JP2007196158A - Membrane module washing method for membrane separation for fe-, cr-, and resist-containing water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane washing method for efficiently washing and removing chromium oxide, iron oxide and resist attached to the membrane surface of a membrane module for a membrane separation apparatus for Fe-, Cr- and resist-containing water, and keeping the membrane performance high over a long period of time. <P>SOLUTION: The membrane module washing method for the membrane separation apparatus for Fe-, Cr- and resist-containing water comprises a first washing step for washing the membrane module with NaOH solution, and a second washing step for washing with acid. In the second washing step, the acid solution may be replaced once or twice or more during the step to wash the membrane again with a new acid solution. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to chromium oxide, iron oxide, and resist adhered to the membrane surface of a membrane module of a membrane separation apparatus that processes Fe, Cr, and resist-containing water discharged from manufacturing factories such as liquid crystal displays and plasma displays, and semiconductor factories. The present invention relates to a film cleaning method for efficiently cleaning and removing the film to maintain the film performance high over a long period of time.

  Membrane separation treatment is widely adopted in fields such as various wastewater treatment and water purification treatment. By the way, waste water from manufacturing factories such as liquid crystal displays and plasma displays, semiconductor factories, etc. contains resist components such as resins in addition to metal components such as Fe and Cr, and iron oxide on the film surface. Fouling occurs due to the deposition of chromium oxide and the adhesion of resist components, and the permeation performance of the membrane decreases.

  Therefore, when chromium oxide, iron oxide or the like adheres, the membrane module is washed with an acid such as hydrochloric acid or sulfuric acid. However, since the resist component cannot be easily removed with an acid, there is a problem that the permeation performance of the film cannot be sufficiently recovered. For this reason, a cycle of cleaning with an oxidizing agent sodium hypochlorite solution to oxidize and remove the resist adhering to the film surface, and then removing iron oxide and chromium oxide by cleaning with hydrochloric acid or the like. Was performed once or twice or more.

  Although the membrane performance can be recovered by the combined use of sodium hypochlorite (oxidant) and an acid as described above, hypochlorous acid as an oxidant as a result of subsequent research by the present inventors. It was found that when soda and iron coexist, the membrane material tends to deteriorate due to the catalytic action of iron and chlorine, and the membrane life is shortened.

  The present invention has been made in view of the above-mentioned problems, and efficiently removes chromium oxide, iron oxide and resist adhering to the membrane surface of the membrane module in the membrane separator for Fe, Cr and resist-containing water. Another object of the present invention is to provide a film cleaning method for maintaining high film performance over a long period of time.

  In order to solve the above-described problems, the membrane module cleaning method for membrane separation treatment of Fe, Cr and resist-containing water according to the present invention includes a first cleaning step using an NaOH solution and a second cleaning step using an acid. (Claim 1).

  Iron and chromium are oxidized in water to form oxides and deposit on the film surface, and the resist adheres to the film surface. Among these, the metal oxide does not dissolve in the alkali, but the acid dissolution proceeds rapidly by treating with the NaOH solution and then treating with the acid. On the other hand, the resist component does not dissolve in acid, but dissolves in alkali. Therefore, in the above invention (invention 1), by first removing the resist by washing the membrane module with a NaOH solution and making it into an alkaline region, and then treating with an acid, turning to the acidic region, Dissolve and remove iron and chromium oxides. Since these washings do not use sodium hypochlorite as an oxidant, the membrane does not deteriorate due to the catalytic reaction between iron and chlorine.

  The separation membrane to which the present invention is applied is not particularly limited, and can be used for reverse osmosis membranes and nanofiltration membranes, but particularly for ultrafiltration membranes (UF membranes) and microfiltration membranes (MF membranes). It can be used suitably. The material of the membrane is not particularly limited, but can be suitably used for a fluorine-based membrane such as PTFE (polytetrafluoroethylene).

  In the said invention (invention 1), it is preferable that the density | concentration of the said NaOH solution is 2 mass% or more (invention 2). Thereby, a resist can be removed reliably.

  In the above inventions (Inventions 1 and 2), in the second cleaning step, it is preferable that the acid solution is replaced once or twice or more and the membrane is washed again with a new acid solution (Invention 3). . Thus, in the second cleaning step after the first cleaning step with the NaOH solution, the dissolved metal ions stay when the acid solution is held for a long time, so that the cleaning effect decreases with time. By exchanging the acid solution, the dissolved metal ions diffuse into the new acid solution, preventing the penetration of metal ions into the membrane, improving the cleaning effect, and adhering iron and chromium are sufficient Will be removed.

  In the said invention (Invention 1-3), it is preferable to repeat the said 1st washing | cleaning process and 2nd washing | cleaning process 2 cycles or more (Invention 4). Thus, Fe, Cr, and the resist can be sufficiently removed by repeating the first and second cleaning steps a plurality of times according to the degree of contamination of the film surface and the recovery of the film performance by the cleaning.

  According to the method for cleaning a membrane module for membrane separation treatment of Fe, Cr and resist-containing water according to the present invention, an oxidizing agent such as sodium hypochlorite is not used, which may adversely affect the membrane material. Therefore, the membrane can be efficiently cleaned, and the membrane performance can be maintained high over a long period of time. Moreover, since no oxidizing agent is used, there is an effect that chromium is not likely to be excessively oxidized.

Hereinafter, an embodiment of a method for cleaning a membrane module for membrane separation treatment of Fe, Cr and resist-containing water of the present invention will be described in detail.
The cleaning method according to the present embodiment periodically includes a membrane module that performs membrane separation processing of water containing Fe, Cr, and a resist, for example, a manufacturing factory such as a liquid crystal display or a plasma display, and wastewater from a semiconductor factory, Alternatively, when the membrane separation performance falls below a predetermined value, the membrane is washed with an NaOH solution (first washing step), and then washed with an acid (second washing step).

  In the cleaning with the NaOH solution (first cleaning step), it is preferable to use an aqueous NaOH solution having a concentration of 2% by mass or more as the NaOH solution used for the cleaning. If the concentration of the NaOH aqueous solution is less than 2% by mass, the resist adhering to the film surface may not be sufficiently removed. In particular, in order to obtain a sufficient resist removing effect, it is preferable to use an aqueous NaOH solution having a concentration of 3% by mass or more.

  The cleaning time in the first cleaning step is preferably 0.1 hour to 5 hours, and particularly preferably 0.5 hour to 2 hours. If the cleaning time is less than 0.1 hour, a sufficient resist removal effect may not be obtained. If the cleaning time exceeds 5 hours, no further cleaning effect can be obtained. There is a risk that work efficiency may be reduced due to a long time.

  The cleaning method in the first cleaning step may be an immersion cleaning method in which an NaOH solution is injected and held on the primary side of the membrane module, or from the treated water inlet or the concentrated water outlet of the membrane module. A circulating cleaning method may be employed in which the NaOH solution is introduced into the primary side, and is taken out from the concentrated water outlet or the treated water inlet and circulated.

  After washing with NaOH solution, washing with acid is performed (second washing step). Iron oxide and chromium oxide are not dissolved in alkali but dissolved in acid, but by treating with an acid after treating with NaOH solution as in this embodiment, acid dissolution of iron oxide and chromium oxide proceeds rapidly, Iron oxide and chromium oxide can be dissolved more effectively.

  As the acid used for this acid cleaning, mineral acids such as hydrochloric acid and sulfuric acid can be used, and the concentration thereof is 0.5 to 5% by mass, preferably 1 to 3% by mass, particularly preferably about 2% by mass. .

  In addition, the cleaning time of the second cleaning step using acid may be about 0.1 to 5 hours, particularly 0.5 to 2 hours. If the cleaning time is less than 0.1 hour, there is a possibility that sufficient iron and chromium removal effect may not be obtained. Even if the cleaning time exceeds 5 hours, no further cleaning effect can be obtained, As a whole, the work efficiency may be reduced due to a long time.

  In the second cleaning step, it is preferable to replace the acid solution once or twice or more and clean the membrane again with a new acid solution. By exchanging the acid solution, the dissolved metal ions diffuse into the new acid solution, preventing the metal ions from penetrating into the membrane and improving the cleaning effect.

  The replacement of the acid solution may be performed so that the cleaning time of the second cleaning step is evenly distributed. For example, the entire cleaning time of the second cleaning step is 1 hour, and the acid solution is changed once. In the case of replacement, the replacement may be performed once after 30 minutes from the start of cleaning in the second cleaning step. The acid solution may be replaced two or more times. However, even if the replacement frequency is increased too much, not only the cleaning effect corresponding to the replacement frequency is increased, but also the cost is increased. It is desirable to wash about a minute.

  This acid solution cleaning method may be either the immersion cleaning method or the circulation cleaning method in the first cleaning step described above. After the acid cleaning, if necessary, finish cleaning with treated water, raw water, tap water, industrial water, etc. and then restart the operation.

  The cleaning pattern of this embodiment as described above is as shown in FIG. In FIG. 1, “NaOH cleaning” means cleaning with an aqueous NaOH solution, and “acid exchange” means exchanging the acid solution for a new one. Basically, acid cleaning may be performed after NaOH cleaning as shown in FIG. 1 (1). However, as shown in (2), the acid solution is replaced with a new one in the middle of acid cleaning, and acid cleaning is performed. It is preferable to carry out a plurality of times (twice) continuously. In particular, when the membrane surface is very dirty and the permeated water recovery is low, the cycle of (2) can be repeated twice or three times or more as shown in (3).

  In the above embodiment, in the middle of the acid or alkali cleaning step, the cleaning is temporarily suspended and the city water is passed, the amount of permeated water and the membrane permeation differential pressure are measured, and the recovery of the membrane performance is checked. In addition, it may be determined whether or not the acid cleaning liquid needs to be replaced and the replacement timing.

[Example 1]
For the purpose of removing these from waste water containing iron, chromium and resist, in a system in which membrane separation processing is performed with a membrane separation apparatus using an MF membrane manufactured by Nitto Denko Corporation as a membrane module, membranes are formed by membrane fouling. When the permeated water amount of the new membrane (7 m ³ / hr at 0.1 MPa) reached 1.8 m ³ / hr, first, it was washed with a 3% by mass NaOH aqueous solution for 1 hour (first washing Step), followed by washing with a 2.5% by mass HCl solution every 30 minutes, replacing the HCl solution for 1 hour (second washing step). When the first washing step and the second washing step were repeated twice, the permeated water amount was greatly recovered.

[Comparative Example 1]
For the purpose of removing these from waste water containing iron, chromium and resist, in a system in which membrane separation processing is performed with a membrane separation apparatus using an MF membrane manufactured by Nitto Denko Corporation as a membrane module, membranes are formed by membrane fouling. (Permeated water amount in new membrane: 7 m ³ / hr at 0.1 MPa) When the permeated water amount reached 2.8 m ³ / hr, first, washing was performed with a 0.5 mass% NaClO aqueous solution for 50 minutes, and then Washing was performed for 50 minutes with a 2.5 mass% HCl solution. Thereafter, the plate was further washed with a 0.5 mass% NaClO aqueous solution for 50 minutes, and the HCl solution was replaced with an HCl solution every 50 minutes and washed for 100 minutes.

  In the cleaning methods of these Example 1 and Comparative Example 1, the relationship between the cleaning time and the amount of permeated water of the membrane is as shown in FIG. 2, and according to the method of the present invention, without using hypochlorous acid, It was confirmed that a cleaning effect equivalent to or higher than the conventional method (cleaning method using hypochlorous acid) was obtained.

  Moreover, when the membrane module of Example 1 and Comparative Example 1 described above was washed 180 times, in the cleaning method of Example 1, the amount of permeated water recovered without any abnormality in the membrane module itself, but the Comparative Example In the cleaning method 1, the binder (nonwoven fabric layer, made of PP + PE) for bonding the skin layer (made of PTFE) and the support layer (made of PP) of the membrane module was deteriorated, and the skin layer and the support layer were separated. From this, it was confirmed that there was little deterioration of the film according to the method of the present invention. This is probably because sodium hypochlorite is not used for cleaning the membrane module.

It is process drawing which shows the washing | cleaning method of the membrane module of this invention. It is a graph which shows the effect of the membrane cleaning by the cleaning method of the membrane module of Example 1 and Comparative Example 1.

Claims (4)

A first washing step with NaOH solution;
A method for cleaning a membrane module for membrane separation treatment of Fe, Cr and resist-containing water, comprising a second cleaning step using an acid.   The concentration method of the said NaOH solution is 2 mass% or more, The washing | cleaning method of the membrane module for the membrane separation process of Fe, Cr, and a resist containing water of Claim 1 characterized by the above-mentioned.   3. The Fe, Cr, and resist-containing water according to claim 1, wherein in the second cleaning step, the acid solution is replaced once or twice in the middle, and the film is cleaned again with a new acid solution. Method for cleaning membrane module for membrane separation treatment. The said 1st washing | cleaning process and the 2nd washing | cleaning process are repeated 2 cycles or more, The washing | cleaning of the membrane module for the film separation process of Fe, Cr, and a resist containing water in any one of Claims 1-3 characterized by the above-mentioned. Method.

Images