JP2017227575A - Bio-fouling evaluation method of organic separation membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of grasping easily and surely an organic substance causing bio-fouling of a membrane.SOLUTION: A membrane surface in which bio-fouling is confirmed is measured by direct fluorography, and a three-dimensional fluorescence spectrum is compared with that in the state where an organic substance does not adhere thereto, to thereby enable confirmation of existence/absence of a spectrum characteristic to an adhering organic substance. A progress state of adhesion of an organic substance can be confirmed by comparing conditions before and after the use, and a cleaning effect can be confirmed by comparing conditions before and after chemical cleaning of the membrane in which adhesion of an organic substance is confirmed.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a method for evaluating organic substances adhering to an organic separation membrane, and more particularly, to a method for evaluating the state of clogging (hereinafter referred to as biofouling) due to microorganisms or contaminants generated by microorganisms and the regeneration state by chemical cleaning. .

  Water treatment using a separation membrane such as a reverse osmosis membrane (RO membrane) is a technique used in the industrial fields of seawater desalination, pure water production, water supply, and pharmaceutical production water. RO membranes separate ions and molecules and allow water to permeate. In separation using RO membranes, solutes are blocked on the membrane surface, and the raw water for treatment is gradually concentrated, so if a certain substance exceeds the solubility on the primary side, it will precipitate in the form of crystals on the membrane surface. To do. Also, microorganisms propagate on the membrane surface, and so-called biofouling occurs in which the main body and metabolites of the microorganisms block the flow path and obstruct water flow. In addition, RO membranes are also used in recently used water recovery systems. When the total organic matter concentration (TOC) of recovered treated water is high, low-cost biological treatment is used, and many methods are used to reduce TOC. Metabolites are produced from microorganisms by biological treatment after biological treatment. Metabolites can cause RO membrane occlusion.

  When the RO membrane permeate flow rate or water quality deteriorates, cleaning is required, and in order to determine what kind of chemicals will be used to recover the performance, analysis of membrane surface deposits Is important. In addition, the cleaning effect is reduced as the membrane surface is further blocked, and the recovery of the RO membrane is worsened. By performing cleaning with the optimal chemicals, stable operation becomes possible, and it is also important to select cleaning chemicals in advance.

  Conventionally, several RO membranes used in the field are extracted, taken back to the analysis room, and the deposit analysis is performed. The RO membrane used in water treatment is a spiral element, and two flat membranes are cylindrical with a spacer interposed therebetween. The treated water is passed from the inlet side, and the treated water flows into the central water collecting pipe. An analysis flow of the RO membrane is shown in FIG. First, the appearance of the element is observed (101) to confirm the presence or absence of physical destruction. Subsequently, salt water or the like is passed before dismantling, and the amount of water passed at the time of shipment is compared (102). Thereafter, the element is disassembled (103), and the foreign matter adhesion state on the film surface is confirmed (104). When the film surface deposits can be easily sampled (A), the deposits are observed with a microscope (105), composition analysis 1 (106) by fluorescent X-ray or thermal analysis, organic matter analysis 1 (FTIR or Raman spectroscopic analysis 1) ( 107). On the other hand, when the sample cannot be easily sampled or the amount of deposits is small (B), the film surface is directly analyzed. As for the analysis of the film surface, composition analysis (108) of the film surface and organic matter analysis 2 (109) of the film surface are performed.

  In the case of a sampleable substance, it is important to make a comprehensive judgment from the results of microscopic observation and instrumental analysis. Semi-quantitative analysis is performed on the dried deposit by fluorescent X-ray analysis. Thermal analysis is used to judge organic and inorganic carbon components, as in JIS K0102 and sewage treatment test methods. Further, as described above, when the amount of deposits on the film surface is small or when it is desired to check the state of the minute amount of the deposits on the film surface, a qualitative analysis is performed with an EDX analyzer attached to the electron microscope.

In addition to the use of pure water that uses industrial water as treated water, RO membranes are increasingly used as recovered water, and fouling due to organic matter is an important factor in RO membrane performance. It becomes a factor causing the decrease.
For identification of organic substances, a Fourier transform infrared spectrophotometer (hereinafter referred to as FTIR) or Raman spectroscopy is generally used. As FTIR, there is a method in which a film surface is directly measured by a microscopic ATR reflection method, or a collected deposit is measured by a KBr transmission method. If the deposit contains a lot of microorganisms, only a broad peak can be obtained in the infrared absorption spectrum except for the film substrate. Therefore, comprehensive judgment is made based on the results of microscopic observation, elemental analysis using fluorescent X-rays, and FTIR analysis. I do.

  After identifying the deposit, clean it with chemicals appropriate for the deposit. In the case of a metal oxide, cleaning is performed with an inorganic acid, and in the case of an organic substance causing biofouling, cleaning is performed with an alkali cleaning agent such as sodium hypochlorite or sodium hydroxide, or a surfactant. Since chemical cleaning may be performed locally, it is important to confirm the effect of chemical cleaning in advance.

  Also, a method for measuring the membrane fouling substance concentration in the concentrated water from the membrane separator is known in order to avoid a decrease in the permeation flux of the separation membrane in advance (Patent Document 1). In this method, the concentration of the membrane fouling substance, particularly the alkylphenyl ether type nonionic surfactant, is determined from the sample calibration curve from the fluorescence intensity of the concentrated water.

JP 2008-194560 A

“Direct analysis of fluorescence characteristics of natural water corrosive substances using a three-dimensional spectrofluorometer”, Analytical Chemistry Vol. 46, no. 5 (1997)

As a method for confirming the cleaning effect, there is a method for confirming the cleaning effect by elemental analysis of the membrane surface by fluorescent X-ray analysis in addition to a method for confirming the recovery of the permeated water amount by passing water through the cleaned membrane. RO membranes are often composed of a polysulfone substrate and an organic membrane such as a polyamide or cellulose acetate layer. In fluorescent X-ray analysis, the RO membrane itself is composed of carbon derived from organic matter that becomes biofouling. It is detected as carbon without distinction, and it is difficult to confirm the cleaning effect. In addition, organic elements peculiar to organic matter such as phosphorus and nitrogen are difficult to analyze by fluorescent X-ray analysis because they are trace amounts.
The measurement of the concentrated solution as in Patent Document 1 cannot be applied to confirm the state of biofouling.
As described above, grasping the organic matter causing biofouling is important for the regeneration of the RO membrane and the like, and a method for grasping simply and reliably is required.

The present invention provides a method for easily and reliably grasping the contamination state of the separation membrane surface using an organic material such as an RO membrane. That is, this invention has the following aspects.
(1) A method for evaluating the state of organic matter adhesion on the surface of an organic separation membrane by measuring the three-dimensional spectrum of the membrane surface with a fluorometer and comparing the three-dimensional spectrum before and after use of the organic separation membrane A method for evaluating the adhesion of organic substances on the film surface.
(2) A method of removing organic substances adhering to the surface of the organic separation membrane by chemical cleaning, measuring a three-dimensional spectrum of the membrane surface with a fluorometer, and three-dimensional before and after cleaning the organic separation membrane A method comprising confirming the effect of chemical cleaning by comparing spectra.

According to one aspect of the present invention, the state of biofouling on the surface of the organic separation membrane can be easily and accurately confirmed.
Moreover, according to one aspect of the present invention, it is possible to select a cleaning chemical suitable for contamination of the organic separation membrane and to confirm the cleaning effect.

RO membrane analysis flow diagram. RO membrane chemical cleaning flowchart. The three-dimensional fluorescence spectrum figure of a new RO membrane surface. The three-dimensional fluorescence spectrum figure of the RO membrane surface by which biofouling was confirmed. The three-dimensional fluorescence spectrum figure of MF film | membrane surface. The three-dimensional fluorescence spectrum figure of NF film | membrane surface. The three-dimensional fluorescence spectrum figure of RO membrane after alkali washing. The two-dimensional fluorescence spectrum figure of excitation wavelength 280nm by the difference in the washing | cleaning method.

  Organic separation membranes subject to the present invention include organic materials such as reverse osmosis membranes (RO membranes), microfiltration membranes (MF membranes), nanofiltration membranes (NF membranes), and ultrafiltration membranes (UF membranes). The separation membrane used is mentioned. In particular, the present invention is directed to a spiral element in which two flat membranes are wound into a cylindrical shape with a spacer interposed therebetween.

Hereinafter, although an embodiment of the present invention will be described mainly using an RO membrane as a representative example, the present invention is not limited to this and can be applied to other separation membranes.
In the actual equipment, multiple RO membranes are used, and chemical cleaning is carried out locally. In order to carry out effective cleaning in the field, several samples are extracted, and after dismantling, qualitative analysis of deposits is performed, and after cleaning with chemicals, the cleaning effect is confirmed. It is possible to ensure a stable amount of treated water by regularly performing chemical cleaning on site before the RO membrane is blocked. In this evaluation method, the presence or absence of biofouling and the progress status can be confirmed by measuring the membrane surface directly by fluorometry, and the degree of recovery of membrane performance after chemical cleaning can also be evaluated. . In the wastewater recovery system, a slime control agent is used for the purpose of preventing the occurrence of biofouling on the membrane surface, but this is an effective technique as an evaluation method for confirming the effect of the slime control agent.

In FIG. 1, when it is difficult to collect deposits from the film surface (B), in the organic matter analysis 2 (109), the film surface is directly measured by a fluorometric method. Also, when the deposit is collected from the film surface (A), the accuracy of the evaluation is improved by performing the measurement of the film surface by the fluorometric method.
When the film surface is measured by a fluorometric method, a sample film of a predetermined size is cut out from the disassembled flat film, and a cell is produced by sandwiching it with a quartz plate, and the fluorescence is measured with a fluorometer. As the fluorometer, an apparatus capable of measuring a three-dimensional fluorescence spectrum showing fluorescence by various excitation wavelengths is used. In particular, in the present invention, attention is focused on a fluorescence wavelength spectrum of 300 to 400 nm in an excitation wavelength range of 250 to 300 nm. The fluorescence spectrum in this wavelength range is a fluorescence spectrum of organic substances peculiar to biofouling such as proteins and amino acids. In the environmental field, fluorometric evaluation has been carried out as a qualitative method for organic substances in aqueous solution, and the fluorescence peaks appearing in this wavelength range are derived from proteins and amino acids (Reference: “Three-dimensional spectrofluorimetry) Method for Direct Analysis of Fluorescence Properties of Natural Water Corrosive Substances by Meter ”, Analytical Chemistry Vol. 46, No. 5 (1997)). Polysulfonic acid, polyamide, cellulose acetate, etc. constituting the RO membrane show a spectral peak in the wavelength region of 350 to 400 nm in the wavelength range of excitation wavelength of 300 to 360 nm.
In direct measurement of the film surface with a fluorometer, it is preferable to appropriately adjust the slit width, the photomultiplier voltage, and the like on the excitation side and the fluorescence side in order to ensure the presence of a small amount of organic matter attached to the film surface. For example, the slit width is made narrower than that during liquid measurement, or the photovoltage is increased.

The occurrence of biofouling can be confirmed by comparing the fluorescence spectra of the membrane surfaces of the RO membrane before use (new) and the RO membrane after use. Moreover, the effect of chemical cleaning can be confirmed by checking the fluorescence spectrum before and after chemical cleaning.
FIG. 2 shows a flow of cleaning confirmation after the identification of deposits. In the conventional method, confirmation by qualitative analysis by fluorescent X-ray analysis is performed. However, it is possible to directly confirm the cleaning effect on biofouling by performing evaluation by the fluorometric method.
In FIG. 2, after identifying the deposit, first, the film surface before cleaning is measured (201) by a fluorometric method. Next, chemical cleaning with a flat membrane (202) is performed. After the chemical cleaning, the flat membrane water passing test (203) and the membrane surface after the cleaning are measured by a fluorometric method (204). For chemical cleaning with flat membranes, optimum cleaning conditions are obtained by changing the cleaning conditions such as cleaning time and type of chemicals in various ways. After the effect of chemical cleaning is confirmed, actual cleaning (205) is performed on the spiral element of the actual machine.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited only to these Examples.

Example 1
The analysis conditions by the fluorescence photometry were performed under the following conditions.
Measuring instrument: Spectrofluorometer F-7000 (manufactured by Hitachi)
Measurement conditions: excitation start wavelength 200 nm
Excitation end wavelength 600nm
Fluorescence start wavelength 200nm
Fluorescence end wavelength 600nm
Scanning speed 60000nm / min
Excitation side slit 5.0nm
Fluorescent side slit 5.0nm
Photomultiplier voltage 400V

The RO membrane was disassembled in accordance with the flow shown in FIG. FIG. 3 shows the three-dimensional fluorescence spectrum of the RO membrane surface before use (new), and FIG. 4 shows the three-dimensional fluorescence spectrum of the RO membrane where biofouling has been confirmed. In the three-dimensional spectrum of FIG. 4, a fluorescence peak not shown in FIG. 3 is seen near the excitation wavelength of 280 nm and the fluorescence wavelength of 330 nm.
Analysis of the membrane in the early stage of biofouling is difficult because there are few deposits. For example, when the analysis is performed by FTIR, the film surface is directly measured by the microscopic ATR reflection method or the like, but since the information on the film substrate is obtained as a result, biofouling cannot be identified. In the fluorometric method used in the present invention, as shown in FIG. 4, since the peak of adhering matter (dotted line) can be confirmed in addition to the peak of the film substrate (solid line), it is effective for analysis of a small amount of organic adhering matter. It was confirmed.

FIG. 5 shows the three-dimensional fluorescence spectrum of the MF film and FIG. 6 shows the NF film. In many cases, MF film deposits cannot be collected, and an evaluation method using a fluorometric method is particularly effective.
The MF membrane has a separation pore size of 0.01 μm to 10 μm and is mainly intended for removal of microorganisms and fine particles in the liquid. The NF membrane is a large organic membrane such as ions (divalent ions) or saccharides having a large hydration radius. Is a membrane used in a water treatment system in the same manner as an RO membrane.
In FIGS. 4-6, the spectrum of the fluorescence wavelength of 300-400 nm was seen in the wavelength range of excitation wavelength 250-300 nm, and presence of the organic substance used as biofouling was confirmed.

(Example 2)
FIG. 7 shows the three-dimensional fluorescence spectrum of the membrane surface after the alkali-washed RO membrane with biofouling is washed with sodium hydroxide. It can be seen that the peaks near the excitation wavelength of 280 nm and the fluorescence wavelength of 330 nm detected in FIG. The effect of the chemical cleaning can be confirmed by the change in the amount of permeated water of the RO membrane after the cleaning and the evaluation method by the fluorescence photometry. FIG. 8 shows a comparison of two-dimensional spectra at an excitation wavelength of 280 nm of a film before cleaning, a film after pure water cleaning, and a film after alkali cleaning. When the permeated water amount of a new membrane is 1, the permeated water amount of the membrane before cleaning is 0.6, the permeated water amount after pure water cleaning is 0.7, and the permeated water amount after alkali cleaning is 0.9. Recovers. The comparison of the fluorescence intensities was performed by standardizing the fluorescence intensities near the excitation wavelength of 320 nm and the fluorescence wavelength of 370 nm, which are the fluorescence peaks of the film, as 1. From the result of FIG. 8, it can be confirmed that the cleaning effect of the alkali cleaning is higher than that of the pure water cleaning as in the recovery of the permeated water amount.
The effectiveness of the slime control agent as well as the chemical cleaning effect on the bio-fouled RO membrane surface can be confirmed by evaluation using a fluorometric method.

DESCRIPTION OF SYMBOLS 101 Appearance observation 102 Water flow test 103 Dismantling 104 Deposit collection 105 Microscopic observation 106 Composition analysis 1
107 Organic matter analysis 1
108 Composition analysis of membrane surface 109 Organic matter analysis 2

Claims (6)

  A method for evaluating the state of organic matter adhesion on the surface of an organic separation membrane, measuring a three-dimensional spectrum of the membrane surface with a fluorometer, and comparing the three-dimensional spectrum before and after use of the organic separation membrane, A method to evaluate the adhesion of organic matter on the surface.   The method according to claim 1, wherein the organic substance is identified by the presence or absence of a spectrum having a fluorescence wavelength of 300 to 400 nm in a wavelength range of excitation wavelength of 250 to 300 nm.   The organic separation membrane is a spiral element obtained by winding a flat membrane, and after disassembling the spiral element, the sample membrane surface cut out from the flat membrane is measured with a fluorometer. 2. The method according to 2.   A method for removing organic substances adhering to the surface of an organic separation membrane by chemical cleaning, measuring the three-dimensional spectrum of the membrane surface with a fluorimeter, and comparing the three-dimensional spectrum before and after cleaning the organic separation membrane And confirming the effect of chemical cleaning by   The method according to claim 4, wherein the organic substance is confirmed by the presence or absence of a spectrum having a fluorescence wavelength of 300 to 400 nm in a wavelength range of excitation wavelength of 250 to 300 nm.   The organic separation membrane is a spiral type element obtained by winding a flat membrane, and after disassembling the spiral type element, the cleaning effect is confirmed using a sample membrane cut out from the flat membrane, and the obtained results are obtained. The method according to claim 4 or 5, which is applied to cleaning of a spiral element of a real machine.

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