JP2004267830A - Method for treating biological treatment water-containing water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform stable treatment over a long period of time by preventing the lowering of the flux of an RO membrane, in subjecting biological treatment water-containing water to RO treatment. <P>SOLUTION: The biological treatment water-containing water is adjusted to pH 4-6 to be filtered and the obtained filtered water is subjected to RO treatment. Since protein or the like causing the lowering of the flux of the RO membrane is easily flocculated in the vicinity of pH 4-6, a substance causing the lowering of the flux of the RO membrane such as protein or the like contained in the biological treatment water-containing water can be efficiently trapped and removed by a filter by passing the biological treatment water-containing water adjusted to pH 4-6 through the filter to suppress the lowering of the flux of the RO membrane. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for purifying water containing biologically treated water by reverse osmosis (RO) membrane separation treatment, and more particularly, to a method for performing a stable treatment by preventing a reduction in permeation flux of an RO membrane. The present invention relates to a method for treating treated water-containing water.
[0002]
[Prior art]
In recent years, environmental standards and water quality standards have become stricter, and it is desired to highly purify discharged water. On the other hand, advanced water treatment is desired to collect and reuse various wastewaters for the purpose of eliminating water shortages.
[0003]
Under such circumstances, the reverse osmosis membrane separation treatment (hereinafter referred to as “RO treatment”) can efficiently remove impurities (ions, organic substances, fine particles, etc.) in water. In many cases, it is used for secondary treatment of wastewater. For example, when recovering and reusing high-concentration TOC or low-concentration TOC wastewater containing acetone, isopropyl alcohol, and the like discharged from a semiconductor manufacturing process, this is firstly biologically treated to remove the TOC component, and the biologically treated water is removed. A method of purifying by RO treatment is employed.
[0004]
Conventionally, as the RO film used for the RO treatment, a wholly aromatic crosslinked polyamide-based composite film (PA film), a cellulose acetate film (CA film), and the like have been provided. In the RO treatment, in order to prevent a decrease in the flux and perform a stabilization treatment, a standard for water to be treated (water supply) supplied to an RO membrane separation device (hereinafter abbreviated as “RO device”) is set. And it is desired that the FI (Fouling Index) value be 4 or less. This FI value is a standard for water supply to the RO device determined by the RO membrane maker, and indicates that the smaller the FI value, the smaller the load on the membrane and the lower the flux is.
[0005]
Among the conventional RO films, the PA film is stable because the film is contaminated by the adsorption of a trace amount of a fouling substance such as a surfactant or a protein contained in the water to be treated, and the flux is rapidly reduced. Cannot be continued. The CA membrane has better contamination resistance than the PA membrane, but has problems such as a low desalting rate and a high operating pressure.
[0006]
In recent years, RO membranes (uncharged membranes) have been developed in which the membrane is hardly soiled by eliminating charge on the membrane surface and improving hydrophilicity. In addition, when treating water containing a relatively high viscosity component such as protein, the effect of stain resistance is low, and there is also a problem that the flux decreases with time.
[0007]
Therefore, in the RO treatment of biologically treated water, it is conceivable to remove in advance a fouling substance having a relatively high viscosity, such as a protein, by filtration. However, these substances are very small. It flows into the RO device without being caught by the vessel and causes clogging of the membrane.
[0008]
In particular, in the biological treatment step, an excessive amount of a phosphorus-containing drug is added as a nutrient for biodegradation in many cases, so that the concentration of phosphorus in the biological treatment water tends to increase. Phosphorus has the property of inhibiting coagulation, so that a large amount of coagulant must be added to obtain filtered water of FI4 or less by coagulating and filtering water containing biologically treated water. Therefore, in this case, the cost of chemicals increases and the filter must be backwashed frequently. In addition, since the water containing biologically treated water has large fluctuations in water quality, the optimum amount of the coagulant added changes each time, and it is difficult to properly control the amount. For this reason, if the amount is too small, the quality of the resulting filtered water is poor. Conversely, if the amount is excessive, the excessively added flocculant itself causes clogging of the RO membrane.
[0009]
For this reason, when performing RO treatment on biologically treated water-containing water, in order to prevent a reduction in the flux of the RO membrane, prior to the RO treatment, even if an attempt is made to filter and remove the flux-reducing factor substance in the biologically treated water, a conventional method has been used. However, it was not possible to prevent a decrease in the flux of the RO membrane because the removal itself by filtration was difficult.
[0010]
[Problems to be solved by the invention]
The present invention solves the above-mentioned conventional problems, and provides a method for performing a long-term stable treatment by preventing a decrease in the flux of an RO membrane in RO treatment of water containing biologically treated water. The purpose is to do.
[0011]
[Means for Solving the Problems]
The method for treating biologically treated water-containing water of the present invention is a method for treating biologically treated water-containing water, wherein RO-treated water containing biologically treated water is adjusted to pH 4 to 6 and filtered. And RO treatment of the obtained filtered water.
[0012]
The inventor of the present invention has focused on the fact that when performing RO treatment on water containing biologically treated water, the factor that lowers the flux of the RO membrane is a component having relatively high tackiness such as proteins, and suppresses the reduction in flux due to these proteins and the like. As a result of examining a simple method to carry out the treatment, it was found that by adjusting the pH of the water containing biologically treated water to pH 4 to 6 and filtering the same, it is possible to prevent a reduction in the flux of the RO membrane for the following reasons.
[0013]
That is, the protein that causes the flux reduction in the water containing biologically treated water has an isoelectric point near pH 4.5 to 5.5. The isoelectric point means a pH at which the potential of the surface becomes zero, and by adjusting the pH around this, an agglutinating action occurs on proteins and similar substances. Therefore, by passing water adjusted to pH 4 to 6 near the isoelectric point through a filter, flux-reducing factors such as proteins contained in the biologically treated water-containing water are efficiently captured and removed by the filter. This makes it possible to suppress a reduction in the flux of the RO film.
[0014]
In the present invention, in order to perform more efficient processing, it is preferable to employ the following means.
{Circle around (1)} By adding a coagulant to the water to be filtered, coagulation and filtration are performed to enhance the coagulation effect of a flux-reducing factor substance such as a protein.
{Circle around (2)} A chlorinating agent is added to the water to be filtered to suppress the growth of slime in the filter and enhance the coagulation effect.
{Circle around (3)} A scale dispersant is added to the filtered water to be subjected to RO treatment to prevent scale deposition in the RO device and to maintain a high membrane flux.
{Circle around (4)} A slime control agent is added to the filtered water to be subjected to RO treatment to suppress the propagation of slime in the RO device, and maintain a high membrane flux.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of a method for treating biologically treated water-containing water of the present invention will be described in detail with reference to the drawings.
[0016]
FIG. 1 is a system diagram showing an embodiment of the method for treating water containing biologically treated water of the present invention.
[0017]
In FIG. 1, a chlorinating agent, an acid and a flocculant are added to the biologically treated water-containing water, filtered by a filter 1, and a scale dispersant and a slime control agent are added to the obtained filtered water, and the RO To process.
[0018]
The biologically treated water-containing water to be treated in the present invention is not particularly limited as long as it is treated water obtained by performing biological treatment or water containing the biologically treated water. Therefore, the biologically treated water containing TOC-containing water from the above-described semiconductor manufacturing process and the various biologically treated water-containing water such as comprehensive wastewater into which such biologically treated water flows can be treated.
[0019]
Since these biologically treated water-containing water is generally about pH 6.5-7.5, in the present invention, acid biologically treated water-containing water, for example, hydrochloric acid (HCl), and the like sulfuric acid _(H 2 SO ₄₎ Adjust to pH 4-6 by addition. Even if the adjusted pH exceeds 6 or is less than 4, the protein departs from the isoelectric point of the protein, so that the cohesiveness of the protein is deteriorated, and these flux lowering substances flow out of the filter 1. In particular, when the pH is 3 or less, a problem of corrosion of the apparatus occurs, which is not preferable.
[0020]
Although a flocculant is not always required, aggregation can be promoted by adding a flocculant. As the coagulant, ferric chloride (FeCl ₃ ), ferric sulfate (Fe ₂ (SO ₄ ) ₃ ), or the like that is effective in a pH range of ₄ to 6 can be used. The amount of the coagulant to be added is preferably about 1 to 50 mg / L with respect to the water containing biological treatment water, from the viewpoint of the coagulation effect of proteins and the like.
[0021]
Although a chlorine agent is not necessarily required, the addition of the chlorine agent can suppress slime propagation in the filter 1 and improve cohesion. As the chlorinating agent, sodium hypochlorite (NaClO) or the like can be used, and it is effective to add the chlorinating agent so that the residual chlorine concentration of the obtained filtered water is about 0.1 to 5 mg / L. It is a target.
[0022]
There are no particular restrictions on the order in which the acid, coagulant and chlorine agent are added for pH adjustment.
[0023]
In the present invention, the filtration means for the biologically treated water-containing water is not particularly limited. In addition to the filter 1 such as a membrane filter or an activated carbon filter, a means such as sedimentation filtration and pressure flotation filtration may be employed. Can be.
[0024]
The filtered water is then subjected to an RO treatment by the RO device 2. Prior to the RO treatment, it is preferable to add a scale dispersing agent and a slime control agent to the filtered water to prevent a decrease in membrane flux due to scale and slime. In this case, as the scale dispersant, a hexametaphosphoric acid type, acrylic acid type, phosphonic acid type, etc. scale dispersant can be used, and the amount of the dispersant is about 1 to 20 mg / L with respect to the filtered water. Is preferred. Further, as the slime control agent, a non-oxidizing slime control agent such as an isothiazoline type (for example, 2-methyl-4-isothiazolin-3-one) is preferable. It is preferably about L.
[0025]
The pH of the feed water of the RO device is preferably pH 6 or less from the viewpoint of suppressing the precipitation of calcium-based scales such as CaCO ₃ and Ca ₃ (PO ₄ ) ₂ in the RO device. Since the biologically treated water-containing water is adjusted to pH 4 to 6 and filtered, the obtained filtered water can be subjected to RO treatment without pH adjustment.
[0026]
There is no particular limitation on the RO film of the RO device, and in the present invention, any of the above-described PA film, CA film, and uncharged film can be used to prevent a decrease in the flux of each film. In general, the degree of reduction of the flux is larger in the order of the CA film, the uncharged film, and the PA film. In the present invention, the flux can be maintained higher by using the CA film or the uncharged film. .
[0027]
FIG. 1 shows an example of an embodiment of a method for treating water containing biologically treated water according to the present invention, and the present invention is not limited to the illustrated method unless it exceeds the gist. For example, the RO device can be arranged in series in two or more stages to perform advanced treatment by multi-stage RO treatment. At that time, the pH of the feed water of the second and subsequent RO devices is adjusted to alkaline. Means such as enhancing the effect of removing the carbonic acid component may be employed.
[0028]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Experimental Examples, Examples, and Comparative Examples.
[0029]
Experimental example 1
Using treated water (pH 7) obtained by treating wastewater from a semiconductor manufacturing plant with a biological filtration device as biologically treated water-containing water, a necessary amount of acid (HCl) or alkali (NaOH) is added to the biologically treated water-containing water. Then, the mixture was filtered with a two-layer filter using anthracite and sand as filter media.
[0030]
The FI value of the obtained filtered water was measured, and the results are shown in FIG.
[0031]
From FIG. 2, it can be seen that a good RO membrane water supply with an FI value of 4 or less can be obtained by adjusting the pH of the biologically treated water-containing water to 4 to 6 and filtering.
[0032]
Example 1
Using treated water (pH 7) obtained by treating wastewater from a semiconductor manufacturing plant with a biological filtration device as biologically treated water-containing water, adjusting the pH of the biologically treated water-containing water to pH 5 by adding HCl, The mixture was filtered with a two-layer filter using sand as a filter medium. 10 mg / L of a phosphonic acid-based dispersant ("Kuriflot D-170" manufactured by Kurita Kogyo) and an isothiazoline-based slime control agent ("Criverta EC-503" manufactured by Kurita Kogyo Co., Ltd.) are added to the obtained filtered water (pH 5). After adding 3 mg / L, RO treatment was performed using a RO device (Nitto Denko Corporation, uncharged low-contamination membrane “LF-10”) at a recovery rate of 50%.
[0033]
At this time, the change with time of the flux of the RO device was examined, and the results are shown in FIG.
[0034]
Comparative Example 1
In Example 1, the treatment was performed in the same manner as in Example 1, except that the water containing the biologically treated water was directly supplied to the filter without pH adjustment, and HCl was added to the obtained filtered water to adjust the pH to 5, followed by RO treatment. Then, the time-dependent change of the flux of the RO apparatus was examined, and the results are shown in FIG.
[0035]
As is clear from FIG. 3, in Example 1, almost no decrease in the flux was observed even after 48 hours from the start of water flow, whereas in Comparative Example 1, the flux decreased by about 14% from the initial flux in the same elapsed time. .
[0036]
From the above results, according to the present invention, the water containing biologically treated water is adjusted to pH 4 to 6, filtered, and then subjected to RO treatment, thereby preventing a decrease in the flux of the RO membrane and performing stable RO treatment for a long period of time. You can see that you can do it.
[0037]
【The invention's effect】
As described above in detail, according to the method for treating biologically treated water-containing water of the present invention, when RO containing water containing biologically treated water is subjected to advanced treatment, the flux of the RO film is prevented from lowering, , Stable processing can be performed.
[Brief description of the drawings]
FIG. 1 is a system diagram showing an embodiment of a method for treating water containing biologically treated water of the present invention.
FIG. 2 is a graph showing the relationship between the feedwater pH of a filter and the FI value of filtered water in Experimental Example 1.
FIG. 3 is a graph showing the change over time of the flux in Example 1 and Comparative Example 1.
[Explanation of symbols]
1 Filter 2 RO device

Claims (1)

A method for treating biologically treated water containing water, which comprises reverse osmosis membrane separation of water containing biologically treated water,
A method for treating water containing biologically treated water, wherein the water containing biologically treated water is adjusted to pH 4 to 6, filtered, and the resulting filtered water is subjected to reverse osmosis membrane separation treatment.

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