JP2011218267A - Water processing method and water processing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a reverse osmosis membrane from contaminating with microbes in a water processing device using the reverse osmosis membrane.SOLUTION: The water processing device consists of a reverse osmosis membrane module, and a supply pump for supplying processed water to the module and/or a high-pressure pump. A column in which a contact material for removing phosphorus in water is filled is disposed upstream of the supply pump and by passing an entire amount of processed water through the phosphorus removing column, the concentration of phosphorus in the processed water is reduced and phosphorus is supplied to the reverse osmosis membrane.

Description

  The present invention relates to a method and an apparatus for obtaining fresh water from sewage wastewater, industrial wastewater, irrigation water such as rivers and lakes, or seawater using a reverse osmosis membrane. The present invention relates to a water treatment method and apparatus characterized by means for preventing.

  Fresh water production by the reverse osmosis membrane method is used in the field of obtaining fresh water for beverages or industrial use because it can separate and remove salt and toxic substances without phase change, is easy to manage and is energy efficient. ing.

  In general, in water treatment using a reverse osmosis membrane, bacteria, algae, molds, etc. present in the treated raw water or air adhere to the surface of the reverse osmosis membrane, and these abnormally reproduce under certain conditions. As a result, the surface of the reverse osmosis membrane and the flow path of the supply water may be blocked, and there is a risk that the performance of the reverse osmosis membrane will deteriorate and deformation due to an increase in the pressure loss of the flow path may occur. For this reason, methods such as biological treatment, sand filtration, coagulation sedimentation, pressurized flotation, microfiltration or ultrafiltration membranes are usually used before supplying sewage, factory effluent, brine or seawater to the reverse osmosis membrane. In order to prevent the contamination of the reverse osmosis membrane surface by microorganisms, the reverse osmosis membrane surface is sterilized and washed regularly or periodically.

  As a method of sterilizing the reverse osmosis membrane surface, as shown in FIG. 3, a sterilizing agent injection device 10 is provided in the water to be treated of the reverse osmosis membrane, and sodium bisulfite, sulfuric acid, a special sterilizing agent, etc. are injected during operation. In addition to the method of sterilizing the membrane, there is a periodic cleaning in which the desalination apparatus is stopped after a certain period of operation and acid cleaning with citric acid and alkali cleaning with caustic soda are performed.

  In membrane sterilization, a sterilization method for intermittently supplying an acid such as sulfuric acid has been developed (Patent Document 1) and has been put into practical use in many plants. However, this intermittent sterilization can sterilize and remove microorganisms adhering to the membrane surface temporarily, but resistance bacteria are generated by carrying out for a long period of time. It was difficult to prevent.

For sterilization with chemicals other than acids, chlorine (sodium hypochlorite) is generally known as the cheapest and most powerful disinfectant, but for polyamide-based reverse osmosis membranes, It cannot be used because it causes oxidative degradation. For this reason, isothiazoline and recently 2,2-dibromo-3-nitrilopropionamide (DBNPA) are attracting attention as non-oxidizing bactericides that do not degrade the reverse osmosis membrane (Patent Document 2, Non-Patent Document 1). ). However, since isothiazoline and DBNPA are expensive and toxic to the human body, there is a problem that they cannot be used for reverse osmosis membrane sterilization for drinking water production. In addition to these, monochloramine (NH ₂ Cl), chlorine dioxide (ClO ₂ ) and the like, which have weak oxidizing power, have been studied (Non-Patent Document 2), both of which have a low bactericidal effect and toxicity. There are some problems and it has not been widely used.

  For periodic membrane cleaning, once contamination of the membrane surface by microorganisms has progressed, deposits of microorganisms and their metabolites on the membrane surface of the reverse osmosis membrane and the surface of the channel material ( Biofilm) adheres firmly, and it is difficult to completely clean and remove even after repeated washing with acid or alkali.

  In addition to the above-mentioned methods using sterilization and membrane cleaning, reverse osmosis after advanced treatment using ultrafiltration membrane (UF) capable of removing bacteria in pretreatment in recent years. The so-called Integrated Membrane System (IMS), which performs treatment with membranes, has been adopted (Non-Patent Document 1), but even when such advanced pretreatment is performed, the reverse osmosis membrane in the latter stage is caused by microorganisms. The actual situation is that the contamination cannot be completely prevented.

On the other hand, paying attention to the relationship between phosphorus concentration in raw water and biofouling, a method to prevent biofouling by removing phosphorus was developed, adding a flocculant into the activated sludge tank, aggregating phosphorus, agglomeration tank There has been proposed a method (Patent Document 3) for filtering and removing with a membrane filtration device installed inside. Phosphorus in water often exists in the form of phosphate ions (PO ₄ ³⁻ , HPO ₄ ²⁻ or H ₂ PO ₄ ⁻ ), and these are polyphosphoric acids such as deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Since it is incorporated into the body of microorganisms as acid ester chains and adenosine triphosphate (ATP) essential for energy metabolism in the body, it has become one of the essential nutrients essential for biological activities such as growth and growth of microorganisms. By removing this phosphorus, biofouling is to be prevented. However, in the method using coagulation filtration, since only aggregated phosphorus can be excluded, the phosphorus component cannot be sufficiently removed.

  As described above, in a wide range of applications and water treatment apparatuses, it has been difficult to effectively prevent and suppress the contamination of reverse osmosis membranes by microorganisms.

JP 2000-237555 A JP 2006-89402 A JP 2006-15236 A

J. et al. van Agtmaal, H.M. Huitting, P.M. A. de Books, L. L. M.M. J. et al. Paping, Desalination 205 (2007) 26-37 Dooil Kim, Seunghoon Jung, Jinsik Son, Hyungsoo Kim, Seokheon Lee, Desalination 238 (2009) 43-52

  It is an object of the present invention to effectively prevent microbial contamination of a reverse osmosis membrane for a long period of time in a method and apparatus for obtaining fresh water from sewage wastewater, industrial wastewater, river water, lakes and other brackish water, or seawater using a reverse osmosis membrane. It is to provide means for preventing.

  The present invention for solving the above problems is specified by the following features.

(1) Using a reverse osmosis membrane, supplying the treated water to the reverse osmosis membrane and separating the permeated water and the concentrated water by adsorption separation or precipitation separation of the phosphorus component in the treated water Water treatment method.
(2) The water treatment method according to (1), wherein a fungicide is injected after removing the phosphorus component in the water to be treated.

(3) In a water treatment apparatus comprising a reverse osmosis membrane module unit having a reverse osmosis membrane that separates permeate and concentrated water, and a high pressure pump that supplies treated water to the reverse osmosis membrane module unit, on the upstream side of the high pressure pump A water treatment apparatus comprising means for adsorbing and separating or separating and separating phosphorus components contained in water to be treated.
(4) The water treatment apparatus according to (3), further comprising means for injecting a reverse osmosis membrane disinfectant downstream of the means for adsorption separation or precipitation separation of the phosphorus component.

  According to the present invention, the growth of microorganisms on the reverse osmosis membrane surface can be suppressed by removing phosphorus or phosphate ions present in raw water without using a sterilization method using a sterilizer as described above. Can do.

  In the present invention, by removing phosphorus, which is an essential nutrient, from the water to be treated using a contact material, an oligotrophic state for microorganisms can be created, and its growth can be effectively suppressed.

It is a flowchart which concerns on the Example which shows the water treatment method or apparatus of this invention. It is a flowchart which concerns on another Example which shows the water treatment method or apparatus of this invention. It is a flowchart which concerns on the comparative example which shows the water treatment method or apparatus of the conventional method.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  The water treatment method or apparatus of the present invention uses a reverse osmosis membrane to obtain fresh water from sewage wastewater, industrial wastewater, brine such as rivers and lakes, or seawater. Here, the reverse osmosis membrane is a semipermeable membrane that blocks, for example, ions or nonionic substances in the water to be treated and mainly transmits water as a solvent, and a nanofiltration (NF) membrane is also used. In the present invention, it is included in the reverse osmosis membrane. The material and type of the reverse osmosis membrane of the present invention are not particularly limited, but polymer materials such as cellulose acetate polymer, polyamide, polyester, polyimide, and vinyl polymer can be appropriately used.

  The reverse osmosis membrane is usually provided in the form of a reverse osmosis membrane element in which a plurality of reverse osmosis membranes, a feed water flow path material, and a permeate flow path material are alternately stacked to form a spiral shape. It does not depend on the form of the membrane element.

  In addition, the reverse osmosis membrane element is usually a single or a plurality of reverse osmosis membrane modules loaded in series in a pressure vessel to form a reverse osmosis membrane module. Further, the reverse osmosis membrane module is connected to a single or a plurality of parallel or serially. Although configured as a reverse osmosis membrane module unit 7, in the present invention, the configuration of these reverse osmosis membrane elements and modules is not affected.

  In the water treatment apparatus of the present invention, a pressure pump 6 is disposed on the upstream side in order to supply treated water to the reverse osmosis membrane module unit 7. There are various types of pumps, for example, centrifugal pumps, centrifugal pumps, plunger pumps, diaphragm pumps, etc. In the present invention, the types of pumps and their materials are not particularly limited. It is preferable to use one that is suitable for the quality and flow rate of treated water, the required pressure, and the like.

Next, phosphorus removal, which is a feature of the present invention, will be described. In general, phosphorus in water often exists in the form of phosphate ions (PO ₄ ³⁻ , HPO ₄ ²⁻ or H ₂ PO ₄ ⁻ ), which are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). It is incorporated into the body of microorganisms as a polyphosphate ester chain and adenosine triphosphate (ATP), which is indispensable for energy metabolism in the body, and is one of the essential nutrients indispensable for biological activities such as growth and growth of microorganisms.

Here, the phosphorus component in the present invention refers to a component present in water in the form of phosphate ions (PO ₄ ³⁻ , HPO ₄ ²⁻ or H ₂ PO ₄ ⁻ ). These are incorporated into the body of microorganisms as deoxyribonucleic acid (DNA), polyphosphate ester chains of ribonucleic acid (RNA), and adenosine triphosphate (ATP), which is indispensable for biological energy metabolism, and biological activities such as growth and growth of microorganisms It is one of the essential nutrients that are indispensable.

  The phosphorus component removing means needs to be arranged on the supply water side of the reverse osmosis membrane module unit 7 in order to prevent microbial contamination of the reverse osmosis membrane module unit. The phosphorus removal apparatus is constituted by a phosphorus removal contact material 3 for efficiently removing a phosphorus component in the water to be treated, and a phosphorus removal column 3 ′ in which the phosphorus removal contact material 3 is filled in a container.

  In general, selective adsorption or precipitation separation using an adsorbent is known as a method for removing phosphorus. In the present invention, phosphorus components in the water to be treated are efficiently separated by adsorption separation or precipitation separation using a phosphorus removal contact material. Can be removed.

  Examples of the adsorbent include titanium, zirconium, or tin hydrous ferrite bonded to a resin carrier (see JP-A-9-187646), and also titanium, zirconium, tin, cerium, lanthanum, Organic polymer porous molded article carrying a composite oxide composed of one or more metal elements such as yttrium and one or more metal acid elements such as aluminum, silicon, or iron (see Japanese Patent Application Laid-Open No. 2007-14826) Alternatively, hydrotalcite (see JP 2008-49241 A), which is a layered double hydroxide mainly formed of magnesium and aluminum, is known. However, in the present invention, phosphorus in treated water is efficiently used. If it can be adsorbed and removed well, select the appropriate type according to the type of water to be treated without using the above materials. It can be.

On the other hand, as for the method by precipitation separation, as described in, for example, Japanese Patent Application Laid-Open No. 2007-268409 and Japanese Patent Application Laid-Open No. 2007-283223, calcium silicate or steel slag is used as a contact material, and this is treated. A method is known in which water is circulated and the phosphorus component is precipitated as hydroxyapatite [Ca ₁₀ (OH) ₂ (PO ₄ ) ₆ ] on the surface of the contact material, and can also be applied in the present invention. As a method for removing phosphorus, including any of the above methods, an appropriate method may be employed depending on conditions such as the type of raw water and the treatment capacity.

  In the present invention, as described above, the phosphorus removal contact material 3 having the phosphorus removal function described above is filled in the phosphorus removal column 3 ′, and the upper portion of the phosphorus removal column 3 ′ as shown in FIG. So that the water to be treated is passed from the bottom. The phosphorus removal contact material having a phosphorus removal function increases the contact area with the water to be treated as the particle size is small and the surface area is large, and the removal efficiency increases, but conversely, the water flow resistance of the water to be treated increases. Since the pressure of the supply pump becomes high, it is necessary to select and use the particle size appropriately. For example, when it is granulated, the preferable phosphorus removal contact material has a size of about 1 to 5 mm. In addition, the shape is generally granular, but the present invention is not particularly particular, and various shapes such as fibers and pellets can be used. It is appropriately selected depending on the water flow system and the like.

  Packing of the contact agent into the phosphorus removal column 3 ′ is performed as uniformly as possible so that the path of the water to be treated is not short-circuited when the water to be treated is passed from the top, because it is a fixed bed system. Is preferred. On the contrary, when water is passed from the lower portion as shown in FIG. 2, it is generally used as a fluidized bed system rather than a fixed bed system. Regardless of which of the above methods is employed, the thickness of the contact agent packed layer is determined by the space velocity (SV) at which the removal efficiency is optimal depending on the phosphorus concentration of the water to be treated, the type and shape of the contact agent used, etc. ).

  The material of the phosphorus removal column 3 'and the piping is not particularly limited, and may be a stainless steel alloy, PVC (polyvinyl chloride) resin, or general carbon steel as long as it is a material that is not corroded by the water to be treated. It is appropriately selected depending on the quality of the water to be treated, operating pressure, equipment cost, etc.

  In particular, when the precipitation method is used in a fixed bed system, the phosphorus removal contact agent may grow and stick by operating for a long time, and the contact efficiency of non-treated water may decrease. It is preferable to provide the phosphorus removal column 3 with a contact agent stirring device 4 for periodically stirring the phosphorus removal contact agent packed in the column. As a contact agent stirring device, it is preferable to send air to the packed bed by a compressor or a blower and stir. As shown in FIG. 2, when the water is passed from the lower part in the fluidized bed system, the contact agent stirrer 4 is not necessary because the contact material is hardly fixed as described above.

  Further, as a method of supplying the water to be treated to the phosphorus removal column 3, it is common to supply the water to be treated using the supply pump 2 of about several hundred kPa, but the water to be treated is supplied to the phosphorus removal column 3. If a sufficient water head difference can be obtained, it is possible to supply under natural flow without using the supply pump 2 as described above.

  In addition, even if only one phosphorus removal column can perform its function, when it is necessary to perform processing continuously, a plurality of preliminary phosphorus removal columns are provided in parallel, When the phosphorus removal capability is lowered, it is possible to continuously remove phosphorus by switching the flow path of the water to be treated. If the adsorbent is used after switching to a spare phosphorus removal column, it should be used again as a phosphorus removal adsorbent by appropriate regeneration using acid, alkali, or chloride solution. Is possible.

  Furthermore, the present invention prevents microbial contamination of the reverse osmosis membrane in the latter stage by efficiently removing the phosphorus component in the water to be treated, which is an essential nutrient of microorganisms. However, as shown in FIG. There is no problem even if a bactericide injection means, which is a reverse osmosis membrane sterilization means, is used in combination. In this case, due to the effect of removing phosphorus, the injection frequency and concentration of the bactericide can be reduced as compared with the conventional case.

  As described above, the present invention is characterized in that the phosphorus removing means is arranged upstream of the reverse osmosis membrane, and the pretreatment means and apparatus to be arranged upstream of the phosphorus removing means are particularly important. It does not limit and it can select suitably according to the kind and water quality of to-be-processed water. For example, when the water to be treated is seawater, rivers or lake water, coagulation sedimentation, sand filtration, microfiltration (MF) or ultrafiltration (UF) can be used alone or in combination. When water is sewage wastewater, aerobic biological treatment, anaerobic biological treatment, membrane bioreactor, or the like can be used alone or in combination in addition to the various filtration methods described above.

EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples and comparative examples, but the present invention is not limited to these examples.
<Example>
Using the treatment apparatus shown in FIG. 1, the factory wastewater after the biological treatment having the composition shown in Table 1 was treated with a reverse osmosis membrane. At that time, as a pretreatment upstream of the phosphorus removal apparatus of the present invention, an ultrafiltration (UF) membrane module was installed to remove turbid components in the wastewater.

The phosphorus removal apparatus uses a hydrotalcite represented by the chemical formula Mg ₆ Al ₂ (OH) .16CO ₃ .4H ₂ O as a phosphorus removal contact agent, granulated to a particle size of 2 to 3 mm, and has an inner diameter of 30 cm. A stainless steel column was packed with a thickness of about 54 cm so that the SV (space velocity) was 15 h- ¹ . The reverse osmosis membrane in the latter stage was operated under the conditions of a feed water flow rate of 2.0 m ³ / h and a permeate flow rate of 0.3 m ³ / h (recovery rate of 15%) using Toray's 4-inch diameter element TML10. The supply water pressure of the reverse osmosis membrane element at the initial stage of operation was 1.48 MPa, and the differential pressure between the reverse osmosis membrane element supply water inlet and the concentrated water outlet was 20 kPa. As a result of continuous operation while adjusting the operation pressure so that the same supply water amount and permeated water amount as above were obtained for about 3 months, the supply water pressure of the reverse osmosis membrane element after 3 months was 1.50 MPa, the reverse osmosis membrane The differential pressure between the element supply water inlet and the concentrated water outlet was 21 kPa. Table 1 shows the water quality analysis results of the UF feed water, UF filtered water, the RO feed water after removal of the phosphorus component, and the RO permeate.

Further, the reverse osmosis membrane element after operation for 3 months was taken out from the apparatus, disassembled, and observed on the membrane surface. As a result, it was confirmed that there was almost no deposit on the membrane surface.
<Comparative example>
As a comparative example, using the treatment apparatus shown in FIG. 3, factory wastewater after biological treatment having the composition shown in Table 1 exactly as in the example was treated with a reverse osmosis membrane. At that time, an ultrafiltration (UF) membrane module was installed as a pretreatment to remove turbid components in the wastewater. For reverse osmosis membranes, the reverse osmosis membrane type and flow rate conditions were as follows. Continuous operation was performed under exactly the same conditions as in the examples. The feed water pressure of the reverse osmosis membrane element at the initial stage of operation was 1.48 MPa, and the differential pressure between the feed water inlet of the reverse osmosis membrane element and the concentrated water outlet was 20 kPa, which was almost the same as in Example 1, but the reverse osmosis after 3 months The supply pressure of the membrane element was 1.57 MPa, and the differential pressure between the reverse osmosis membrane element supply water inlet and the concentrated water outlet was increased to about 50 kPa.

  Further, as in Example 1, the reverse osmosis membrane element after 3 months of operation was taken out from the apparatus, disassembled and observed on the membrane surface. As a result, a clear adhesive deposit was observed on the membrane surface of the reverse osmosis membrane. As a result of analysis, it was confirmed that organic substances considered to be microorganisms or metabolites from the microorganisms accounted for 98% of the total deposits.

1: treated water pipeline 2: supply pump 3: phosphorus removal contact agent 3 ': phosphorus removal column 4: contact agent stirring device 5: reverse osmosis membrane supply water pipeline 6: high pressure pump 7: reverse osmosis membrane module unit 8: reverse Osmotic membrane permeate water line 9: Reverse osmosis membrane concentrated water line 10: Bactericidal agent injection pump 11: Bactericidal agent injection line

Claims (4)

  A water treatment characterized by using a reverse osmosis membrane to supply treated water to the reverse osmosis membrane and separating the permeated water and concentrated water by adsorption separation or precipitation separation of phosphorus components in the treated water Method.   The water treatment method according to claim 1, wherein a fungicide is injected after removing a phosphorus component from the water to be treated.   In a water treatment apparatus comprising a reverse osmosis membrane module unit having a reverse osmosis membrane that separates permeated water and concentrated water and a high-pressure pump that supplies treated water to the reverse osmosis membrane module unit, A water treatment apparatus comprising means for adsorbing or separating and separating phosphorus components contained in water.   The water treatment apparatus according to claim 3, further comprising means for injecting a reverse osmosis membrane disinfectant after the means for adsorbing or separating the phosphorus component.

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