100 ° C. for 1 to 12 hours. In this reaction, formaldehydes are added to the phenol ring of the low molecular weight component containing the phenol dinuclear body to generate a methylol group of the reactive group, which reacts with the existing phenol condensate, so that the low molecular weight component is Converts to high molecular weight agglomerated active ingredient.
At the same time, addition of formaldehyde, methylol group generation, addition reaction to other condensation polymer components occurs in the phenol ring of the existing condensation polymer component, and the average molecular weight of the entire resin is from 2000 to 6000 of the original resin, It increases to 5,000 to 30,000, several times.

In this reaction, the phenol ring changes from a secondary structure (linear) connected by two hands to a tertiary structure connected by three hands, which reduces the degree of freedom of the polymer chain, resulting in an increase in melting point. To do.
When the melting point rise is small, the reduction of the low molecular weight component is insufficient. On the other hand, if the melting point increases too much, and further the melting point is not measured (decomposition starts at 230 ° C. or higher and it is not possible to know whether the melting point is present), the molecular weight of the phenol resin becomes 1 million orders or more. It cannot be dissolved and precipitates and solidifies. Further, even if the liquid is kept, the viscosity increases, solidification starts over time, and it cannot be put to practical use as a flocculant.

  The novolak-type phenol resin used as the raw material for the above-mentioned resol-type secondary reaction is obtained by subjecting phenols and aldehydes to polycondensation reaction in the presence of an acidic catalyst in a reaction vessel according to a conventional method, and then under normal pressure and reduced pressure. Thus, dehydration and removal of unreacted phenol are performed.

Examples of the phenols used for the production of the novolak-type phenol resin include phenols, alkylphenols such as o, m and p cresols, o, m and p ethylphenols and xylenol isomers, α and β Examples include polyaromatic phenols such as naphthol, polyphenols such as bisphenol A, bisphenol F, bisphenol S, pyrogallol, resorcin, and catechol, and hydroquinone, but are not limited thereto. These phenols may be used individually by 1 type, and may mix and use 2 or more types.
Of these, practical substances are phenol, cresols, xylenols, and catechol.

On the other hand, examples of aldehydes include formaldehyde, paraformaldehyde, acetaldehyde, propylaldehyde, benzaldehyde, salicylaldehyde, glyoxal, and the like, but are not limited thereto. These aldehydes may be used individually by 1 type, and may mix and use 2 or more types.
Among these, practical substances are formaldehyde and paraformaldehyde.

The melting point of the novolak type phenol resin used as the raw material for the resol type secondary reaction is 65 to 120 ° C., and the weight average molecular weight is preferably 1000 to 6000, and particularly preferably 2000 to 6000.
Moreover, the pH of the alkali solution of the novolak type phenol resin is about pH 11 to 13, and the concentration of the novolak type phenol resin in the alkali solution of the novolak type phenol resin is about 5 to 50% by weight, particularly about 10 to 30% by weight. Preferably there is.

  As the aldehydes added to the novolac phenol resin alkaline solution for the resol type secondary reaction, the same aldehydes as the above-mentioned novolac phenol resin raw material may be used alone or in combination of two or more. These can be used in combination, and among these, formaldehyde and paraformaldehyde are practical, but are not limited thereto.

  The amount of aldehyde added to the alkali solution of the novolak type phenol resin is 0.2 to 0.4 mol per mol of the phenol ring in the novolak type phenol resin. A preliminary test for confirming the relationship with the melting point of the secondary reaction phenol resin is performed, and it is preferable to determine the amount of addition based on the result so that a secondary reaction phenol resin having a desired melting point can be obtained.

The melting point of the secondary reaction phenol resin obtained by performing the resol type secondary reaction is preferably 130 to 220 ° C, more preferably 150 to 200 ° C.
The weight average molecular weight of the secondary reaction phenol resin is preferably 5000 or more, and more preferably 10,000 or more. On the other hand, when the weight average molecular weight exceeds 50,000, some of the molecules having a molecular weight of 1 million or more are formed, the viscosity is high, and there is a high possibility of further crosslinking and generation of insoluble matter over time. The weight average molecular weight of the resin is preferably 50000 or less, particularly 30000 or less.
Further, the weight average molecular weight of the secondary reaction phenol resin is preferably about 2 to 5 times the weight average molecular weight of the novolac type phenol resin before the reaction, that is, the raw material of the resol type secondary reaction.

  The secondary reaction phenolic resin has a phenolic dinuclear content of less than 3% by weight, particularly preferably 2% by weight or less, and a content of a low molecular weight component having a molecular weight of 624 or less is 10% by weight or less. It is preferable that More preferably, the content of the low molecular weight component having a molecular weight of 624 or less is 5% by weight or less. Further, the content of the low molecular weight component having a molecular weight exceeding 624 and not more than 1200 is preferably 10% by weight or less, particularly preferably 7% by weight or less.

In addition, the secondary reaction phenolic resin generally has a low molecular weight component having a molecular weight of 1000 or less and a binuclear content of generally 15% by weight or less, preferably 10% or less, with respect to the novolak type phenol resin that is a raw material for the resol type secondary reaction. When used for agglomeration, the agglomerated water that is preferred as the feed water for the membrane separation process, in which the amount of unagglomerated material remaining on the agglomerated water side is remarkably reduced and TOC and COD _Mn are remarkably reduced. can get.

  In the present invention, the above-mentioned secondary reaction phenol resin, the above-mentioned vinylphenol polymers (1) to (3) and the like (hereinafter sometimes collectively referred to as “phenol resins”) are alkaline solutions. The pH of the water to be treated when added as is preferably neutral or alkaline, particularly preferably 6 or more, for example, 6 to 9. If this pH is less than 6, the phenolic resin will precipitate during the addition, and the agglomeration performance will deteriorate. Accordingly, when the pH of the water to be treated is less than 7, the pH is adjusted by adding an alkali as necessary.

  If the amount of phenolic resin added is too small, the coagulation effect due to the addition of phenolic resin cannot be obtained sufficiently, and if it is too much, the effect will not change, but it is not economical. Usually, it is preferably 0.20 to 5.0 mg / L in terms of the amount of active ingredient relative to the water to be treated.

<Influence of acid addition>
In an actual agglomeration reaction facility, an acid addition facility such as sulfuric acid or hydrochloric acid may be provided together with an NaOH addition facility for pH adjustment.
In the present invention, in order to reduce the consumption of the inorganic flocculant due to the alkalinity of the water to be treated of the trivalent iron-based inorganic flocculant, when reducing the alkalinity with an acid in advance, the water after acid addition is treated as the water to be treated. Define. That is, the water to be treated that is subject to agglomeration treatment in the present invention may have been previously added with an acid. Here, “preliminarily” is the addition of acid in the agglomeration reaction facility, specifically, the pipe of the water to be treated leading to the inorganic flocculant reaction tank, the tank for the water to be treated, the biological treatment tank in the previous stage, and the like. .

Adding acid along with trivalent iron-based inorganic flocculant and NaOH in an inorganic flocculant reaction tank or neutralization / flocculation tank, especially adding NaOH and acid to the same tank wastes NaOH and acid. In the present invention, as a general rule, no acid is added and the treatment water is temporarily changed due to fluctuations in the quality of the treated water. When it is necessary to lower the pH, it is preferable to increase the amount of the trivalent iron-based inorganic flocculant added.
In addition, in order to set the control target pH value A of the neutralization / flocculation tank to be lower than the control target pH value A ′ of the preceding inorganic flocculant reaction tank, acid is not added to the neutralization / coagulation tank, It is preferable to adjust the pH by adding NaOH only when the pH is lower than the lower limit pH value X.

[Water treatment method and apparatus]
The water treatment method of the present invention is characterized in that the agglomerated water obtained by the above-described agglomeration method of the present invention is subjected to RO membrane separation treatment after solid-liquid separation.
The water treatment apparatus of the present invention is obtained by the above-described flocculation apparatus of the present invention, the solid-liquid separation means for solid-liquid separation of the flocculated water obtained by the flocculation apparatus, and the solid-liquid separation means. And an RO membrane separation device for subjecting the separated water to RO membrane separation treatment.

<Evaluation of RO membrane water supply>
First, water quality suitable as RO membrane supply water will be described.

The present inventor analyzed and evaluated the suitability of the water quality as RO membrane supply water by the following SFF, MFF, SDI, and netNTU, and set the evaluation categories shown in Table 1 below.
SFF is an indicator of biopolymer contamination, and MFF, SDI, and netNTU are indicators of particulate matter (silt, metal hydroxide colloid, colloidal material with insufficient aggregation) contamination.

(SFF)
SFF (Soluble Polymer Fouling Factor) is a water quality evaluation method that evaluates the presence of biopolymers containing neutral polysaccharides and the degree of influence of membrane contamination, as disclosed in JP2012-213676A.
SFF performs suction filtration of 500 mL of RO membrane permeate or distilled water with virtually no RO membrane contaminants and sample water at 500 mHg using MF (microfilter) with a maximum pore size of 0.45 μm and 47 mmφ, respectively. The respective filtration times T ₀ and T ₁ are measured, and the water temperature is corrected and determined by the ratio of T ₁ / T ₀ .

(MFF)
The MFF (fouling factor) is determined by the ratio of T ₂ / T _{1 after} the above SFF measurement, by further filtering 500 mL of sample water and measuring the filtration time T ₂ .
MFF determines the suitability of RO membrane supply water. The following SDI (silt density index) defined in ASTM D4189, FI (fouling index) defined in JIS K3802 (SDI and FI are the same) In this method, the contamination with fine turbidity is determined.

(SDI)
SDI (Silt Density Index) is a 15-minute pressure filtration at 30 psi using sample water with MF (microfilter) with a maximum pore size of 0.45 μm and 47 mmφ. Although it is a value (ASTM D4189) indicating how much the amount of water decreased per minute, SDI was estimated by a regression equation in the determination of the following evaluation categories from the simultaneous measurement values of MFF and SDI.

<NetNTU>
netNTU is a numerical value obtained by subtracting the blank value of ultrapure water (or distilled water) from the NTU value measured with a portable turbidimeter “2100P” manufactured by HACH, and determining the minute turbidity up to the second digit of the decimal point.

  The agglomerated water obtained by the agglomeration treatment method and the agglomeration treatment apparatus of the present invention can be filtered to obtain filtered water having water quality suitable as the RO membrane supply water.

<Water treatment>
Below, with reference to FIG. 1 which shows an example of embodiment of the water treatment apparatus of this invention, the water treatment method and water treatment apparatus of this invention are demonstrated.

  In FIG. 1, 1 is a first reaction tank (inorganic flocculant reaction tank), which has a stirrer and a pH meter 11, and a trivalent iron-based inorganic flocculant addition means (trivalent iron-based inorganic flocculant addition line). ) And NaOH addition means (NaOH addition line). 2 is a second reaction tank (neutralization / coagulation tank), which has a stirrer and a pH meter 12 and is provided with NaOH addition means (NaOH addition line). A means for adding NaOH is not necessarily required. The neutralization / flocculation tank 2 is not provided with a trivalent iron-based inorganic flocculant addition means.

The inorganic flocculant reaction tank 1, the neutralization / flocculation tank 2, and the controller 10 constitute an aggregating apparatus of the present invention.
The controller 10 serves as both the first pH control means and the second pH control means in the coagulation treatment apparatus of the present invention, and performs the following pH control (1) or (2).
(1) based on the respective pH value input from the pH meter 12 of the inorganic coagulant pH of the reaction vessel 1 meter 11 and neutralization and flocculation tank 2, to control the operation of the chemical feed pump P ₂ of NaOH addition means Then, the pH of the reaction liquid in the inorganic flocculant reaction tank 1 is adjusted to the control target pH value A ′, and the pH of the reaction liquid in the neutralization / coagulation tank 2 is adjusted to the control target pH value A. In this case, the addition of NaOH to neutralization and flocculation tank 2 is not required, it is possible to omit the chemical feed pump P ₃ and dosing line.
(2) on the basis of the pH value input from the pH meter 11 of the inorganic coagulant reaction tank 1, and controls the operation of the chemical feed pump P ₂ of NaOH addition means, the inorganic coagulant reaction solution in the reaction tank 1 The pH is adjusted to the control target pH value A ′, and the chemical injection pump P ₃ of the NaOH addition means is controlled as necessary based on the pH value input from the pH meter 12 of the neutralization / flocculation tank 2. Then, the pH of the reaction solution in the neutralization / coagulation tank 2 is adjusted to the control target pH value A.
The measured value of the pH meter 11 of the inorganic flocculant reaction tank 1 is higher than the control target pH value A ′ due to some upstream condition fluctuations such as fluctuations in the quality of the water to be treated and fluctuations in the amount of water. If, by increasing the discharge amount of chemical feed pump P ₁ of trivalent iron-based inorganic flocculant principle manually, pH control to lower the pH it is performed. Conversely, if the discharge amount of chemical feed pump P ₂ of NaOH added means becomes significantly more, weight loss the discharge amount of the chemical feed pump P ₁ of trivalent iron-based inorganic flocculant principle manually.

  In addition, prior to the addition of the trivalent iron-based inorganic flocculant, when the agglomeration treatment with the above-described phenolic resin is performed, an agglomeration treatment tank in which the phenolic resin is added to the preceding stage of the inorganic flocculant reaction tank 1 to perform the agglomeration treatment. (It may also serve as a storage tank for water to be treated).

  The agglomerated water that has been successively passed through the inorganic flocculant reaction tank 1 and the neutralization / agglomeration tank 2 and agglomerated at a predetermined pH with the trivalent iron-based inorganic aggregating agent is fed to the flotation separator 3. Floated and separated, the separated water is further filtered by the filtration device 4, the filtered water is RO membrane separated by the RO membrane separation device 5, and RO permeated water is recovered as treated water.

  In such a water treatment apparatus, according to the agglomeration treatment apparatus of the present invention, as described above, it is possible to obtain the agglomerated / filtered water having low membrane contamination suitable as the RO supply water. The water can be recovered stably and efficiently over a long period of time.

FIG. 1 shows an example of an embodiment of the water treatment apparatus of the present invention, and the water treatment apparatus of the present invention is not limited to that of FIG.
For example, the solid-liquid separation means is not limited to a flotation separation device, and may be a sedimentation tank, and the NaOH addition pump may be an addition of circulating NaOH dilution by opening / closing an electric valve. That is, the NaOH dilution liquid is circulated by the chemical injection pumps P ₂ and P ₃ for adding NaOH, and the opening and closing and opening time of the electric valve provided in the chemical injection line to the reaction tank is determined according to the pH of each reaction tank. It is also possible to control the addition of NaOH by adjustment or manual valve opening adjustment.

  Experimental examples, examples and comparative examples are given below.

Hereinafter, as the trivalent iron-based inorganic flocculant, ferric chloride liquid product (38 wt% FeCl ₃ aqueous solution = Fe equivalent concentration 13.1 wt% aqueous solution) (hereinafter simply referred to as “FeCl ₃ ”). ) Or polyferric sulfate liquid product ([Fe ₂ (OH) _n (SO ₄ ) _{3−n / 2} ] _m aqueous solution (hereinafter referred to simply as “polyferric sulfate”) having an Fe equivalent concentration of 11% by weight. In addition, “Kuribata BP201” (hereinafter referred to as “BP201”) manufactured by Kurita Kogyo Co., Ltd. was used as the secondary reaction phenol resin alkali solution.
The addition amount of the trivalent iron-based inorganic flocculant and BP201 indicates the addition amount as a product, and the addition amount as a pure component is calculated from the addition amount and the content ratio of the active ingredient. Value.
Further, for the pH adjustment, 1 wt% NaOH aqueous solution was used in Experimental Example 1, and 48 wt% NaOH aqueous solution was used in the other experimental examples.

  No. Unless otherwise specified, filtration with 5A filter paper is No. The filtration was performed with two sheets of 5A filter paper, and this filtration corresponds to filtration by a gravity type two-layer filtration device (capturing a suspension having a particle diameter of 1 μm or more).

[Experimental Example 1: Confirmation of preferred aggregation pH value from appearance observation]
The wastewater of the liquid crystal A factory is biologically treated, and FeCl ₃ is added to the biologically treated water for agglomeration treatment. The agglomerated treated water is subjected to pressure levitation treatment, followed by gravity-type two-layer filtration, and the filtered water is subjected to RO membrane separation treatment. From the process of obtaining recovered water, biologically treated water was collected, and laboratory tests were conducted to investigate the preferred aggregation pH value from the observation of the appearance of aggregate flocs when pH was adjusted by adding NaOH after adding FeCl _3. went.
The experimental conditions are as follows.
500 mL of sample water (biologically treated water) was collected in a jar tester manufactured by Miyamoto Seisakusho, and FeCl ₃ was added at ₃₀ , 45, 60, or 100 mg / L with stirring at 150 rpm, and then 0.1 mL of 1 wt% NaOH aqueous solution ( 2 mg / L) multiple times, and after each addition of NaOH, rapidly stir at 150 rpm so that a local high pH region does not occur for about 2 to 4 minutes after the addition, and record the pH value when the pH is stable Thereafter, the presence or absence of aggregated floc formation was confirmed by slow stirring at 50 rpm.
In addition, the alkalinity of the biological treatment water which is sample water is 20 mg / L, and an alkalinity is lower than a domestic tap water level (30-60 mg / L).

FIG. 2 shows the relationship between the NaOH addition amount and the pH value at each FeCl ₃ addition amount in this experiment.
Further, the pH value at which agglomeration floc can be confirmed visually was examined, and is shown by a broken line in FIG. In Figure 2, solid lines, the free OH ^- indicating the value of the generated pH 7 ^- ion (free OH).
This experiment confirmed the following.

(1) As is clear from FIG. 2, the pH value at which the formation of aggregated flocs was visually confirmed was pH 5.7 in any of the FeCl ₃ addition amounts 30, 45, 60, and 100 mg / L. It was.
In general, aggregation flocs are not formed at pH 5 to 5.5, which is considered to be aggregation floc formation pH, because the concentration of bicarbonate ions (alkalinity) having pH buffering property of sample water is low, and OH ⁻ necessary for aggregation This is because much of it must be supplied with NaOH.
(2) In any amount of FeCl ₃ added, OH ⁻ begins to be excessive without being adsorbed on the iron hydroxide, and after reaching pH 7 or higher, the pH rises rapidly. Thus, free OH ⁻ If there is, it is presumed that a part of the condensed and agglomerated contaminants is once again dissolved.
(3) According to the visual judgment only of the state of formation of the aggregated floc, the size of the aggregated floc is secured even when the pH exceeds 7.0, but when the pH exceeds 8.0, the floc becomes small and exceeds pH 9.0. Furthermore, the flocs became smaller and coloring was observed on the liquid side.
That is, in visual appearance observation, it can be said that a good aggregation pH is 5.7 to 8.0.
However, from the viewpoint of the water quality as the RO membrane supply water, the appropriate coagulation pH range is pH 5.7 to 6.5 as the result of the following Experimental Example 2. The proper aggregation pH range can be determined to be 5.7 to 6.5, and the lower limit pH value X can be determined to be 5.7.

[Experimental Example 2: Relationship between aggregation pH and aggregation / filtered water quality]
Using the same sample water (biologically treated water) as in Experimental Example 1, 2 mg / L of BP201 was added and allowed to react sufficiently, then 60 mg / L of FeCl ₃ was added, and a predetermined pH was reached after 3 to 5 seconds. After adding a theoretical amount of NaOH for adjustment to 6 minutes and rapidly stirring at 150 rpm for 6 minutes, the mixture was gently stirred at 50 rpm for 6 minutes to form aggregated flocs. The agglomerated water is No. Filtration with 5A filter paper gave filtered water.

  About this filtered water, while measuring SFF, MFF, and netNTU by the above-mentioned method, UV260 is measured as a presence indicator of a soluble organic substance by the following method, and the relationship with the aggregation pH value is shown in FIG. )Pointing out toungue.

<UV260>
About the sample water, the light absorbency value of a wavelength 260nm and 50mm cell was measured with the spectrophotometer.

Moreover, except that BP201 was not added and the aggregation treatment was performed only with FeCl ₃ , the aggregation, filtration and filtered water were evaluated in the same manner as described above, and the results are shown in FIGS. 4 (a) and 4 (b).

The following can be understood from the evaluation classification of the suitability of the water quality of the RO membrane feed water in Table 1 and the results shown in FIGS.
From FIG. 3A showing the relationship between the aggregation pH and SFF and MFF, the proper aggregation pH range in which the optimum result is obtained is determined to be 5.7 to 6.5.
When the pH is 6.5 or more, the biopolymer presence index SFF increases with an increase in pH, and the fine particle presence index MFF increases remarkably.
An increase in SFF is interpreted as a re-elution of the biopolymer once captured by NaOH.
Further, the large increase in MFF is interpreted as a part of the aggregated floc containing the biopolymer is separated together with iron hydroxide by NaOH and dispersed in a colloidal form.
The increase in colloidal material corresponds to the increase in netNTU, which is an indicator of microturbidity in FIG.
The increase in UV 260 is considered to be the result of the addition of an increase in colloidal substances and the agglomeration / fixed organic substances other than biopolymers that are not detected by UV 260 are released.

Further, from the SFF and MFF in FIG. 4A, the proper aggregation pH range in which the optimum result is obtained is determined to be 5.7 to 6.5 even when FeCl _{3 is used} alone.
When the pH is 6.5 or more, the biopolymer presence index SFF increases and the fine particle presence index MFF greatly increases as the pH increases.
An increase in SFF is interpreted as a re-elution of the biopolymer once captured by NaOH.
The large increase in MFF is interpreted as a part of the aggregated floc containing biopolymer was separated by iron hydroxide together with NaOH and dispersed colloidally.

In the case of FeCl ₃ alone shown in FIG. 4 and in the case of combined use of BP 201 shown in FIG. 3, the same tendency is shown, but the difference between the two is as follows.
(1) Achieved SFF1.05 at pH 5.7 to 6.5 in the case of FeCl ₃ alone in FIG. 4 (a) is one rank lower than achieved SFF1.00 in the case of combined use with BP201 in FIG. 3 (a). It is evaluation. That is, a better result can be obtained when BP201 is used together.
(2) The degree of deterioration of MFF at pH 7 or higher is larger in the case of using BP201 in FIG. This is presumably because the secondary reaction phenol resin itself dissolves in NaOH, so that the degree to which the incorporated pollutant is released is greater than when the secondary reaction phenol resin is not added.

It can be judged that the deterioration of water quality at a coagulation pH of 6.5 or more occurs when free OH ⁻ remains for a relatively long time and the contaminant once trapped by the coagulation action of the trivalent iron inorganic coagulant is peeled off again.
The peeled off contaminants are partially dispersed in the water in the form of a colloidal or microgel containing the original soluble contaminants and the majority including the original soluble contaminants. The particle diameter of the fine particle component is presumed to be less than about 1 μm, and solid-liquid separation by precipitation and levitation is impossible. In addition, it is difficult to capture with a gravity type two-layer filtration device.
Is also the same phenomenon occurs in less than aggregation pH 6.5, min pH is low, but may be re-condensed to remain more is condensation action of trivalent iron inorganic coagulant, free OH meantime ^- decreasing the velocity is large, the water Deterioration is unlikely to occur.

When the proper coagulation pH range was examined for the biologically treated water in each liquid crystal factory in the same manner as in Experimental Examples 1 and 2, the following results were obtained. From these results, the difference between the aggregation lower limit pH and the pH at which NaOH destruction of the aggregate occurs, that is, the proper pH range width is 0.8 to 1.0 pH.
Factory A: pH 5.7-6.5
Factory B: pH 5.8 to 6.6
Factory C: pH 4.9 to 5.8
Factory D: pH 4.8-5.8 *
Factory D: pH 4.7-5.5 *
Factory E: pH 4.5-5.5
(* Liquid crystal D factory evaluated each of two different types of biologically treated water.)

[Experimental example 3: Confirmation of detachment of phenolic resin from aggregates by NaOH]
The phenol-based resin alkaline solution purifies water in the water to be treated having a neutral level or less by insolubilizing the resin component, combining the insolubilized product with the biopolymer, and insolubilizing the biopolymer together.
Therefore, if a local high pH is generated with NaOH, the reaction between the phenolic resin and contaminants such as biopolymers is weakened, and the phenolic resin component itself is dissolved.

The experimental results showing this will be shown below.
A reaction solution prepared by adding 10 mg / L of BP201 to Nogi-cho tap water in Tochigi Prefecture, which was adjusted to a predetermined pH in advance, was reacted. For filtered water filtered with 5A filter paper (however, only one filter paper was used), the BP201 concentration leaked from the filtered water was tested from the absorbance increases at 280 nm and 270 nm, which are absorption peak wavelengths in the ultraviolet region of BP201, and the leak rate Was calculated as a percentage. The results are shown in FIG.
As is apparent from FIG. 5, 90% of the insoluble matter that can be filtered is generated at pH 6 or lower, whereas resin components that cannot be filtered out from pH 6.5 start to increase, and filter paper at pH 7 to 7.5. The component that permeates through increases rapidly to 90%.
Since the component which permeate | transmits this filter paper is detected as micro turbidity (netNTU), it is thought that it is not completely dissolved but partially colloidal.
Considering the relationship with FIG. 3 above, the reaction product of the pollutant such as biopolymer and the phenolic resin, which has been incorporated into the iron hydroxide floc, is peeled off by OH ⁻ which brings about a high local pH, and colloidal. In addition, a part thereof is in a dissolved state and is dispersed or dissolved on the liquid side.
Since the local high pH was finally eliminated and the iron coagulation force was already lost even when the pH was 6.5 or lower, the colloidal material could not be recondensed, and the fine particles of filtered water were It is presumed that more remains than in the case of FeCl ₃ alone.

[Comparative Example 1, Example 1]
The present invention was verified using a coagulation facility for biologically treated water (appropriate coagulation pH range = 5.8 to 6.6) of the waste water of the liquid crystal B factory.
The treatment process is as follows, and the evaluation was performed by measuring the MFF of the RO membrane supply water (filtered water) once a day and obtaining the average value.
Wastewater → Biological treatment → Water tank to be treated (BP201 added 6.0 mg / L) → Inorganic flocculant reaction tank (with trivalent iron inorganic flocculant and NaOH addition equipment) → Neutralization / coagulation tank (with NaOH addition equipment) → Flotation separation device → gravity type two-layer filtration device → recovery facility by RO membrane separation device As the trivalent iron-based inorganic flocculant, FeCl ₃ was used, and the average addition amount was 90 mg / L. Moreover, the control target pH value of the inorganic flocculant reaction tank was set to 6.0, and the control target pH value of the neutralization / coagulation tank was set to 6.4. The average value of MFF of RO membrane feed water for 7 days was 1.086 (Comparative Example 1).
Thereafter, the FeCl ₃ average addition amount 85 ppm, the inorganic flocculant reaction tank pH control target pH value 6.2, the neutralization / coagulation tank control target pH value 6.0, and the neutralization / coagulation tank control target pH value is set to the inorganic flocculant When set to 0.2 lower than the reaction tank, the average value of MFF of RO membrane feed water for the subsequent 7 days is 1.050, and even if the amount of FeCl ₃ added is reduced, the membrane filterability index MFF is improved. (Example 1).

[Comparative Example 2, Example 2]
The present invention was verified in a coagulation facility for biologically treated water (appropriate coagulation pH range = 4.9 to 5.8) of the wastewater of the liquid crystal C factory.
There were three treatment series, one of which was the control system (Comparative Example 2), and another series was the implementation system of the present invention (Example 2).
The treatment process is as follows, and the evaluation is carried out by collecting the treated water of the flotation separation device and performing No. About filtered water obtained by filtering with 5A filter paper, it performed by measuring SFF and MFF 3 times and calculating | requiring the average value.
Wastewater → Biological treatment → Water tank to be treated → Inorganic flocculant reaction tank (with trivalent iron inorganic flocculant and NaOH addition equipment) → Neutralization / coagulation tank (with NaOH addition equipment) → Floating separator → Gravity type two-layer filtration equipment → Recovery facility by RO membrane separator Polyferric sulfate was used as the trivalent iron-based inorganic flocculant, and the average addition amount was 120 ppm.
When the control target pH value of the inorganic flocculant reaction tank of the control series was set to 4.0 and the control target pH value of the neutralization / flocculation tank was set to 5.2, SFF = 1.093, MFF = 1.113, The average pH of the levitated water was 5.2 (Comparative Example 2).
On the other hand, when the present invention implementation system was set to the inorganic flocculant reaction tank control target pH value of 5.2 and the neutralization / coagulation tank control target pH value of 5.0, SFF = 1.082 and MFF = 1.089. The average levitation treatment water pH was 5.1 (Example 2).

[Comparative Example 3, Example 3]
5 mg / L of BP201 was added to the water tank to be treated in the agglomeration facility for biologically treated water (appropriate agglomeration pH range = 4.9 to 5.8) of the liquid crystal C factory waste water in Comparative Example 2 and Example 2 above. In the same manner, the control target pH values of the respective tanks were similarly verified.
In Example 3, the SFF and MFF were measured in the same manner as described above, and the MFF of RO membrane feed water was also measured in the same manner as in Example 1.
As a result, in Comparative Example 3 in which the inorganic flocculant reaction tank control target pH value was set to 4.0 and the neutralization / coagulation tank control target pH value was set to 5.2, the surface floated at SFF = 1.053 and MFF = 1.088. The average pH of the treated water was 5.3.
On the other hand, in Example 2 in which the inorganic flocculant reaction tank control target pH value was set to 5.2 and the neutralization / coagulation tank control target pH value was set to 5.0, the levitation treatment was performed with SFF = 1.014 and MFF = 1.038. The average pH of water was 5.1, and the average value of MFF of RO membrane feed water for 7 days was 1.086.

  As described above, in Example 2 in which the phenolic resin alkaline solution is not used and also in Example 3 in which the phenolic resin alkaline solution is used in combination, the control target pH value of each tank is set according to the present invention. Compared with the comparative example of the conventional method, the RO membrane contamination index of the agglomerated / filtered water is reduced, and particularly when the phenolic resin alkaline solution is used in combination, the effect of the present invention is remarkable.

1 First reactor (inorganic flocculant reactor)
2 Second reaction tank (neutralization / coagulation tank)
3 Floating separation device 4 Filtration device 5 RO membrane separation device 10 Controller

Claims (12)

In the first reaction tank provided with the trivalent iron-based inorganic flocculant and NaOH added in series, and the second reaction tank, the water to be treated is sequentially passed to the flocculant,
The second reaction tank is a tank that is not added with an aggregating agent and is agglomerated without addition of alkali or with a very small amount of NaOH.
When the lower limit pH value of the pH range in which aggregated flocs are formed in the water to be treated by adding the trivalent iron-based inorganic flocculant and performing the aggregation treatment is X,
The control target pH value A of the second reaction tank is set in the range of X to (X + 0.3),
A coagulation treatment method characterized in that the coagulation treatment is performed by setting the control target pH value A ′ of the first reaction tank to a range of A to (A + 0.7).   In claim 1, the first reaction tank is adjusted so that the pH value in the first reaction tank is the control target pH value A 'and the pH value in the second reaction tank is the control target pH value A. An agglomeration method comprising adding NaOH to the reaction vessel.   In Claim 1, NaOH is added to the first reaction tank so that the pH value in the first reaction tank becomes the control target pH value A ', and the pH value in the second reaction tank is An agglomeration method, wherein NaOH is added to the second reaction tank so as to achieve the control target pH value A.   The flocculation process according to any one of claims 1 to 3, wherein a water-soluble polymer having a phenolic hydroxyl group is added prior to adding the trivalent iron-based inorganic flocculant to the water to be treated. Method.   The aggregation treatment method according to claim 1, wherein the water to be treated is biologically treated water.   A water treatment method, comprising subjecting the agglomerated water obtained by the agglomeration treatment method according to any one of claims 1 to 5 to solid-liquid separation and then a reverse osmosis membrane separation treatment. A first reaction tank and a second reaction tank provided in series;
Means for sequentially passing water to be treated into the first reaction tank and the second reaction tank;
A trivalent iron-based inorganic flocculant addition means and NaOH addition means provided in the first reaction tank;
First pH control means for controlling the pH of the first reaction tank to a control target pH value A ′;
A coagulation treatment apparatus having a second pH control means for controlling the pH of the second reaction tank to a control target pH value A,
The second reaction tank is a tank that is not added with an aggregating agent and is agglomerated without addition of alkali or with a very small amount of NaOH.
When the lower limit pH value of the pH range in which aggregated flocs are formed in the water to be treated by adding the trivalent iron-based inorganic flocculant and performing the aggregation treatment is X,
The control target pH value A of the second reaction tank is set in the range of X to (X + 0.3),
The control target pH value A ′ of the first reaction tank is set in a range of A to (A + 0.7).   In Claim 7, NaOH addition means of said 1st reaction tank is NaOH addition amount by said 1st pH control means so that pH value in this 1st reaction tank may become said control target pH value A '. And the addition amount of NaOH is controlled by the second pH control means so that the pH value in the second reaction tank becomes the control target pH value A. .   In Claim 7, NaOH addition means is provided in the second reaction tank, and the NaOH addition means of the second reaction tank is such that the pH value in the second reaction tank is equal to the control target pH value A. The NaOH addition amount is controlled by the second pH control means, and the pH value in the first reaction tank is the control target pH value A ′ in the NaOH addition means of the first reaction tank. Thus, the amount of NaOH added is controlled by the first pH control means.   The agglomeration treatment according to any one of claims 7 to 9, further comprising means for adding a water-soluble polymer having a phenolic hydroxyl group to the water to be treated in the previous stage of the first reaction tank. apparatus.   The aggregation treatment apparatus according to claim 7, wherein the water to be treated is biologically treated water.   The coagulation treatment apparatus according to any one of claims 7 to 11, solid-liquid separation means for solid-liquid separation of the coagulation treatment water obtained by the coagulation treatment apparatus, and obtained by the solid-liquid separation means A water treatment apparatus, comprising: a reverse osmosis membrane separation device for subjecting separated water to a reverse osmosis membrane separation treatment.

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