JP2007253073A - Apparatus and method for treating water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus and a method for treating water, in each of which when the water which is to be treated contains a BOD component and a polyvalent inorganic cation, is treated by using an RO membrane separation unit and the treated water is recovered, the decrease of a flux and the biofouling, each of which is caused by the adhesion of organic matter onto the surface of a membrane in the PO membrane separation unit, are prevented and a COD value of RO concentrated water is decreased efficiently to prevent a bad influence of the RO concentrated water on waste water treatment. <P>SOLUTION: A biodegradable scale inhibitor and an alkali are added to the water to be treated to adjust the pH of the water to be treated to ≥9.5. The resulting water is made to pass through the RO membrane separation unit 4. The RO concentrated water is treated biologically. Since the pH of the water to be supplied to the RO membrane separation unit is adjusted to ≥9.5, the biofouling in the RO membrane separation unit can be prevented, the adhesion of a nonionic surfactant onto the surface of the membrane can be prevented and the decrease of the flux can also be prevented. The clogging of the membrane surface by calcium carbonate scale under a high pH condition is restrained by adding the scale inhibitor. Since the RO concentrated water is treated biologically by using the biodegradable scale inhibitor and the biodegradable scale inhibitor in the RO concentrated water is biodegraded, TOC can be decreased. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention provides a RO membrane when treating and recovering water to be treated containing BOD components such as waste water discharged from an electronic device manufacturing factory and the like and a polyvalent inorganic cation using a reverse osmosis (RO) membrane separation device. Prevents decrease in flux due to adhesion of organic substances in the separator and biofouling for stable treatment over a long period of time, and at the same time efficiently reduces the TOC concentration in water to obtain high-quality treated water The present invention also relates to a water treatment apparatus and a water treatment method for easily and efficiently treating concentrated water of an RO membrane separation apparatus.

  In recent years, environmental standards and water quality standards tend to be stricter, and it is desired to purify discharged water to a high degree. On the other hand, for the purpose of eliminating water shortage, development of advanced water treatment technology is also desired in order to collect and reuse various wastewater.

  Under such circumstances, RO membrane separation treatment can effectively remove impurities (ions, organic substances, fine particles, etc.) in water, and has recently been used in many fields. It was. For example, when recovering and recycling wastewater containing high-concentration TOC or low-concentration TOC containing acetone, isopropyl alcohol, etc. discharged from the semiconductor manufacturing process, this is first biologically treated to remove the TOC component, A method of purifying by RO membrane treatment is widely adopted (for example, JP-A-2002-336886).

  However, in recent years, when biological treatment wastewater is passed through the RO membrane separation device, the problem that the membrane surface of the RO membrane is clogged and the flux decreases due to biological metabolites generated by the decomposition of organic matter by microorganisms begins to become apparent. It has become like this.

  On the other hand, when these TOC-containing wastewater is directly passed through the RO membrane separator without using biological treatment, the TOC concentration flowing into the RO membrane separator is high, so that microorganisms propagate in the RO membrane separator. Easy environment. Therefore, for the purpose of suppressing biofouling in the RO membrane separation apparatus, a large amount of slime control agent is usually added to TOC-containing wastewater. However, since the slime control agent is expensive, it is cheaper. There is a need for a new biofouling suppression method.

  In addition, the wastewater discharged from the electronic device manufacturing factory may be mixed with a nonionic surfactant that may adhere to the membrane surface of the RO membrane separator and reduce the flux. RO membrane separation treatment could not be applied to such nonionic surfactant-containing wastewater.

  When solving such problems and treating and collecting wastewater containing high or low concentration organic matter discharged from electronic device manufacturing factories and other various fields using RO membrane separators, As a technology to obtain high-quality treated water by efficiently reducing the TOC concentration in water while simultaneously performing stable treatment over a long period of time by preventing flux reduction and biofouling due to the adhesion of the organic material to the film surface First, add to the organic matter-containing wastewater an alkali to the organic matter-containing wastewater as well as adding a scale inhibitor at least 5 times the weight of calcium ions in the organic matter-containing wastewater. Thus, a method and apparatus for adjusting the pH to 9.5 or higher and then performing RO separation treatment have been proposed (Japanese Patent Laid-Open No. 2005-169372).

  In this way, RO membrane separation is performed by adding a predetermined amount of scale inhibitor to the water to be treated (hereinafter sometimes referred to as “RO feed water”) introduced into the RO membrane separation device and adjusting the pH to 9.5 or higher. By passing the water through the device, the following actions and effects can be performed for a long period of time to prevent a decrease in flux due to adhesion of the membrane surface of organic matter in the RO membrane separator and biofouling, and to perform stable treatment over a long period of time. It is possible to efficiently reduce the TOC concentration in water and obtain high quality treated water.

(1) The following effects can be obtained by adjusting the pH of the RO water supply to 9.5 or higher.
Microorganisms cannot live in alkaline areas. Therefore, by adjusting the pH of the RO feed water to 9.5 or more, it becomes possible to create an environment in which there are nutrient sources but microorganisms cannot live in the RO membrane separation device. Biofouling in the RO membrane separator can be suppressed without the need for addition.
In addition, nonionic surfactants that may lower the flux are known to be desorbed from the membrane surface in the alkaline region. By increasing the pH of the RO water supply to 9.5 or higher, these are applied to the RO membrane surface. It becomes possible to suppress adhesion of these components.

(2) The following effects can be obtained by adding a scale inhibitor 5 times or more times the calcium ion in the RO water supply to the RO water supply.
In rare cases, TOC-containing wastewater discharged from an electronic device manufacturing factory or the like may be mixed with polyvalent inorganic cations such as calcium ions, which are the basis of scale. Under high pH RO operating conditions where the pH of the RO feed water is 9.5 or higher, even if a very small amount of polyvalent inorganic cation is mixed, scales such as calcium carbonate are generated and the RO membrane is immediately clogged. Therefore, for the purpose of suppressing the membrane surface clogging due to such scale, a scale inhibitor is added to the RO water supply at least 5 times the weight of calcium ions in the RO water supply to prevent the generation of scale.
JP 2002-336886 A JP 2005-169372 A

  According to the technique described in Japanese Patent Application Laid-Open No. 2005-169372, wastewater containing high or low concentration organic substances discharged from electronic device manufacturing factories and other various fields, particularly wastewater containing nonionic surfactants, is RO membrane. When processing / recovering using a separator, the TOC concentration in the water is efficient while at the same time providing stable treatment over a long period of time by preventing flux reduction and biofouling due to the adhesion of the organic matter in the RO membrane separator. However, there are the following problems.

  That is, in accordance with the technique described in JP-A-2005-169372, concentrated water obtained by adding a scale inhibitor to RO water supply and performing RO membrane separation treatment (hereinafter sometimes referred to as “RO concentrated water”). Concentrates the added scale inhibitor, so that it contains a large amount of the scale inhibitor that is a COD component. That is, since the scale inhibitor does not permeate the RO membrane, it is concentrated on the concentrated water side. In particular, according to the technique of Japanese Patent Application Laid-Open No. 2005-169372, a large amount is contained in the RO concentrated water obtained by adding a large amount of scale inhibitor more than 5 times the weight of calcium ions in the RO feed water and subjecting it to RO membrane separation treatment. The scale preventive agent is included.

  Usually, RO concentrated water is transferred to a wastewater treatment process and discharged through biological treatment and coagulation sedimentation treatment. In general, scale inhibitors are difficult to remove by coagulation sedimentation treatment and biological treatment. The inhibitor also inhibits the aggregation reaction. Therefore, when RO concentrated water containing a large amount of scale inhibitor is transferred to the wastewater treatment process, the load of the wastewater treatment process is increased and the COD value in the discharged water is increased, thereby reducing the water quality. There is a fear.

  Therefore, an object of the present invention is to provide a water treatment apparatus and a water treatment method that efficiently reduce the scale inhibitor of RO concentrated water and prevent adverse effects on the drainage treatment of RO concentrated water and the like. .

  The water treatment apparatus of the present invention (Claim 1) is a scale in which a biodegradable scale inhibitor that suppresses scaling of the polyvalent inorganic cation is added to the water to be treated containing the BOD component and the polyvalent inorganic cation. An inhibitor adding means, a pH adjusting means for adjusting the pH of the water to be treated to 9.5 or more by adding an alkali to the water to be treated before, after or simultaneously with the addition of the scale inhibitor, and the scale inhibitor A reverse osmosis membrane separation means for separating the treated water that has passed through the addition means and the pH adjustment means into permeated water and concentrated water; and a biological treatment means for treating the BOD component contained in the concentrated water. Features.

  The water treatment apparatus according to claim 2 is characterized in that, in claim 1, the water to be treated is a part of the treated water of the biological treatment means.

  The water treatment apparatus according to claim 3 is the scale according to claim 1 or 2, wherein the scale inhibitor addition means includes, in the treated water, a scale that is at least 1/10 times the total polyvalent inorganic cation content in the treated water. It is characterized by adding an inhibitor.

  The water treatment device according to claim 4 is the water treatment device according to any one of claims 1 to 3, wherein the reverse osmosis membrane of the reverse osmosis membrane separation device is 1500 mg / L of saline at 1.47 MPa, 25 ° C., pH 7. It is characterized by being a polyvinyl alcohol-based low fouling reverse osmosis membrane having a desalting performance of 95% or more when the reverse osmosis membrane separation treatment is carried out.

  A water treatment device according to a fifth aspect is characterized in that, in any one of the first to fourth aspects, the pH adjusting means adjusts the pH of the water to be treated to 10.5 to 12.

  The water treatment device according to claim 6 is characterized in that, in any one of claims 1 to 5, the water treatment device has means for adjusting the pH to 5 to 8 by adding an acid to the concentrated water introduced into the biological treatment means. To do.

  The water treatment method of the present invention (invention 7) is a scale in which a biodegradable scale inhibitor that suppresses scaling of the polyvalent inorganic cation is added to the water to be treated containing the BOD component and the polyvalent inorganic cation. An inhibitor adding step, a pH adjusting step of adjusting the pH of the water to be treated to 9.5 or more by adding an alkali to the water to be treated before, after or simultaneously with the addition of the scale inhibitor, and the scale inhibitor A reverse osmosis membrane separation step of supplying treated water that has undergone the addition step and pH adjustment step to a reverse osmosis membrane separation device and separating it into permeated water and concentrated water, and a organism that processes the BOD component contained in the concentrated water And a processing step.

  The water treatment method of claim 8 is characterized in that, in claim 7, the treated water is a part of treated water in the biological treatment process.

  A water treatment method according to claim 9 is the water treatment method according to claim 7 or 8, wherein, in the scale inhibitor addition step, the water to be treated has a scale that is 1/10 times or more times the total content of polyvalent inorganic cations in the water to be treated. It is characterized by adding an inhibitor.

  A water treatment method according to a tenth aspect is the water treatment method according to any one of the seventh to ninth aspects, wherein the reverse osmosis membrane of the reverse osmosis membrane separator is 1500 mg / L of saline at 1.47 MPa, 25 ° C., pH 7. It is characterized by being a polyvinyl alcohol-based low fouling reverse osmosis membrane having a desalting performance of 95% or more when the reverse osmosis membrane separation treatment is carried out.

  The water treatment method according to claim 11 is characterized in that, in any one of claims 7 to 10, the pH adjusting means adjusts the pH of the water to be treated to 10.5 to 12.

  A water treatment method according to claim 12 is characterized in that, in any one of claims 7 to 11, the method comprises adjusting the pH to 5 to 8 by adding an acid to the concentrated water introduced into the biological treatment step. To do.

  According to the water treatment apparatus and water treatment method of the present invention, the water treatment apparatus and water treatment method include wastewater containing high or low concentration organic substances discharged from electronic device manufacturing factories and other various fields, particularly nonionic surfactants. When processing and recovering wastewater containing RO using a RO membrane separator, it is possible to perform stable treatment over a long period of time by preventing decrease in flux and biofouling due to the adhesion of organic substances to the membrane surface in the RO membrane separator. At the same time, high-quality treated water can be obtained by efficiently reducing the TOC concentration in water. Moreover, it is possible to easily and efficiently treat the organic substance containing the scale inhibitor in the RO concentrated water to reduce the load on the subsequent wastewater treatment process.

  That is, in the present invention, since the scale inhibitor is added to the RO water supply and the pH is adjusted to 9.5 or higher and water is passed through the RO membrane separator, as described above, biofouling in the RO membrane separator is performed. In addition, it is possible to suppress clogging of the film surface due to the scale.

  Moreover, in the present invention, since the biodegradable scale inhibitor is used as the scale inhibitor, the scale inhibitor in the RO concentrated water can be decomposed and removed by biological treatment at the subsequent stage.

  In addition, when a biodegradable scale inhibitor is used, it is a BOD component itself. Therefore, when RO membrane separation treatment is performed in a neutral pH range, the increase in the amount of scale inhibitor added in the RO membrane separator. Although the possibility of causing biofouling becomes very high, in the present invention, since the RO membrane separation treatment is performed in an alkaline region having a pH of 9.5 or higher as described above, such a problem does not occur.

  In the present invention, biological treatment of RO concentrated water can be performed by separately providing a biological treatment apparatus therefor. However, the biological treatment water discharged from an electronic device manufacturing factory and other various fields is treated with an RO membrane separation device. In this case, it is preferable that the RO concentrated water is returned to the biological treatment system upstream of the RO membrane separation device for biological treatment. That is, in this case, a part of the treated water obtained by biologically treating the RO concentrated water is supplied to the RO membrane separation device as treated water (claims 2 and 8).

In the present invention, if the amount of the scale inhibitor added to the water to be treated is too small, a sufficient scale prevention effect cannot be obtained, so the amount of the biodegradable scale inhibitor added to the water to be treated is It is preferable that the total content of polyvalent inorganic cations in the treated water is 1/10 times or more times (claims 3 and 9).
In the present invention, the amount of the scale inhibitor added is a value converted in the form of an acid even when the scale inhibitor is a salt such as a sodium salt.

  In the present invention, in particular, as the RO membrane, a salt rejection rate (hereinafter simply referred to as “salt exclusion rate”) when the RO membrane separation treatment is performed with 1500 mg / L of saline under the conditions of 1.47 MPa, 25 ° C., and pH 7. It is preferable to perform RO membrane separation treatment using a polyvinyl alcohol-based RO membrane for low fouling having a desalting performance of 95% or more. The reason why it is preferable to use such a low fouling RO membrane is as follows.

  That is, the low-fouling RO membrane is superior in contamination resistance because it eliminates the chargeability of the membrane surface and improves the hydrophilicity as compared with a commonly used aromatic polyamide membrane. However, with respect to water containing a large amount of nonionic surfactant, its antifouling effect is reduced, and the flux decreases with time.

  On the other hand, in the present invention, by adjusting the pH of the RO water supply to 9.5 or higher, the nonionic surfactant that may lower the RO membrane flux is desorbed from the membrane surface, so that an aromatic system that is usually used is used. Even when a polyamide film is used, it is possible to suppress an extreme decrease in flux. However, when the nonionic surfactant concentration in the RO water supply is high, the effect is also reduced, and the flux is lowered in the long term.

  Therefore, in the present invention, in order to solve such problems, preferably, the polyvinyl alcohol-based RO membrane for low fouling having the above-mentioned specific desalting performance and the pH of the RO water supply are 9.5 or more. In combination with the conditions for passing water, it is possible to perform stable operation over a long period of time without causing a decrease in flux even for RO water containing a high concentration of nonionic surfactant.

In the present invention, it is preferable to employ the following conditions in order to perform more efficient processing.
(1) The RO water supply pH is preferably 10.5 or more, particularly 10.5 to 12 (claims 5 and 11).
(2) The addition amount of the scale inhibitor is 1/10 to 5 times the polyvalent inorganic cation concentration.
(3) When the polyhydric inorganic cation concentration in the RO water supply is high, cation exchange treatment is performed as a pretreatment for adding the scale inhibitor to remove the polyvalent inorganic cation.
(4) An acid is added to the RO concentrated water to be biologically treated to adjust the pH to 5 to 8 (claims 6 and 12).

  Hereinafter, embodiments of a water treatment apparatus and a water treatment method of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a system diagram showing an embodiment of a water treatment apparatus and a water treatment method of the present invention.
In this embodiment, after biologically treating wastewater discharged from an electronic device manufacturing factory and other various fields in the biological treatment tank 1, a part of the treated water obtained by solid-liquid separation in the coagulation sedimentation tank 2 It is processed by the RO membrane separation device 4 as raw water (treated water containing BOD components and polyvalent inorganic cations) through the tank 3. In the biological treatment system of wastewater, a part of the separated sludge separated into solid and liquid in the coagulation sedimentation tank 2 is discharged out of the system as surplus sludge, and the remainder is returned to the biological treatment tank 1. A part of the separated water in the coagulation sedimentation tank 2 is sent to the tank 3 to be recovered and reused as service water, and the remaining part is drained out of the system. The raw water in the tank 3 is added with a biodegradable scale inhibitor and then added with alkali to a pH of 9.5 or higher, and then introduced into the RO membrane separator 4 and subjected to RO membrane separation treatment.

In the present invention, the polyvalent inorganic cation contained in the raw water to be treated is a cation that is insoluble in water and easily scaled, and is typically a divalent to trivalent cation. For example, Ca ²⁺ , Mg ^Examples include ions such as ²⁺ , Fe ³⁺ , and Al ³⁺ . These inorganic ions are scaled in the presence of counter ions that are easily insolubilized, such as hydroxide ions, carbonate ions, phosphate ions, and fluorine ions.

  Although there is no restriction | limiting in particular as a to-be-processed water containing such a polyvalent inorganic cation and a BOD component, For example, waste_water | drain of electronic device manufacture, such as liquid crystal factory waste_water | drain, semiconductor factory waste_water | drain, and various biological fields, and its biological treatment Water is mentioned.

There is no restriction | limiting in particular as a biodegradable scale inhibitor added to to-be-processed water, For example, polyaspartic acid, polyglutamic acid, polyalanine, polyleucine, polylysine, polyalginic acid etc. can be used. These biodegradable scale inhibitors may be used alone or in combination of two or more.
The scale inhibitor adheres to the surface of the fine scale crystal and suppresses the clogging of the RO membrane by suppressing the growth of nuclei. That is, the above chemical forms a complex with a metal ion, and it is possible to suppress the generation of scale with a small amount of addition, compared to a chelate scale inhibitor that suppresses the generation of scale.

  In the present invention, the addition amount of the scale inhibitor is preferably 1/10 times or more the content of polyvalent inorganic cations such as calcium ions in raw water (water to which the scale inhibitor is added). If the addition amount of the scale inhibitor is less than 1/10 times the content of the polyvalent inorganic cation in the raw water, the effect of adding the scale inhibitor cannot be sufficiently obtained. Even if the scale inhibitor is added in an excessively large amount, it is not preferable in terms of drug cost. Therefore, it is preferable that the content of the polyvalent inorganic cation in the raw water is 1/10 to 5 times by weight.

  The raw water to which the biodegradable scale inhibitor is added is then adjusted to pH 9.5 or more, preferably 10 or more, more preferably 10.5 to 12, for example, pH 10.5 to 11 by adding an alkali agent. Introduced into the membrane separator 4. The alkaline agent used here is not particularly limited as long as it is an inorganic alkaline agent that can adjust the pH of raw water to 9.5 or higher, such as sodium hydroxide and potassium hydroxide.

  Examples of the RO membrane of the RO membrane separation device 4 include those having alkali resistance, such as a polyetheramide composite membrane, a polyvinyl alcohol composite membrane, an aromatic polyamide membrane, and the like. A low-fouling RO membrane of 95% or more of polyvinyl alcohol is used. This RO membrane may be of any type such as a spiral type, a hollow fiber type, and a tubular type.

  The permeated water of the RO membrane separation device 4 is then reused after adding an acid to adjust the pH to 4 to 8, further subjecting it to activated carbon treatment as necessary. There is no restriction | limiting in particular as an acid used here, Mineral acids, such as hydrochloric acid and a sulfuric acid, are mentioned.

  On the other hand, the concentrated water of the RO membrane separation device 4 is preferably adjusted to pH 5 to 8 by adding an acid, then returned to the biological treatment tank 1 in the previous stage for biological treatment, and then solid-liquid in the coagulation sedimentation tank 2. Separated, a part of the separated water is discharged out of the system, and the remaining part is fed to the tank 3 for RO membrane separation treatment. In addition, there is no restriction | limiting in particular as an acid used for pH adjustment of concentrated water, Mineral acids, such as hydrochloric acid and a sulfuric acid, are mentioned.

  As shown in FIG. 1, by adding a predetermined amount of scale inhibitor to raw water and adjusting the pH to 9.5 or higher and then performing RO membrane separation treatment, long-term reduction in flux in the RO membrane separation device is caused without causing a decrease in flux. It is possible to obtain a high-quality treated water from which TOC is highly removed by performing a stable treatment over a period of time. Further, by biologically treating the RO concentrated water obtained by this RO membrane separation treatment, organic substances including biodegradable scale inhibitors in the concentrated water can be removed by highly biological treatment. At this time, as described above, the scale inhibitor is biodegraded, so that the polyvalent inorganic cation is liberated in the biological treatment system, and this polyvalent inorganic cation is taken into the sludge. By raising, the sedimentation property of the sludge in the latter agglomeration sedimentation tank can be enhanced and the solid-liquid separation property can be improved.

  FIG. 1 shows an example of an embodiment of the present invention, and the present invention is not limited to the illustrated one as long as the gist thereof is not exceeded. In FIG. 1, after adding the scale inhibitor to the raw water, the alkali is added to adjust the pH, but after adding the alkali to the raw water and adjusting the pH, the scale inhibitor may be added. You may perform pH adjustment and the addition of a scale inhibitor simultaneously. Further, the process by the RO membrane separation apparatus is not limited to a single stage process, and may be a multistage process having two or more stages. In addition, in TOC-containing wastewater discharged from electronic device manufacturing factories, there are few cases in which polyvalent inorganic cations such as calcium ions that cause scale are mixed. When an inorganic cation or the like is mixed, a cation exchange tower for removing the polyvalent inorganic cation may be provided prior to the addition of the scale inhibitor, and the polyvalent inorganic cation may be removed in advance. Furthermore, you may provide the mixing tank for pH adjustment and the addition of a scale inhibitor.

  Further, when multistage treatment of two or more stages is performed by the RO membrane separation apparatus, such biological treatment may be performed only for the RO concentrated water of the first stage RO membrane separation apparatus, and the same applies to other RO concentrated water. You may perform processing. However, in the case of the two-stage RO membrane separation treatment, the concentrated water of the second-stage RO membrane separation apparatus is usually returned to the raw water side.

In addition, the biological treatment in this invention will not be specifically limited if a BOD component can be removed from concentrated water, such as an activated sludge method and a biofilm method.
Examples of water to be treated in the present invention include general waste water (discharged water), acid-alkali waste water, fluorine-containing waste water, and organic waste water. Moreover, although there is no restriction | limiting in particular in the TOC density | concentration of raw | natural water, It is especially preferable that it is 1-5 mg / L.

  Hereinafter, the present invention will be described in more detail with reference to Examples, Comparative Examples and Reference Examples.

Example 1
First, water containing a TOC concentration of 10 mg / L and a calcium ion concentration of 100 mg / L as a polyvalent inorganic cation was prepared assuming raw water discharged from an electronic device manufacturing factory, and used as raw water. After adding polyaspartic acid as raw biodegradable scale dispersant to 1/10 times the calcium ion concentration (10 mg / L) to the raw water prepared in this way, NaOH was added to pH 10.5, RO membrane separation treatment was performed with a RO membrane separator (Nitto Denko's low-pressure aromatic polyamide RO membrane “NTR-759”) under conditions of a water flow rate of 75 L / h and a recovery rate of 80%.

The change over time in the rate of decrease of the membrane flux (25 ° C., 1.47 MPa) of the RO membrane separator at this time was examined, and the results are shown in FIG.
Further, after adding HCl to the RO concentrated water obtained by this RO membrane separation treatment to adjust the pH to 8, it was passed through a sponge-filled biological treatment apparatus under conditions of HRT (Hydric Retention Time) for 3 h. Watered. The biological treatment operation was started when the treatment capacity reached a steady state.
The TOC of the biological treatment feed water (concentrated water) supplied to this biological treatment and the TOC of the biological treatment water were examined over time, and the results are shown in Table 1.

Comparative Examples 1 and 2
In Example 1, the raw water was treated in the same manner except that the pH of the RO feed water was 7 (Comparative Example 1) or 5 (Comparative Example 2), and the results are shown in FIG.

Reference examples 1 and 2
In Example 1, the scale inhibitor becomes 1/20 times (5 mg / L) (Reference Example 1) or 1/15 times (6.7 mg / L) (Reference Example 2) of the calcium ion concentration of raw water. The raw water was treated in the same manner except that it was added to, and the results are shown in FIG.

Comparative Example 3
RO membrane separation treatment and biological treatment under the same conditions as in Example 1 except that an EDTA-based scale inhibitor that is hardly biodegradable as a scale dispersant is added so as to be 5 times the calcium ion concentration (500 mg / L). Carried out. The TOC of the biological treatment feed water (concentrated water) supplied to the biological treatment at this time and the TOC of the biological treatment water were examined over time, and the results are shown in Table 1.

The following can be understood from the above results.
<RO membrane separation treatment of raw water>
In Example 1, it was possible to prevent a decrease in membrane flux over a long period of time by adding a scale inhibitor to adjust the pH of the RO water supply. On the other hand, in Comparative Examples 1 and 2, it was revealed that the membrane flux decreased to about 60% of the initial membrane flux in only 20 days from the start of operation. Adsorption of organic substances was observed from the closed film surface. On the other hand, from Reference Examples 1 and 2, as the amount of scale dispersant added increases, the membrane flux decreases more slowly, but the scale dispersant must be added to be 1/10 or more times the calcium ion concentration of the raw water. It was revealed that the membrane surface was blocked. When this closed membrane surface was analyzed, precipitation of CaCO ₃ scale was observed.

<Bio-treatment of RO concentrated water>
In Comparative Example 3 using a non-biodegradable scale dispersant as the scale dispersant, the TOC concentration of biologically treated water could only be reduced by about 20%, while using a biodegradable scale dispersant as the scale dispersant. In Example 1, the TOC concentration of biologically treated water could be reduced by 70% or more, and the effectiveness of the combination of biodegradable scale inhibitor and biological treatment became clear.

  INDUSTRIAL APPLICABILITY The present invention is effectively applied to water treatment for discharging, collecting or reusing wastewater containing high or low concentration TOC discharged in the electronic device manufacturing field, semiconductor manufacturing field, and other various industrial fields.

It is a systematic diagram showing an embodiment of a water treatment device and a water treatment method of the present invention. It is a graph which shows the time-dependent change of the film | membrane flux in Example 1, Comparative Examples 1 and 2, and Reference Examples 1 and 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Biological processing tank 2 Coagulation sedimentation tank 3 Tank 4 RO membrane separator

Claims (12)

A scale inhibitor addition means for adding a biodegradable scale inhibitor that suppresses scaling of the polyvalent inorganic cation to the water to be treated containing the BOD component and the polyvalent inorganic cation;
PH adjusting means for adjusting the pH of the water to be treated to 9.5 or more by adding alkali to the water to be treated before, after or simultaneously with the addition of the scale inhibitor;
Reverse osmosis membrane separation means for separating the treated water that has passed through the scale inhibitor addition means and the pH adjustment means into permeated water and concentrated water;
A water treatment apparatus comprising biological treatment means for treating a BOD component contained in the concentrated water.   The water treatment apparatus according to claim 1, wherein the water to be treated is a part of the treated water of the biological treatment means.   3. The scale inhibitor adding means according to claim 1, wherein the scale inhibitor is added to the water to be treated at least 1/10 times the total amount of polyvalent inorganic cations in the water to be treated. Water treatment equipment.   The reverse osmosis membrane according to any one of claims 1 to 3, wherein the reverse osmosis membrane of the reverse osmosis membrane separator is subjected to a reverse osmosis membrane separation treatment of 1500 mg / L of saline under the conditions of 1.47 MPa, 25 ° C, and pH 7. A water treatment apparatus, which is a polyvinyl alcohol-based low fouling reverse osmosis membrane having a salt rejection of 95% or more.   5. The water treatment apparatus according to claim 1, wherein the pH adjusting unit adjusts the pH of the water to be treated to 10.5 to 12. 12.   6. The water treatment apparatus according to claim 1, further comprising means for adjusting the pH to 5 to 8 by adding an acid to the concentrated water introduced into the biological treatment means. A scale inhibitor addition step of adding a biodegradable scale inhibitor that suppresses scaling of the polyvalent inorganic cation to the water to be treated containing the BOD component and the polyvalent inorganic cation;
A pH adjusting step of adjusting the pH of the water to be treated to 9.5 or more by adding an alkali to the water to be treated before, after or simultaneously with the addition of the scale inhibitor;
A reverse osmosis membrane separation step of supplying water to be treated that has undergone the scale inhibitor addition step and the pH adjustment step to a reverse osmosis membrane separation device and separating it into permeate and concentrated water;
And a biological treatment process for treating the BOD component contained in the concentrated water.   The water treatment method according to claim 7, wherein the water to be treated is a part of the treated water in the biological treatment process.   The scale inhibitor addition step according to claim 7 or 8, characterized in that, in the treated water, a scale inhibitor more than 1/10 times the total polyvalent inorganic cation content in the treated water is added. Water treatment method.   The reverse osmosis membrane according to any one of claims 7 to 9, wherein the reverse osmosis membrane of the reverse osmosis membrane separator is subjected to a reverse osmosis membrane separation treatment of 1500 mg / L of saline under the conditions of 1.47 MPa, 25 ° C, and pH 7. A water treatment method characterized by being a polyvinyl alcohol-based low fouling reverse osmosis membrane having a salt rejection of 95% or more.   11. The water treatment method according to claim 7, wherein the pH adjusting unit adjusts the pH of the water to be treated to 10.5 to 12. 12.   The water treatment method according to any one of claims 7 to 11, further comprising a step of adjusting the pH to 5 to 8 by adding an acid to the concentrated water introduced into the biological treatment step.

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