JP2005081268A - Treatment method and treatment apparatus for organic substance-containing wastewater - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform a stable treatment over a long term by preventing flux deterioration and biofouling due to organic substances adhering to a membrane surface in an RO (reverse osmosis) membrane separator when treating and recovering wastewater with high or low concentrations of organic substances, discharged from an electronic device manufacturing plant and other various fields by using the RO membrane separator; to obtain a treated water of high quality by efficiently reducing TOC (trace organic compound) concentration in water. <P>SOLUTION: After an alkali is added to the organic substance-containing wastewater to adjust its pH to 9.5 or higher and the wastewater is passed through the first RO membrane separator 2, the alkali is added thereto to adjust pH to 9.5 or higher again and the wastewater is passed through the second RO membrane separator 3. By adjusting the pH of the water supplied to RO to 9.5 or higher, the biofouling in the RO membrane separators 2, 3 is prevented, and nonionic surfactants are prevented from adhering to the membrane surface to prevent the flux deterioration. A TOC value is reduced by performing the two-stage RO membrane separation treatment. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  In the present invention, when wastewater containing high or low concentration organic matter (TOC) discharged from an electronic device manufacturing factory or the like is treated and recovered using a reverse osmosis (RO) membrane separator, organic matter in the RO membrane separator Of organic wastewater containing 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 bio-fouling due to film surface adhesion And a processing 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 an RO membrane separation device, the problem that the membrane surface of the RO membrane is clogged and the flux is reduced 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.

In JP-A-11-128923, an alkali is added to boron-containing water to adjust the pH to 9.2 or higher, followed by RO membrane separation treatment, and alkali is added to the permeated water to adjust the pH to 9.2 or higher. A method for removing boron by performing RO membrane separation is described. However, this method is intended to reduce the boron concentration, and there is no description about the removal of organic substances, and the adjusted pH value actually employed in the examples is 9.2. This is different from the advanced organic matter processing technology of the invention.
JP 2002-336886 A Japanese Patent Laid-Open No. 11-128923

  The present invention solves the above-mentioned conventional problems, and when processing / recovering wastewater containing high or low concentration organic matter discharged from an electronic device manufacturing factory and other various fields using an RO membrane separator, Organic matter that obtains 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 membrane surface adhesion of organic matter in the separator It aims at providing the processing method and processing apparatus of contained wastewater.

  The method for treating organic matter-containing wastewater of the present invention includes a first pH adjustment step of adjusting the pH to 9.5 or more by adding alkali to the organic matter-containing wastewater, and a pH adjustment obtained in the first pH adjustment step. A first membrane separation treatment step for subjecting water to reverse osmosis membrane separation; a second pH adjustment step for adjusting the pH to 9.5 or higher by adding alkali to the permeated water of the first membrane separation treatment step; And a second membrane separation treatment step of performing reverse osmosis membrane separation treatment on the pH adjusted water obtained in the second pH adjustment step.

  The treatment apparatus for organic matter-containing wastewater of the present invention includes a first pH adjusting means for adjusting the pH to 9.5 or more by adding alkali to the organic matter-containing wastewater, and a pH adjustment obtained by the first pH adjusting means. A first reverse osmosis membrane separation device into which water is introduced; a second pH adjusting means for adjusting the pH to 9.5 or more by adding alkali to the permeated water of the first reverse osmosis membrane separation device; And a second reverse osmosis membrane separation device into which pH adjusted water obtained by the second pH adjusting means is introduced.

  In the present invention, the pH of the water to be treated introduced into the first RO membrane separation device (hereinafter sometimes referred to as “first RO water supply”) is adjusted to 9.5 or more to adjust the first stage RO membrane. After passing water through a separation device (hereinafter sometimes referred to as “first RO membrane separation device”), the permeated water of this first RO membrane separation device (hereinafter sometimes referred to as “first RO permeated water”) is alkali. Is added to adjust the pH to 9.5 or higher, and this water is supplied to the second stage RO membrane separator (hereinafter sometimes referred to as “second RO membrane separator”) (hereinafter “second RO water supply”). ).).

  The reason why the pH of the first RO feed water is adjusted to 9.5 or higher is as follows.

  That is, microorganisms cannot live in the alkaline region. Therefore, by adjusting the pH of the RO feed water to 9.5 or more, it becomes possible to create an environment where 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.

  The reason for adjusting the pH of the second RO water supply to 9.5 or higher is as follows.

  That is, the higher the TOC concentration of the water to be treated, the worse the TOC value of the first RO permeated water, and the TOC cannot be ignored when recovering and reusing this permeated water. Therefore, in the present invention, as a means for obtaining treated water with further reduced TOC, the RO membrane separation devices are arranged in two stages in series, and the two-stage RO treatment method is adopted, but the first RO adjusted to pH 9.5 or higher. When the first RO permeated water obtained by treating the feed water with the first RO membrane separation device is passed through the second RO membrane separation device as it is, the second RO membrane separation device is biofouling by microorganisms or a membrane of a nonionic surfactant There is a risk of film surface clogging due to surface adhesion. That is, the pH of the first RO permeate obtained by subjecting the first RO feedwater having a pH of 9.5 or higher to the RO membrane separation treatment is usually about 8.0 to 9.0, and biofouling or a nonionic surfactant membrane Causes surface adhesion. Therefore, for the purpose of suppressing such trouble, it is necessary to adjust the pH of the first RO permeated water to 9.5 or higher again to provide the second RO water supply.

  According to the method and apparatus for treating organic matter-containing wastewater of the present invention, wastewater containing high-concentration or low-concentration organic matter discharged from an electronic device manufacturing factory and other various fields, particularly wastewater containing a nonionic surfactant. When processing / recovering using RO membrane separators, the TOC concentration in the water is reduced at the same time as performing stable treatment over a long period of time by preventing flux reduction and biofouling due to organic membrane adhesion in the RO membrane separator. Can be efficiently reduced to obtain high-quality treated water.

  DESCRIPTION OF EMBODIMENTS Embodiments of a method and apparatus for treating organic matter-containing wastewater according to the present invention will be described in detail below with reference to the drawings.

  FIG. 1 is a system diagram showing an embodiment of the method and apparatus for treating wastewater containing organic matter according to the present invention.

  First, an alkaline agent is added to the raw water (organic matter-containing wastewater) introduced through the tank 1 to adjust the pH to 9.5 or more, preferably 10 or more, more preferably 10.5 or more, for example, pH 10.5 to 11. The first RO membrane separation device 2 is introduced. 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.

  Next, the permeated water of the first RO membrane separation device 2 is adjusted to pH 9.5 or more, preferably 10 or more, more preferably 10.5 or more, for example, pH 10.5 to 11 by adding an alkali agent to the second RO membrane separation. Introduced into the apparatus 3. 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.

  The concentrated water in the first and second RO membrane separation devices 2 and 3 is discharged to the outside of the system after adjusting to pH neutrality by adding acid as necessary.

  As the RO membranes of the first and second RO membrane separation devices 2 and 3, those having alkali resistance, for example, polyetheramide composite membranes, polyvinyl alcohol composite membranes, aromatic polyamide membranes and the like are preferably used. This RO membrane may be of any type such as a spiral type, a hollow fiber type, and a tubular type.

  As shown in FIG. 1, RO membrane separation treatment is performed by adjusting the raw water to pH 9.5 or higher and then performing RO membrane separation treatment, and then adjusting the pH to 9.5 or higher again and performing second-stage RO membrane separation treatment. A high quality treated water from which the TOC is highly removed can be obtained by performing a stable treatment over a long period of time without causing a decrease in the flux at 2 and 3.

  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 of the present invention is not exceeded. For example, the process by the RO membrane separation apparatus is not limited to the two-stage process, and may be a multi-stage process having three or more stages. Moreover, in TOC-containing wastewater discharged from electronic device manufacturing factories, there are few cases where calcium ions, etc., which cause scales are basically mixed, but when raw materials contain calcium ions, RO membranes You may install a softening apparatus in the front | former stage of a separation apparatus. Moreover, you may provide the mixing tank for pH adjustment.

  Hereinafter, the present invention will be described more specifically with reference to examples, comparative examples, and experimental examples.

Example 1
After adding NaOH to the electronic device manufacturing factory waste water (pH 7.2, TOC 10 mg) containing nonionic surfactant as raw water to make the pH 10.5, RO membrane separator (low pressure aromatic polyamide RO membrane manufactured by Nitto Denko) The first stage RO membrane separation treatment was performed under the conditions of “NTR-759”) with a recovery rate of 90%. After adding NaOH to this RO permeate (pH 9.2) and adjusting the pH to 10.5 again, the RO membrane separation device (Nitto Denko ultra-low pressure aromatic polyamide RO membrane “ES-20”) has a recovery rate of 90 The second-stage RO membrane separation treatment was performed under the condition of%.

  Changes over time in the flux of the first stage RO membrane separation apparatus and the viable cell count in the RO concentrated water at this time were examined, and the results are shown in FIGS.

  The TOC value at each point is as shown in Table 1.

Comparative Example 1
The treatment is performed under the same conditions as in Example 1 except that the pH of the first and second RO feed water is set to 7. The time course changes in the membrane flux of the first stage RO membrane separator and the number of viable bacteria in the RO concentrated water are respectively shown. This is shown in FIGS.

Comparative Example 2
The same conditions as in Example 1 except that the pH of the first and second RO feed water was 7, and 5 mg / L of the isothiazoline slime control agent ("Kuriverta EC-503" manufactured by Kurita Kogyo Co., Ltd.) was added to the first RO feed water. FIGS. 2 and 3 show the changes over time in membrane flux and viable cell count of the RO membrane separator.

  As is clear from FIG. 2, in Example 1, no decrease in flux was observed even after the start of water flow for 500 hours, whereas in Comparative Example 1, it was already about half of the initial flux after the start of water flow for 300 hours. Diminished. Moreover, also in the comparative example 2 which added the slime control agent, it fell to about 60% of the initial flux by 300 hours of water flow start.

  From FIG. 3, in Example 1 and Comparative Example 2, no increase in the number of viable bacteria was observed, whereas in Comparative Example 1, the number of viable bacteria increased with an increase in water passage time.

  From the above results, in Comparative Example 1, the flux decreased due to the synergistic effect of the propagation of microorganisms in the RO membrane and the adhesion of the nonionic surfactant to the membrane surface, and in Comparative Example 2, the addition of the slime control agent caused the microbial activity. Even though the propagation can be suppressed, the flux decreases due to the adhesion of the nonionic surfactant to the membrane surface. However, in Example 1 according to the present invention, the propagation of microorganisms in the RO membrane separation apparatus and the nonionic surfactant It is clear that both film surface adhesion can be suppressed simultaneously.

  2 and 3 show the change over time in the flux and viable cell count of the first stage RO membrane separation apparatus, the second stage RO membrane separation apparatus is the same as the first stage RO membrane separation apparatus. In Example 1, which showed almost the same tendency and the pH of the second RO feed water was 10.5, both the growth of microorganisms and the adhesion of the nonionic surfactant to the membrane surface were also observed in the second stage RO membrane separation apparatus. At the same time, the flux did not decrease even after 500 hours from the start of water flow, but in Comparative Examples 1 and 2 in which the pH of the second RO water supply was 7, a decrease in flux with time and an increase in the number of viable bacteria were observed, After 300 hours from the start of water flow, the flux decreased to about 80% of the initial flux.

  Further, as apparent from Table 1, the TOC value that was 0.5 mg / L in the first RO permeated water was reduced to about 0.05 mg / L by the second-stage RO membrane separation treatment, and the second-stage RO membrane It can be seen that the TOC value can be further reduced by performing the separation process.

Experimental example 1
NaOH was added using waste water (pH 7.2, TOC 10 mg) containing electronic device manufacturing factory containing nonionic surfactant as raw water to adjust the pH to 9.5 (No. 1), 9.2 (No. 2), 9 ( No. 3) or 8.5 (No. 4), then RO membrane separation treatment with RO membrane separation device (Nitto Denko low pressure aromatic polyamide RO membrane “NTR-759”) under the condition of 90% recovery rate Went. The change with time of the flux in each RO membrane separation device at this time was examined, and the result is shown in FIG.

  From FIG. 4, it can be seen that by setting the pH of the RO water supply to 9.5 or more, it is possible to suppress non-ionic surfactant membrane surface adhesion and biofouling due to microbial growth, and to suppress a decrease in the flux of the RO membrane separator. . In addition, No. which made RO water supply into pH9.2. From the results of 2, it can be seen that long-term stable treatment of organic matter-containing wastewater is impossible even when the technique disclosed in JP-A-11-128923 is applied.

  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 which shows embodiment of the processing method and processing apparatus of the organic substance containing waste_water | drain of this invention. It is a graph which shows the time-dependent change of the flux of the 1st step | paragraph RO membrane separator in Example 1 and Comparative Examples 1 and 2. FIG. It is a graph which shows a time-dependent change of the viable cell count of the 1st step | paragraph RO membrane separator in Example 1 and Comparative Examples 1 and 2. FIG. 6 is a graph showing a change with time in flux of the RO membrane separation device in Experimental Example 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tank 2 1st RO membrane separation apparatus 3 2nd RO membrane separation apparatus

Claims (4)

A first pH adjusting step of adjusting the pH to 9.5 or higher by adding alkali to the organic matter-containing wastewater;
A first membrane separation treatment step of reverse osmosis membrane separation treatment of the pH adjusted water obtained in the first pH adjustment step;
A second pH adjusting step of adjusting the pH to 9.5 or more by adding an alkali to the permeated water of the first membrane separation treatment step;
A second membrane separation treatment step of reverse osmosis membrane separation treatment of the pH adjusted water obtained in the second pH adjustment step;
An organic matter-containing wastewater treatment method comprising:   In Claim 1, pH is adjusted to 10.5 or more in this 1st pH adjustment process and / or 2nd pH adjustment process, The processing method of the organic substance containing waste_water | drain characterized by the above-mentioned. First pH adjusting means for adjusting pH to 9.5 or higher by adding alkali to organic matter-containing wastewater;
A first reverse osmosis membrane separation device into which pH adjusted water obtained by the first pH adjusting means is introduced;
Second pH adjusting means for adjusting the pH to 9.5 or higher by adding alkali to the permeated water of the first reverse osmosis membrane separation device;
A second reverse osmosis membrane separation device into which the pH adjusted water obtained by the second pH adjusting means is introduced;
An organic matter-containing wastewater treatment apparatus comprising:   4. The organic matter-containing wastewater treatment apparatus according to claim 3, wherein the first pH adjusting means and / or the second pH adjusting means adjusts the pH to 10.5 or more.

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