JP2005279618A - Liquid chemical cleaning method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cleaning method for obtaining a high restoration rate and recycling a membrane module. <P>SOLUTION: In the liquid chemical cleaning method for cleaning the filtration membrane module composed of a hydrophobic resin with an oxalic acid solution, it is cleaned with the liquid mixture of a sodium hypochlorite solution and a sodium hydroxide solution before or after that. Also, the filtration membrane module to be cleaned filters one of ground water, well water, water of rivers and water of lakes and marshes or a liquid mixture thereof. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for cleaning a membrane. More specifically, the present invention relates to a method for cleaning a film made of a hydrophobic resin.

  Membranes that separate components in liquids and remove SS have been used for various applications because of energy saving. For example, factory wastewater treatment, river water and groundwater clarification, seawater desalination, bioreactor, etc. are examples. Various types of membranes have been used depending on the application. For example, river water is filtered through a microfiltration membrane, an ultrafiltration membrane, or a reverse osmosis membrane and used as drinking water. In the drainage, the activated sludge water is separated into activated sludge solids and filtered water by a microfiltration membrane or dynamic filtration.

  There are two types of membranes used for filtration, one made of a hydrophilic resin and one made of a hydrophobic resin.

However, such filtration may cause SS and adsorbate to adhere to the filtration surface and reduce the filtration capacity, and a necessary amount of filtered water may not be obtained. For this reason, by regularly or non-periodically cleaning the filtration surface, the SS component attached to the filtration surface is removed, and the filtration capability is maintained. For example, in JP-A-8-141375, filtration performance is maintained by reversely permeating filtered water from the filtration side periodically. Japanese Patent Laid-Open No. 2001-38177 proposes to perform filtration while cleaning the filtration surface by supplying air from below the filter body. Furthermore, Japanese Patent Laid-Open No. 2002-126470 has proposed a method in which the filter surface cannot be cleaned even by such a method, and the filter body is chemically cleaned.
Still, it takes time and labor to recover the filtration capacity to 100%. Especially when the filtration membrane made of hydrophobic resin is used to filter groundwater, well water, river water, lake water, or a mixture of them, So far, even after chemical cleaning, the recovery rate is low and it is very difficult to reuse.
JP 2002-248325 A JP-A-10-249338

  The present invention provides a method for cleaning a membrane made of a hydrophobic resin.

  The inventor of the present invention has a high recovery rate with respect to a method for washing a filtration membrane when a membrane composed of a hydrophobic resin contains any of groundwater, well water, river water, lake water, or a mixture thereof. This completes the cleaning method that makes it possible to reuse the membrane module.

  The invention according to claim 1 is a chemical cleaning method for cleaning a filtration membrane module with an aqueous oxalic acid solution, which is cleaned with a mixed solution of an aqueous sodium hypochlorite solution and an aqueous sodium hydroxide solution before or after that. This is a chemical cleaning method. The invention of claim 2 is a cleaning method in which the filtration membrane module to be washed contains any of groundwater, well water, river water, lake water, or a membrane module that filters a mixed solution thereof. In the invention of claim 3, the concentration of the cleaning chemical solution is 100 to 30,000 mg / liter for the oxalic acid aqueous solution, and the sodium hypochlorite aqueous solution is 10 to 2,000 ppm in terms of free chlorine concentration. The aqueous solution is a chemical solution cleaning method of 100 to 30,000 mg / liter. The invention according to claim 4 is the chemical solution cleaning method according to any one of claims 1 to 3, wherein the filtration membrane module to be washed is a microfiltration membrane or an ultrafiltration membrane, and the filtration membrane is made of a hydrophobic resin. The invention according to claim 5 is the chemical solution cleaning method according to any one of claims 1 to 4, wherein the filtration membrane is made of a polyether sulfone resin.

  In the present invention, chemical cleaning of the filtration membrane is performed with an aqueous oxalic acid solution. A commercially available oxalic acid can be used. In the present invention, oxalic acid is used and acts on an inorganic substance adhering to the film, and is particularly effective for the PES film as compared with other acids, and a high cleaning effect is obtained.

  Further, before or after washing with oxalic acid, washing is performed with a mixed solution of sodium hypochlorite aqueous solution and sodium hydroxide aqueous solution. When fungi or organic substances are present as film deposits, the cleaning effect is high. Depending on the state of attachment of the deposit (for example, whether it is layered or the like), there are cases where it is more effective to perform before oxalic acid cleaning and cases where it is more effective to perform after that. Sodium hydroxide is considered to dissolve organic substances and the like, and sodium hypochlorite further decomposes it, so it is considered to be highly effective. When sodium hypochlorite is used alone, the rate of consumption is high. Therefore, it is preferable that the sodium hypochlorite is used alone as a mixed solution because the durability of the cleaning effect is low.

  In the cleaning method of the present invention, the type of treated water to be processed is not limited. For example, it can be used for washing a filtration membrane module treated with ground water, well water, river water, lake water, or a mixture thereof.

  As for the concentration of each component in the chemical solution used for cleaning, it is preferable to use the concentration within the following range. The concentration of the oxalic acid aqueous solution is 100 to 30,000 mg / liter, more preferably 1,000 to 10,000 mg / liter. If the oxalic acid concentration is higher than this range, the hollow fiber itself may be damaged. If it is lower than this range, the cleaning effect is low and the practical level is not reached. Or cleaning is long and impractical.

  The concentration of sodium hypochlorite is such that the free chlorine concentration is in the range of 10 to 2,000 ppm, more preferably 500 to 1,000 ppm. If the sodium hypochlorite concentration is higher than this range, the hollow fiber membrane itself may be damaged, and if it is lower than this range, the cleaning effect may not be sufficiently obtained.

  Furthermore, the concentration of sodium hydroxide is 100 to 30,000 mg / liter, more preferably 1,000 to 5,000 mg / liter. If the concentration of sodium hydroxide is higher than this range, the hollow fiber membrane itself may be damaged, and if it is lower than this range, the cleaning effect may not be sufficiently obtained.

  The present invention is particularly effective for chemical cleaning of a filtration membrane containing a hydrophobic resin as a main component. Hydrophobic membranes are difficult to remove dirt adhering to the surface of the membrane, but by using the oxalic acid and a mixture of sodium hypochlorite and sodium hydroxide by the cleaning method of the present invention, this dirt is removed. Can be removed efficiently.

  The method of the present invention can be carried out as follows. First, an oxalic acid aqueous solution having a predetermined effective concentration is prepared. This is placed in, for example, a chemical tank and charged from the permeation side of the filtration membrane module at a predetermined rate using a chemical pump. Then, before or after washing with oxalic acid, washing is performed with a mixed solution of sodium hypochlorite and sodium hydroxide in the same manner as oxalic acid. At this time, sodium hypochlorite is preferably added after being heated to a predetermined temperature.

  The hydrophobic resin that is the material of the membrane of the membrane module used in the present invention refers to polysulfone resin, polyacrylonitrile resin, polyethylene resin, polyethylene terephthalate resin, and fluorine resin. Polyether sulfone resin and polysulfone resin are preferable. Further, the membrane may have any pore diameter. A microfiltration membrane or an ultrafiltration membrane is preferable.

  In the chemical solution cleaning method of the present invention, a membrane module made of a hydrophobic resin can be effectively cleaned, and the performance as a membrane module can be recovered and reused.

  Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

  Hollow fiber membrane module FS10-FUS1582 (manufactured by Daisen Membrane Systems Co., Ltd.) (a hollow fiber membrane made of polyethersulfone resin with an effective membrane area of 5 m2) that was used for filtration of well water for 3 months From the permeate side, an oxalic acid aqueous solution having a concentration of 1.0% and 40 ° C. was charged at a flow rate of 1.5 m 3 / H, and washing by filtration was carried out for 3 hours. Next, a mixed chemical solution of a sodium hypochlorite aqueous solution with a free chlorine concentration of 1000 ppm and a sodium hydroxide aqueous solution with a concentration of 2000 mg / liter is used, and the chemical solution is reversed from the permeate side for 20 seconds at a flow rate of 1.5 m 3 / H. After permeation, the charging was stopped, and the membrane module was immersed and left at 20 ° C. for 15 hours while the chemical solution was filled in the module. Thereafter, the mixed chemical solution was again permeated for 30 minutes at a flow rate of 1.5 m 3 / H, and then flushing washing was performed for 20 minutes and circulation filtration washing was performed for 4 hours. The permeation flux of the membrane module after washing recovered to 95% performance compared to the value immediately after production.

  Hollow fiber membrane module FS10-FUS1582 (manufactured by Daisen Membrane Systems Co., Ltd.) (a hollow fiber membrane made of polyethersulfone resin with an effective membrane area of 5m2) used for groundwater filtration for one year, free chlorine concentration Using a mixed chemical solution of 1000 ppm sodium hypochlorite aqueous solution and 2000 mg / liter sodium hydroxide aqueous solution, it was washed by circulation filtration for 2 hours. Next, while charging an aqueous oxalic acid solution with a concentration of 1.0% and 40 ° C. at 1.5 m 3 / H, washing by filtration was carried out for 2 hours, followed by flushing washing for 20 minutes, and the chemical solution from the permeation side for 20 minutes. Washing was completed by reverse permeation. The permeation flow rate was 36% before washing as compared to the value immediately after production, whereas it recovered to 135% after washing.

  From Examples 1 and 2 described above, a high cleaning effect can be obtained by washing the filtration membrane made of a hydrophobic resin with oxalic acid and a mixed solution of sodium hypochlorite and sodium hydroxide by the method of the present invention. It became clear that

Claims (5)

  A chemical cleaning method for cleaning a filtration membrane module made of a hydrophobic resin with an aqueous oxalic acid solution, wherein the cleaning is performed with a mixed solution of a sodium hypochlorite aqueous solution and a sodium hydroxide aqueous solution before or after that.   2. The chemical solution cleaning method according to claim 1, wherein the filtration membrane module to be washed is a membrane module for filtering any of groundwater, well water, river water, lake water, or a mixture thereof.   The concentration of the oxalic acid aqueous solution during the chemical cleaning is 100 to 30,000 mg / liter, the free chlorine concentration in the sodium hypochlorite aqueous solution is 10 to 2,000 ppm, and the concentration of the sodium hydroxide aqueous solution is The method for cleaning a chemical solution according to claim 1 or 2, wherein the concentration is 100 to 30,000 mg / liter.   The chemical liquid cleaning method according to any one of claims 1 to 3, wherein the filtration membrane module to be washed includes a microfiltration membrane or an ultrafiltration membrane, and the filtration membrane is made of a hydrophobic resin.   The chemical | medical solution washing | cleaning method in any one of Claims 1-4 whose filtration membrane consists of polyether sulfone resin.