WO2009119300A1 - Method of pretreatment for separation with reverse osmosis membrane of water to be treated - Google Patents

Method of pretreatment for separation with reverse osmosis membrane of water to be treated Download PDF

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Publication number
WO2009119300A1
WO2009119300A1 PCT/JP2009/054463 JP2009054463W WO2009119300A1 WO 2009119300 A1 WO2009119300 A1 WO 2009119300A1 JP 2009054463 W JP2009054463 W JP 2009054463W WO 2009119300 A1 WO2009119300 A1 WO 2009119300A1
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Prior art keywords
water
alkali
treated
reverse osmosis
membrane
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PCT/JP2009/054463
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French (fr)
Japanese (ja)
Inventor
康弘 松井
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メタウォーター株式会社
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Priority to JP2010505515A priority Critical patent/JP5489982B2/en
Publication of WO2009119300A1 publication Critical patent/WO2009119300A1/en

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    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F5/00—Softening water; Preventing scale; Adding scale preventatives or scale removers to water, e.g. adding sequestering agents
    • C02F5/02—Softening water by precipitation of the hardness
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D21/00—Separation of suspended solid particles from liquids by sedimentation
    • B01D21/0012—Settling tanks making use of filters, e.g. by floating layers of particulate material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D21/00—Separation of suspended solid particles from liquids by sedimentation
    • B01D21/0039—Settling tanks provided with contact surfaces, e.g. baffles, particles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D21/00—Separation of suspended solid particles from liquids by sedimentation
    • B01D21/01—Separation of suspended solid particles from liquids by sedimentation using flocculating agents
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D21/00—Separation of suspended solid particles from liquids by sedimentation
    • B01D21/24—Feed or discharge mechanisms for settling tanks
    • B01D21/245—Discharge mechanisms for the sediments
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D21/00—Separation of suspended solid particles from liquids by sedimentation
    • B01D21/30—Control equipment
    • B01D21/305—Control of chemical properties of a component, e.g. control of pH
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/001—Processes for the treatment of water whereby the filtration technique is of importance
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/24—Treatment of water, waste water, or sewage by flotation
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
    • C02F1/441—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by reverse osmosis
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/66—Treatment of water, waste water, or sewage by neutralisation; pH adjustment
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00—Nature of the contaminant
    • C02F2101/30—Organic compounds
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F9/00—Multistage treatment of water, waste water or sewage

Definitions

  • the present invention relates to a pretreatment method for water to be used for membrane filtration of seawater and other water to be treated with a reverse osmosis membrane.
  • a microfiltration membrane or an ultrafiltration membrane When seawater or other treated water is subjected to membrane filtration with a reverse osmosis membrane, a microfiltration membrane or an ultrafiltration membrane is generally installed in the preceding stage. However, if the treated water is passed through the microfiltration membrane or ultrafiltration membrane without treatment, calcium and magnesium, etc. that are dissolved in the treated water and may form scale, floating substances, Microfiltration membranes and ultrafiltration membranes are clogged in a short time by organic substances, and continuous membrane filtration operation cannot be performed. Therefore, these are removed in advance before the microfiltration membrane and the ultrafiltration membrane to reduce the burden on the microfiltration membrane and the ultrafiltration membrane.
  • the organic film is inferior in acid resistance, when cleaning the causative substance of film fouling adhering to the film surface, it cannot be cleaned in a short time by immersing the film in strong acid, and the weak acid solution There was a problem that it was necessary to wash the film by immersing it in it for a long time.
  • Japanese Patent Application Laid-Open No. 2000-24673 introduces seawater to a fluidized calcium removal apparatus including a crystallization reaction tank and a treated water introduction tank, adds alkali, and removes calcium in the crystallization reaction tank. Thereafter, a pretreatment method for separation of seawater with a reverse osmosis membrane is disclosed, in which after coagulation precipitation is performed in a coagulation tank, solid-liquid separation is performed in a sand filtration device. In the method of Japanese Patent Laid-Open No.
  • the object of the present invention is to solve the above-mentioned problems of the prior art, perform membrane filtration at a much higher flux than before, and separate and remove floating substances and organic substances more reliably than before. Then, it is providing the pre-processing method for reverse osmosis membrane separation which can reduce the burden of a reverse osmosis membrane of a back
  • the reverse osmosis membrane separation can be used for various purposes including seawater desalination.
  • the pretreatment method for reverse osmosis membrane separation of the water to be treated according to the present invention made to solve the above-mentioned problems is performed by adding an alkaline agent to the water to be treated and adjusting the pH to 9.0 or more.
  • the components dissolved in the water to be treated and capable of forming scales are precipitated as insoluble substances, and a part of the precipitates produced by the alkali agglomeration operation is settled and separated, and then the pH is 9.0 or more.
  • the flocs are formed by adding the flocculant while maintaining the environment, and using the remaining precipitates as agglomeration nuclei, followed by filtration using an alkali-resistant and acid-resistant filter body to form a scale.
  • the floating substances and organic substances in the water to be treated are also taken into the floc and removed. That is, according to the pretreatment method of the present invention, floating substances and organic substances are removed from the water to be treated together with calcium and magnesium. Therefore, it is possible to reduce the filtration resistance in the subsequent filter body in the aggregation step. Further, according to this pretreatment method, it is possible to remove calcium, magnesium, floating substances and organic substances from the water to be treated, and to reduce the burden on the reverse osmosis membrane in the subsequent stage of the filter body.
  • alkaline aggregation is an operation sometimes referred to as alkali coagulation, and refers to the addition of an alkali agent to precipitate calcium and magnesium.
  • aggregation simply refers to forming flocs using a flocculant.
  • a filter refers to a membrane or non-membrane filter medium having a pore diameter of 2 nm or more and 10 ⁇ m or less, and is a concept including a filtration membrane.
  • the alkali-resistant and acid-resistant filter is a ceramic filter, and has a flux of 6 m 3 / m 2 / day or more. It is preferable to filter with a membrane.
  • Membrane filtration flux may be 6 m 3 / m 2 / day or more if a strong ceramic filter body is used as an alkali and acid resistant filter body compared to organic filter bodies. Because it can. And by increasing the membrane filtration flux, the membrane area required for filtration after alkali flocculation and flocculation using a flocculating agent can be reduced compared to organic membranes, and the pretreatment equipment can be made more compact Because it becomes possible.
  • ASTM Standard Test Method for Silent Density Index of Water D4189-95
  • SDI 15 (1-T 0 / T 15 ) ⁇ 100/15 T 0 : Time (seconds) required to filter 500 ml of the initial sample when the sample is filtered at a pressure of 206 kPa using a membrane filter having a pore diameter of 0.45 ⁇ m and a diameter of 47 mm T 15 : The time (seconds) required to filter 500 ml of the sample after 15 minutes of filtration
  • water to be treated with a large SDI has a tendency to increase the filtration resistance, and the microfiltration membrane or the like is blocked earlier.
  • the SDI value of the water supplied to a reverse osmosis membrane is 4 or less.
  • an acid having a pH of 2 or less is used against fouling accompanied by an increase in membrane pressure difference of the alkali-resistant and acid-resistant filter. It is preferable to perform acid cleaning of the filter body. This is because by performing acid cleaning of the filter using a strong acid having a pH of 2 or less, such as hydrochloric acid, scales accumulated on the filter surface of the filter and iron-based fouling substances can be quickly eluted. And by eluting scales and fouling substances promptly, it is possible to shorten the time required for acid cleaning and increase the operating rate of the pretreatment equipment. In addition, since the filter body which comprises this invention has acid resistance, a filter body is not damaged by the acid washing by strong acid below pH2.
  • ferric chloride which exhibits a high coagulation effect in the alkaline region of pH 9.0 to 11, is used as the coagulant, precipitates generated as a result of alkali coagulation are used as coagulation nuclei to effectively float floating substances and organic substances. It is because it can be made.
  • the alkali aggregation operation is performed using an upward flow contact method.
  • an upward flow method in which the water to be treated and the alkaline agent flow upward, the alkali agent and the nuclear particles having a specific gravity greater than that of the water to be treated are brought into contact with the alkaline agent, the alkali-aggregated core particles and the water to be treated.
  • An example of a pretreatment method for reverse osmosis membrane separation of water to be treated according to the present invention includes, as shown in FIG. 1, an alkali flocculation step using an alkali flocculation device 1, a flocculation step using a flocculation mixing tank 2, A membrane filtration step using a filter body (ceramic membrane) 3 having alkali resistance and acid resistance.
  • seawater can be mentioned as the to-be-processed water processed by an example of this pre-processing method.
  • Seawater, pH 8 before and after, the hardness Ca 2+ concentration of about 20 meq / L has a high water.
  • the water to be treated (seawater) is introduced and the alkali agent is injected, and the seawater and the alkali agent are mixed.
  • the introduction of seawater as water to be treated is performed at the lower part of the alkali flocculation apparatus 1, and the alkali agent is injected at the upper part of the alkali flocculation apparatus 1.
  • seawater and an alkaline agent are mixed using an upward flow contact method. That is, in the alkali aggregating apparatus 1, seawater extruded from the lower part and an alkaline agent having a large specific gravity to be settled from the upper part efficiently come into contact with each other.
  • NaOH slaked lime Ca (OH) 2 , sodium carbonate (Na 2 CO 3 ), or the like
  • the reason why calcium carbonate crystallizes in this way is that the solubility of calcium carbonate decreases due to an increase in pH and becomes supersaturated, and a part of dissolved calcium in seawater becomes insoluble.
  • a treatment operation for causing such a reaction to the treated water is referred to as an alkali agglomeration operation.
  • a mixing method of the water to be treated and the alkaline agent in the alkali aggregating apparatus 1 in addition to the upward flow method, a water flow stirring method in which a multistage bypass wall is provided, a stirring blade or the like in the device, and the like. You may use the mechanical stirring system which provides a stirring means.
  • the addition amount of the alkaline agent in the alkali flocculation apparatus 1 is set so that the pH of the effluent water from the alkali flocculation apparatus 1 is 9.0 or more.
  • the pH of the effluent water is less than 9.0, precipitation and flocculation of calcium and magnesium in the alkali flocculation apparatus 1 become insufficient, and calcium and magnesium dissolved in water to be treated having high hardness such as seawater are supersaturated.
  • the alkali flocculation apparatus 1 and the flocculation / mixing tank 2 reach the subsequent stage filter in the state.
  • the water to be treated whose pH is set to 9.0 or more by the alkali flocculation in the alkali flocculation apparatus 1 flows down into the flocculation mixing tank 2. Therefore, in the flocculation mixing tank 2, a flocculating agent that exhibits a flocculating effect in this environment is added to the water to be treated.
  • an aggregating agent for example, ferric chloride is used.
  • flocs are formed in which fine particles precipitated by alkali flocculation in the alkali flocculation apparatus 1 are formed as flocculation nuclei.
  • floating substances or organic substances in the water to be treated are taken into the floc.
  • seawater since seawater has low turbidity, a sufficient coagulation effect cannot be obtained even if the coagulant is directly injected. Therefore, it is effective to form aggregated nuclei by performing alkali aggregation before the aggregation process as in the present invention.
  • the water to be treated that has passed through the flocculation / mixing tank 2 is sent to the alkali- and acid-resistant filter body 3 and subjected to membrane filtration.
  • the alkali-resistant and acid-resistant filter body 3 for example, a ceramic monolith membrane having a membrane pore diameter of 0.1 ⁇ m can be used.
  • the membrane shape of the filter body 3 is not necessarily limited to the monolith membrane, and may be a flat membrane or a tubular membrane.
  • floating substances and organic substances are membrane-separated by the alkali- and acid-resistant filter 3.
  • the membrane filtered water obtained by filtration with the filter body 3 has an SDI of about 3.0, and can be supplied to the reverse osmosis membrane.
  • the inflowing water flowing into the alkali-resistant and acid-resistant filter 3 has a certain degree of hardness reduced by the alkali flocculation process in the alkali flocculation apparatus 1 and the flocculation process in the flocculation mixing tank 2, but it still generates scale. Is remaining and is alkaline. Therefore, it is inevitable that a scale such as calcium carbonate is formed on the filtration surface of the alkali-resistant and acid-resistant filter body 3 by membrane filtration of the influent water. For this reason, if the filtration operation is continued, the membrane surface of the alkali-resistant and acid-resistant filter body 3 is agglomerated by the addition of ferric chloride in the agglomeration and mixing tank 2 due to this scale formation. Things derived from things (floc) gradually accumulate as fouling substances.
  • the alkali-resistant and acid-resistant filter body 3 is periodically acid-washed according to the increase in the membrane differential pressure due to the accumulation of fouling substances.
  • this acid cleaning accumulated fouling substances are dissolved and removed.
  • the filter body 3 used in the present invention is excellent in acid resistance, there is no film deterioration even when acid cleaning with a known strong acid having a pH of 2 or less is performed. Therefore, membrane fouling can be eliminated in a short time by acid cleaning using a strong acid having a pH of 2 or lower.
  • stable operation over a long period of time is possible while quickly recovering the increase in membrane differential pressure. That is, according to the present invention, the quality of the pretreated water does not deteriorate for a long time.
  • FIG. 2 shows a first embodiment of a pretreatment apparatus used in a pretreatment method for reverse osmosis membrane separation of water to be treated according to the present invention.
  • the pretreatment device of the first embodiment includes a flocculation / separation device 10 and a filter body 22. And the water (pretreatment water) processed with this pretreatment apparatus is filtered with the reverse osmosis membrane which is not illustrated, and is separated into permeated water and concentrated water.
  • the water to be treated to be treated by this pretreatment device for example, high-hardness water having a total hardness concentration of 300 mg / L (CaCO 3 equivalent concentration) or more, such as seawater or brine.
  • the total hardness concentration can be determined by calculating the sum of calcium and magnesium concentrations in water using ICP emission spectroscopic analysis in accordance with JIS K0101.
  • the aggregating and separating apparatus 10 has a cylindrical shape, and the water to be treated can flow between the alkali aggregating tank 11, the aggregating and sedimenting tank 12 provided above the alkali aggregating tank 11, and the alkali aggregating tank 11 and the agglomerating and sedimenting tank 12. And a partition plate 15 for partitioning.
  • the alkali flocculation tank 11 corresponds to the alkali flocculation apparatus 1 of the above example
  • the flocculation settling tank 12 corresponds to the flocculation mixing tank 2 of the above example.
  • the alkali agglomeration tank 11 is provided with a treated water inlet 13 as treated water injection means and an alkaline inlet 14 as alkaline agent injection means.
  • the water to be treated that has flowed from the water to be treated inlet 13 and the alkali agent injected through the alkali inlet 14 come into contact with each other, and the water is stirred in an upward flow. That is, an upward flow contact method is realized. Therefore, in the alkali flocculation tank 11, the pH of the water to be treated is increased, and calcium and magnesium in the water to be treated are precipitated as white turbid substances (carbonates or hydroxides).
  • an alkaline agent sodium hydroxide, sodium carbonate, etc.
  • water flow stirring refers to stirring using the flow (water flow) itself of water flowing into the apparatus, not mechanical stirring using a stirrer or the like. Specifically, by setting the cross-sectional area of the tank with respect to the design inflow of the water to be treated and the alkaline agent so that the Reynolds number, which is an indicator of hydraulic disturbance in the tank, is 10,000 or more, Water agitation can be realized. If it does in this way, the pre-process of high hardness raw
  • the partition plate 15 has a plurality of nozzles 16 protruding toward the coagulation sedimentation tank 12 side. Then, the water to be treated and the cloudy substance precipitated in the alkali coagulation tank 11 flow from the alkali coagulation tank 11 to the coagulation sedimentation tank 12 through the nozzle 16.
  • a coagulant injection port 18 as a coagulant injection means, a water outlet to be treated, and a stirrer 21 are provided in the upper part of the coagulation sedimentation tank 12.
  • the sludge discharge port 20 is provided in the upper part of the coagulation sedimentation tank 12.
  • a coagulant such as ferric chloride with respect to the mixture of the water to be treated and the cloudy substance flowing from the alkali coagulation tank 11 has a concentration of, for example, 1 to 6 mg / L (iron equivalent) ) And mixed.
  • the white turbid substance flowing in from the alkali flocculation tank 11 flows from the lower part to the upper part of the flocculation settling tank 12 and comes into contact with the flocculant added at the upper part to form a floc, but a part of the white turbid substance flows to the upper part. Settling in between. In this floc formation process, floating substances and organic substances contained in the water to be treated are also taken into the floc.
  • a part of the floc formed by adding the flocculant settles in the flocculent sedimentation tank 12 and accumulates in the accumulating portion 17 on the partition plate 15 together with the cloudy substance that settles while flowing from the lower part to the upper part of the flocculent sedimentation tank 12. .
  • the accumulated floc and cloudy substance are periodically withdrawn from the sludge discharge port 20 as a mud discharge means.
  • it can be appropriately discharged by intermittently opening or closing a gate valve (not shown) provided on the rear stage side of the sludge discharge port 20 or by continuous opening.
  • waste mud may be performed using a water head difference, and may be performed using a drainage pump.
  • the filter body 22 provided in the back
  • FIG. Therefore, pretreatment water from which components (calcium and magnesium), floatable substances and organic substances that may form a scale can be obtained by sedimentation separation in the flocculation separation apparatus 10 and filtration through the filter 22 can be obtained.
  • the filter body 22 for example, an alkali-resistant and acid-resistant microfiltration membrane or an ultrafiltration membrane can be used.
  • FIG. 3 shows a second embodiment of the pretreatment apparatus used in the pretreatment method for reverse osmosis membrane separation of water to be treated according to the present invention.
  • the pretreatment device of the second embodiment includes a flocculation / separation tank 30 having an alkali flocculation tank and a flocculation / mixing tank, and a filter body 36. And the water (pretreatment water) processed with this pretreatment apparatus is filtered with the reverse osmosis membrane which is not illustrated, and is separated into permeated water and concentrated water.
  • the flocculation / separation tank 30 includes a treated water storage tank 31, an alkali flocculation tank 32, and an agglomeration mixing tank 33. It communicates with. Therefore, the water to be treated that has flowed into the flocculation / separation tank 30 is stored in the water to be treated 31 and then flows from the lower part of the water to be treated 31 into the alkali flocculation tank 32.
  • the alkali flocculation tank 32 corresponds to the alkali flocculation apparatus 1 of the above example
  • the flocculation mixing tank 33 corresponds to the flocculation / mixing tank 2 of the above example.
  • the alkali flocculation tank 32 in this embodiment includes a stirrer 34.
  • an alkali agent such as sodium hydroxide is added to the water to be treated, and the water to be treated and the alkali agent are mixed by the stirrer 34.
  • pH of to-be-processed water rises and calcium and magnesium in to-be-processed water precipitate as a cloudy substance (carbonate or hydroxide).
  • the injection amount of the alkaline agent can be adjusted by a known means so that the pH of the water flowing out from the coagulation / separation tank 30 becomes 9.0 or more.
  • the cloudy substance precipitated in the alkali flocculation tank 32 is settled and separated in the alkali flocculation tank 32.
  • the cloudy substance that has not settled in the alkali coagulation tank 32 and the water to be treated flow into the coagulation mixing tank 33 from the lower part of the alkali coagulation tank 32.
  • a coagulant such as ferric chloride is added to the water to be treated and the cloudy substance flowing from the alkali coagulation tank 32, and the water to be treated, the cloudy substance and the flocculant are mixed by the stirrer 35.
  • the cloudy substance aggregates to form flocs by the addition of the flocculant.
  • floating substances and organic substances contained in the water to be treated are also taken into the floc.
  • pretreatment water from which components (calcium and magnesium), floatable substances and organic substances that may form scales are removed is obtained by sedimentation separation in the alkali coagulation tank 32 and filtration in the filter body 36.
  • a ceramic membrane can be used as the filter body 36.
  • a membrane having acid resistance is used as the filter body. Therefore, when the filter body is clogged, the pH is 2 or less. Can be washed with strong acid. That is, in the pretreatment devices of the first and second embodiments, fouling can be eliminated in a short time.
  • Example 1 Seawater having a pH of around 8 was treated using the pretreatment apparatus shown in FIG. Specifically, seawater was caused to flow through the flocculation / separation apparatus 10 in FIG. 2 in an upward flow with a linear velocity of 10 m / hr or more, and NaOH was added to the seawater as an alkaline agent. And the alkali aggregation was performed on the conditions from which pH of the seawater after alkali agent addition was set to 9.0 or more. Thereafter, ferric chloride as a coagulant is 1 to 6 mg / L (converted value of iron) into seawater (total dissolved component (TDS) concentration 3.5%) introduced into the coagulation sedimentation tank 12 through the alkali coagulation tank 11. As)).
  • ferric chloride as a coagulant is 1 to 6 mg / L (converted value of iron) into seawater (total dissolved component (TDS) concentration 3.5%) introduced into the coagulation sedimentation tank 12 through the alkali coagulation tank 11. As)).
  • the seawater to which the flocculant was added was filtered through a ceramic monolith membrane 3 (microfiltration ceramic membrane) having a membrane pore diameter of 0.1 ⁇ m.
  • the filtration flux at that time was 6 to 8 m 3 / m 2 / day, and no increase in the differential pressure exceeding 100 KPa was observed even after 2000 hours.
  • the TDS can be determined by measuring the weight of the residue when the sample (seawater) is heated at 110 ° C. to remove moisture.
  • Example 2 Using the apparatus shown in FIG. 3, seawater was treated by changing the pH after the alkali flocculation operation. Specifically, when seawater is treated with a membrane filtration flux of 7 m 3 / m 2 / day, the change in transmembrane pressure difference between the case where the pH after alkali aggregation is 7.8 and the case where it is 9.5. was measured. The same flocculant as that used in Example 1 was used. The transmembrane pressure difference was determined by measuring the operating pressure on the primary side and the secondary side of the membrane with a pressure gauge and calculating the difference. The results are shown in FIG.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Hydrology & Water Resources (AREA)
  • Engineering & Computer Science (AREA)
  • Environmental & Geological Engineering (AREA)
  • Water Supply & Treatment (AREA)
  • Organic Chemistry (AREA)
  • Separation Using Semi-Permeable Membranes (AREA)
  • Separation Of Suspended Particles By Flocculating Agents (AREA)
  • Removal Of Specific Substances (AREA)

Abstract

A method of pretreatment for separation with a reverse osmosis membrane is provided in which membrane filtration can be conducted at a far higher flow velocity than in conventional methods and suspended solids and organic substances can be separated/removed with higher certainty than in conventional methods to thereby mitigate the burden to be imposed on a reverse osmosis membrane in a later stage. The pretreatment method is characterized by: adding an alkali to raw water to be treated and regulating the pH thereof to 9.0 or higher to precipitate, as an insoluble substance, an ingredient dissolved in the raw water and capable of scale formation; settling and separating part of the precipitate generated by the alkali flocculation; subsequently adding a flocculant to the water while maintaining the environment having a pH of 9.0 or higher to form flocs using the remaining precipitate as flocculation nuclei; and then filtering the water through a filter medium having alkali resistance and acid resistance to remove the ingredient capable of scale formation, suspended solids, and organic substances.

Description

被処理水の逆浸透膜による分離のための前処理方法Pretreatment method for separation by reverse osmosis membrane of treated water
　本発明は、海水その他の被処理水を逆浸透膜で膜ろ過する際に使用される被処理水の前処理方法に関するものである。 The present invention relates to a pretreatment method for water to be used for membrane filtration of seawater and other water to be treated with a reverse osmosis membrane.
　海水その他の被処理水を逆浸透膜で膜ろ過する際には、その前段に精密ろ過膜もしくは限外ろ過膜が設置されるのが一般的である。しかし、被処理水を精密ろ過膜もしくは限外ろ過膜に無処理のまま通水すると、被処理水に溶解しておりスケールを形成する可能性のあるカルシウム及びマグネシウム等や、浮遊性物質や、有機物によって精密ろ過膜や限外ろ過膜が短時間で閉塞してしまい、連続膜ろ過運転が行えなくなる。そこで、精密ろ過膜や限外ろ過膜の前段でこれらを予め除去し、精密ろ過膜や限外ろ過膜の負担を軽減することが行われている。 When seawater or other treated water is subjected to membrane filtration with a reverse osmosis membrane, a microfiltration membrane or an ultrafiltration membrane is generally installed in the preceding stage. However, if the treated water is passed through the microfiltration membrane or ultrafiltration membrane without treatment, calcium and magnesium, etc. that are dissolved in the treated water and may form scale, floating substances, Microfiltration membranes and ultrafiltration membranes are clogged in a short time by organic substances, and continuous membrane filtration operation cannot be performed. Therefore, these are removed in advance before the microfiltration membrane and the ultrafiltration membrane to reduce the burden on the microfiltration membrane and the ultrafiltration membrane.
　例えば、特開平９－２４８４２９号公報には、海水にアルカリを添加してｐＨを９程度まで上げ、スケールを形成する可能性のある成分を炭酸塩等の非溶解物質として析出させ、析出した非溶解物質を中空糸状の有機材料製精密ろ過膜によって分離除去する前処理方法が開示されている。しかし、有機膜は膜面強度が低いために膜ろ過流束をあまり高めることができず、有機膜を用いたろ過における実用的な流束は２ｍ３／ｍ２／日以下である。このため、処理水量を確保するためには膜面積を大きくする必要があった。 For example, in Japanese Patent Laid-Open No. 9-248429, alkali is added to seawater to raise the pH to about 9, and components that may form scale are precipitated as insoluble substances such as carbonates. A pretreatment method is disclosed in which a dissolved substance is separated and removed by a microfiltration membrane made of a hollow fiber organic material. However, since the membrane strength of the organic membrane is low, the membrane filtration flux cannot be increased so much, and the practical flux in filtration using the organic membrane is 2 m 3 / m 2 / day or less. For this reason, in order to secure the amount of treated water, it was necessary to increase the membrane area.
　また有機膜は耐酸性に劣るため、膜面に付着した膜ファウリングの原因物質を酸洗浄する場合に、強酸中への膜の浸漬による短時間での洗浄をすることができず、弱酸溶液中へ膜を長時間浸漬して洗浄する必要があるという問題があった。 In addition, since the organic film is inferior in acid resistance, when cleaning the causative substance of film fouling adhering to the film surface, it cannot be cleaned in a short time by immersing the film in strong acid, and the weak acid solution There was a problem that it was necessary to wash the film by immersing it in it for a long time.
　この他、特開２０００－２４６７３号公報には、晶析反応槽と被処理水導入槽とを備える流動式カルシウム除去装置に海水を導いてアルカリを加え、晶析反応槽においてカルシウム除去を行い、その後、凝集槽において凝集沈殿を行ったうえで砂ろ過装置において固液分離する、海水の逆浸透膜による分離のための前処理方法が開示されている。この特開２０００－２４６７３号公報の方法では固液分離手段として砂ろ過装置を使用しているため、ろ過の対象となる粒子の粒子径が精密ろ過膜及び限外ろ過膜に比べて大きく、且つ、砂ろ過装置の使用により前処理設備が大型化するという問題があった。 In addition, Japanese Patent Application Laid-Open No. 2000-24673 introduces seawater to a fluidized calcium removal apparatus including a crystallization reaction tank and a treated water introduction tank, adds alkali, and removes calcium in the crystallization reaction tank. Thereafter, a pretreatment method for separation of seawater with a reverse osmosis membrane is disclosed, in which after coagulation precipitation is performed in a coagulation tank, solid-liquid separation is performed in a sand filtration device. In the method of Japanese Patent Laid-Open No. 2000-24673, since a sand filtration device is used as a solid-liquid separation means, the particle size of particles to be filtered is larger than that of a microfiltration membrane and an ultrafiltration membrane, and There has been a problem that the use of a sand filter increases the size of the pretreatment equipment.
　従って、本発明の目的は、上記した従来技術の問題点を解決し、従来よりもはるかに高流束で膜ろ過を行うことができ、しかも従来よりも確実に浮遊性物質及び有機物を分離除去して後段の逆浸透膜の負担を軽減することができる、逆浸透膜分離のための前処理方法を提供することである。なお、逆浸透膜分離は、海水淡水化をはじめ、各種用途に利用することができる。 Therefore, the object of the present invention is to solve the above-mentioned problems of the prior art, perform membrane filtration at a much higher flux than before, and separate and remove floating substances and organic substances more reliably than before. Then, it is providing the pre-processing method for reverse osmosis membrane separation which can reduce the burden of a reverse osmosis membrane of a back | latter stage. The reverse osmosis membrane separation can be used for various purposes including seawater desalination.
　上記の課題を解決するためになされた本発明の被処理水の逆浸透膜分離のための前処理方法は、被処理水にアルカリ剤を添加してｐＨを９．０以上に調整することにより、前記被処理水に溶解しておりスケールを形成する可能性のある成分を非溶解性物質として析出させ、そのアルカリ凝集操作によって生じた析出物の一部を沈降分離した後に、ｐＨ９．０以上の環境を維持したまま凝集剤を添加して残存する析出物を凝集核とするフロックを形成させたうえ、耐アルカリ性かつ耐酸性のろ過体を用いてろ過を行い、スケールを形成する可能性のある成分、浮遊性物質及び有機物を除去することを特徴とするものである。このように、被処理水（例えば海水）のｐＨを９．０以上にまで高めてアルカリ凝集を行えば、被処理水に含まれているカルシウム及びマグネシウム等のスケールを形成する可能性のある成分の一部が非溶解化（析出）する。そして、アルカリ凝集後の被処理水に対してｐＨが９．０以上の環境で凝集機能を発揮する凝集剤を添加すれば、アルカリ凝集操作で発生した微細粒子を凝集核としてフロックが形成される。ここで、この凝集剤を用いた凝集工程においては、被処理水中の浮遊性物質及び有機物もフロック中に取り込まれて除去される。即ち、本発明の前処理方法によれば、カルシウム及びマグネシウムと共に、浮遊性物質や、有機物も被処理水から除去される。従って、凝集工程の後段のろ過体におけるろ過抵抗を低減することができる。また、この前処理方法によれば、被処理水からカルシウム、マグネシウム、浮遊性物質および有機物を除去して、ろ過体の後段の逆浸透膜の負担を軽減することが可能となる。なお、本発明において、「アルカリ凝集」とは、アルカリ凝析とも称されることがある操作であり、アルカリ剤を添加してカルシウムおよびマグネシウムを析出させることを指す。また、本発明において、単に「凝集」というときは、凝集剤を用いてフロックを形成することを指す。更に、本発明において、ろ過体とは、孔径が２ｎｍ以上１０μｍ以下の膜製または非膜製のろ材を指し、ろ過膜をも含む概念である。 The pretreatment method for reverse osmosis membrane separation of the water to be treated according to the present invention made to solve the above-mentioned problems is performed by adding an alkaline agent to the water to be treated and adjusting the pH to 9.0 or more. The components dissolved in the water to be treated and capable of forming scales are precipitated as insoluble substances, and a part of the precipitates produced by the alkali agglomeration operation is settled and separated, and then the pH is 9.0 or more. The flocs are formed by adding the flocculant while maintaining the environment, and using the remaining precipitates as agglomeration nuclei, followed by filtration using an alkali-resistant and acid-resistant filter body to form a scale. It is characterized by removing certain components, floating substances and organic substances. Thus, if the pH of the water to be treated (for example, seawater) is increased to 9.0 or higher and alkali agglomeration is performed, components that may form scales such as calcium and magnesium contained in the water to be treated A part of is dissolved (precipitated). If a flocculant that exhibits a coagulation function in an environment having a pH of 9.0 or higher is added to the water to be treated after alkali aggregation, flocs are formed using fine particles generated by the alkali aggregation operation as aggregation nuclei. . Here, in the flocculation process using this flocculating agent, the floating substances and organic substances in the water to be treated are also taken into the floc and removed. That is, according to the pretreatment method of the present invention, floating substances and organic substances are removed from the water to be treated together with calcium and magnesium. Therefore, it is possible to reduce the filtration resistance in the subsequent filter body in the aggregation step. Further, according to this pretreatment method, it is possible to remove calcium, magnesium, floating substances and organic substances from the water to be treated, and to reduce the burden on the reverse osmosis membrane in the subsequent stage of the filter body. In the present invention, “alkaline aggregation” is an operation sometimes referred to as alkali coagulation, and refers to the addition of an alkali agent to precipitate calcium and magnesium. In the present invention, the term “aggregation” simply refers to forming flocs using a flocculant. Furthermore, in the present invention, a filter refers to a membrane or non-membrane filter medium having a pore diameter of 2 nm or more and 10 μm or less, and is a concept including a filtration membrane.
　本発明の被処理水の逆浸透膜分離のための前処理方法においては、前記耐アルカリ性かつ耐酸性のろ過体が、セラミック製ろ過体であって、６ｍ３／ｍ２／日以上の流束で膜ろ過することが好ましい。有機性のろ過体に比べて膜面強度が高く、強靭なセラミック製ろ過体を耐アルカリ性かつ耐酸性のろ過体として用いれば、膜ろ過流束を６ｍ３／ｍ２／日以上とすることができるからである。そして、膜ろ過流束を高めることによって、アルカリ凝集および凝集剤を用いた凝集の後のろ過に必要な膜面積を有機膜に比較して小さくすることができ、前処理設備をより小型化することが可能となるからである。
　なお、本発明において、膜ろ過流束を６ｍ３／ｍ２／日以上に高めた場合であっても、従来の有機膜が実現している逆浸透膜への前処理水の水質（ＳＤＩ＝３.０）を達成することは可能である。なお、ＳＤＩは“Ｓｉｌｔ　Ｄｅｎｓｉｔｙ　Ｉｎｄｅｘ”の頭文字であり、水中に分散している微細粒子量を表す指標である。因みに、ＳＤＩは、ＡＳＴＭ（Ｓｔａｎｄａｒｄ　Ｔｅｓｔ　Ｍｅｔｈｏｄ　ｆｏｒ　Ｓｉｌｔ　Ｄｅｎｓｉｔｙ　Ｉｎｄｅｘ　ｏｆ　Ｗａｔｅｒ　Ｄ４１８９－９５）に従い測定することができる。具体的には、以下の計算式を用いてＳＤＩを算出することができる。
　　ＳＤＩ１５＝（１－Ｔ０　／Ｔ１５）×１００／１５
Ｔ０　：孔径０．４５μｍ、直径４７ｍｍのメンブレンフィルターを用いて圧力２０６ｋＰａで試料をろ過した際に初期の試料５００ｍｌをろ過するのに要する時間（秒）
Ｔ１５：ろ過を１５分継続した後、更に試料５００ｍｌをろ過するのに要する時間（秒）
　ここで、一般に、ＳＤＩの大きい被処理水はろ過抵抗が大きくなる傾向を示し、精密ろ過膜等の閉塞をより早期にもたらすことが知られている。なお、海水や下水などを前処理した後に逆浸透膜へ供給する場合、逆浸透膜への供給水のＳＤＩ値は４以下であることが好ましいとされている。 In the pretreatment method for reverse osmosis membrane separation of the water to be treated according to the present invention, the alkali-resistant and acid-resistant filter is a ceramic filter, and has a flux of 6 m 3 / m 2 / day or more. It is preferable to filter with a membrane. Membrane filtration flux may be 6 m 3 / m 2 / day or more if a strong ceramic filter body is used as an alkali and acid resistant filter body compared to organic filter bodies. Because it can. And by increasing the membrane filtration flux, the membrane area required for filtration after alkali flocculation and flocculation using a flocculating agent can be reduced compared to organic membranes, and the pretreatment equipment can be made more compact Because it becomes possible.
In the present invention, even when the membrane filtration flux is increased to 6 m 3 / m 2 / day or more, the quality of the pretreated water (SDI = SDI = to the reverse osmosis membrane realized by the conventional organic membrane) It is possible to achieve 3.0). SDI is an acronym for “Silt Density Index” and is an index representing the amount of fine particles dispersed in water. Incidentally, SDI can be measured according to ASTM (Standard Test Method for Silent Density Index of Water D4189-95). Specifically, the SDI can be calculated using the following calculation formula.
SDI 15 = (1-T 0 / T 15 ) × 100/15
T 0 : Time (seconds) required to filter 500 ml of the initial sample when the sample is filtered at a pressure of 206 kPa using a membrane filter having a pore diameter of 0.45 μm and a diameter of 47 mm
T 15 : The time (seconds) required to filter 500 ml of the sample after 15 minutes of filtration
Here, it is generally known that water to be treated with a large SDI has a tendency to increase the filtration resistance, and the microfiltration membrane or the like is blocked earlier. In addition, when supplying seawater, sewage, etc. to a reverse osmosis membrane after pre-processing, it is preferable that the SDI value of the water supplied to a reverse osmosis membrane is 4 or less.
　本発明の被処理水の逆浸透膜による分離のための前処理方法おいては、前記耐アルカリ性かつ耐酸性のろ過体の膜差圧上昇を伴ったファウリングに対して、ｐＨ２以下の酸で前記ろ過体の酸洗浄を行うことが好ましい。ｐＨ２以下の強酸、例えば塩酸を用いてろ過体の酸洗浄を行うことより、ろ過体のろ過面に蓄積したスケールや、鉄系のファウリング物質を速やかに溶出させることができるからである。そして、スケールやファウリング物質を速やかに溶出させることにより、酸洗浄に要する時間を短縮し、前処理設備の稼働率を高めることが可能となるからである。なお、本発明を構成するろ過体は、耐酸性を有するため、ｐＨ２以下の強酸による酸洗浄によってろ過体が損傷することはない。 In the pretreatment method for separation by the reverse osmosis membrane of the water to be treated of the present invention, an acid having a pH of 2 or less is used against fouling accompanied by an increase in membrane pressure difference of the alkali-resistant and acid-resistant filter. It is preferable to perform acid cleaning of the filter body. This is because by performing acid cleaning of the filter using a strong acid having a pH of 2 or less, such as hydrochloric acid, scales accumulated on the filter surface of the filter and iron-based fouling substances can be quickly eluted. And by eluting scales and fouling substances promptly, it is possible to shorten the time required for acid cleaning and increase the operating rate of the pretreatment equipment. In addition, since the filter body which comprises this invention has acid resistance, a filter body is not damaged by the acid washing by strong acid below pH2.
　本発明の被処理水の逆浸透膜による分離のための前処理方法おいては、前記凝集剤として塩化第二鉄を用いることが好ましい。ｐＨが９．０～１１のアルカリ領域において高い凝集効果を発揮する塩化第二鉄を凝集剤として用いれば、アルカリ凝集の結果生じた析出物を凝集核として、浮遊性物質および有機物を効率よくフロック化することができるからである。 In the pretreatment method for separation by the reverse osmosis membrane of the water to be treated of the present invention, it is preferable to use ferric chloride as the flocculant. If ferric chloride, which exhibits a high coagulation effect in the alkaline region of pH 9.0 to 11, is used as the coagulant, precipitates generated as a result of alkali coagulation are used as coagulation nuclei to effectively float floating substances and organic substances. It is because it can be made.
　そして、本発明の被処理水の逆浸透膜による分離のための前処理方法おいては、前記アルカリ凝集操作を、上向流式の接触手法を用いて行うことが好ましい。被処理水およびアルカリ剤を上向流で流す上向流式を用いて、アルカリ剤、アルカリ凝集した核粒子および被処理水を接触させれば、被処理水より比重の大きいアルカリ剤および核粒子が、比重の小さい被処理水（例えば海水）の中で分散する。従って、下向流でアルカリ剤、凝集した核粒子および被処理水を接触させる場合に比べ接触効率を上げることができるからである。 In the pretreatment method for separation of the water to be treated by the reverse osmosis membrane of the present invention, it is preferable that the alkali aggregation operation is performed using an upward flow contact method. Using an upward flow method in which the water to be treated and the alkaline agent flow upward, the alkali agent and the nuclear particles having a specific gravity greater than that of the water to be treated are brought into contact with the alkaline agent, the alkali-aggregated core particles and the water to be treated. However, it disperse | distributes in to-be-processed water (for example, seawater) with small specific gravity. Therefore, the contact efficiency can be increased as compared with the case where the alkali agent, the agglomerated core particles, and the water to be treated are brought into contact in a downward flow.
本発明の前処理方法の一例を示すブロック図である。It is a block diagram which shows an example of the pre-processing method of this invention. 本発明の前処理方法に用いる前処理装置の第１実施形態を示す説明図である。It is explanatory drawing which shows 1st Embodiment of the pre-processing apparatus used for the pre-processing method of this invention. 本発明の前処理方法に用いる前処理装置の第２実施形態を示す説明図である。It is explanatory drawing which shows 2nd Embodiment of the pre-processing apparatus used for the pre-processing method of this invention. 本発明の実施例におけるろ過時間と膜間差圧との関係を示すグラフである。It is a graph which shows the relationship between the filtration time and the transmembrane differential pressure in the Example of this invention.
　以下に本発明の好ましい実施形態を示す。
　本発明にかかる被処理水の逆浸透膜分離のための前処理方法の一例は、図１に示すように、アルカリ凝集装置１を用いるアルカリ凝集工程と、凝集混和槽２を用いる凝集工程と、耐アルカリ性および耐酸性を有するろ過体（セラミック膜）３を用いる膜ろ過工程とからなる。 Preferred embodiments of the present invention are shown below.
An example of a pretreatment method for reverse osmosis membrane separation of water to be treated according to the present invention includes, as shown in FIG. 1, an alkali flocculation step using an alkali flocculation device 1, a flocculation step using a flocculation mixing tank 2, A membrane filtration step using a filter body (ceramic membrane) 3 having alkali resistance and acid resistance.
　ここで、この前処理方法の一例で処理される被処理水としては、海水を挙げることができる。海水は、ｐＨが８前後で、Ｃａ２＋濃度が２０ｍｅｑ/Ｌ程度の硬度が高い水である。 Here, seawater can be mentioned as the to-be-processed water processed by an example of this pre-processing method. Seawater, pH 8 before and after, the hardness Ca 2+ concentration of about 20 meq / L has a high water.
　アルカリ凝集装置１では、被処理水（海水）の導入とアルカリ剤の注入をおこない、海水とアルカリ剤とが混合される。本実施形態におけるアルカリ凝集装置１では、被処理水としての海水の導入がアルカリ凝集装置１の下部で行われ、アルカリ剤の注入がアルカリ凝集装置１の上部で行われる。このアルカリ凝集装置１では、上向流式の接触手法を用いて海水とアルカリ剤とが混合される。すなわち、アルカリ凝集装置１の内部では、下部から押し出してくる海水と、上部から沈降しようとする比重の大きいアルカリ剤とが効率よく接触する。 In the alkali aggregating apparatus 1, the water to be treated (seawater) is introduced and the alkali agent is injected, and the seawater and the alkali agent are mixed. In the alkali flocculation apparatus 1 according to the present embodiment, the introduction of seawater as water to be treated is performed at the lower part of the alkali flocculation apparatus 1, and the alkali agent is injected at the upper part of the alkali flocculation apparatus 1. In the alkali aggregating apparatus 1, seawater and an alkaline agent are mixed using an upward flow contact method. That is, in the alkali aggregating apparatus 1, seawater extruded from the lower part and an alkaline agent having a large specific gravity to be settled from the upper part efficiently come into contact with each other.
　アルカリ剤としては、ＮａＯＨや、消石灰Ｃａ（ＯＨ）２や炭酸ナトリウム（Ｎａ２ＣＯ３）などを用いることができる。アルカリ剤としてＮａＯＨを使用した場合、以下の反応により炭酸カルシウムの結晶が生ずる。
　　Ｃａ（ＨＣＯ３）２＋ＮａＯＨ→ＣａＣＯ３↓＋ＮａＨＣＯ３＋Ｈ２Ｏ
　このようにして炭酸カルシウムが結晶化するのは、ｐＨが上昇したことにより炭酸カルシウムの溶解度が低下し、過飽和となって海水中の溶存態カルシウムの一部が非溶解化するためである。なお、本発明では、被処理水に対して、このような反応を起こさせるための処理操作をアルカリ凝集操作と称している。ここで、アルカリ凝集装置１における被処理水とアルカリ剤との混合方式としては、上記上向流式以外にも、多段の迂流壁を設けた水流撹拌方式や、装置内に撹拌羽根などの撹拌手段を設ける機械撹拌方式を用いても良い。 As the alkaline agent, NaOH, slaked lime Ca (OH) 2 , sodium carbonate (Na 2 CO 3 ), or the like can be used. When NaOH is used as the alkaline agent, calcium carbonate crystals are formed by the following reaction.
Ca (HCO 3 ) 2 + NaOH → CaCO 3 ↓ + NaHCO 3 + H 2 O
The reason why calcium carbonate crystallizes in this way is that the solubility of calcium carbonate decreases due to an increase in pH and becomes supersaturated, and a part of dissolved calcium in seawater becomes insoluble. In the present invention, a treatment operation for causing such a reaction to the treated water is referred to as an alkali agglomeration operation. Here, as a mixing method of the water to be treated and the alkaline agent in the alkali aggregating apparatus 1, in addition to the upward flow method, a water flow stirring method in which a multistage bypass wall is provided, a stirring blade or the like in the device, and the like. You may use the mechanical stirring system which provides a stirring means.
　アルカリ凝集装置１におけるアルカリ剤の添加量は、アルカリ凝集装置１からの流出水のｐＨが９.０以上となるようにする。流出水のｐＨが９.０未満の場合、アルカリ凝集装置１におけるカルシウム及びマグネシウムなどの析出および凝集が不十分となり、海水のような硬度が高い被処理水中に溶存しているカルシウムやマグネシウムが過飽和状態のままアルカリ凝集装置１および凝集混和槽２の後段のろ過体に到達することとなる。従って、流出水のｐＨが９.０未満であれば、ろ過体自身、或いは、アルカリ凝集装置とろ過体との間の導水部においてスケールが形成される可能性が高くなり、長時間に亘り継続的に被処理水を前処理することが困難となるからである。 The addition amount of the alkaline agent in the alkali flocculation apparatus 1 is set so that the pH of the effluent water from the alkali flocculation apparatus 1 is 9.0 or more. When the pH of the effluent water is less than 9.0, precipitation and flocculation of calcium and magnesium in the alkali flocculation apparatus 1 become insufficient, and calcium and magnesium dissolved in water to be treated having high hardness such as seawater are supersaturated. The alkali flocculation apparatus 1 and the flocculation / mixing tank 2 reach the subsequent stage filter in the state. Therefore, if the pH of the effluent water is less than 9.0, there is a high possibility that a scale will be formed in the filter itself or in the water conduit between the alkali agglomeration device and the filter, and it will continue for a long time. This is because it becomes difficult to pretreat the water to be treated.
　そして、この前処理方法の一例では、アルカリ凝集装置１でのアルカリ凝集によってｐＨが９．０以上とされた被処理水が凝集混和槽２に流下する。従って、凝集混和槽２では、この環境で凝集効果を発揮する凝集剤が被処理水に添加される。このような凝集剤としては、例えば塩化第二鉄が用いられる。 And in this example of the pretreatment method, the water to be treated whose pH is set to 9.0 or more by the alkali flocculation in the alkali flocculation apparatus 1 flows down into the flocculation mixing tank 2. Therefore, in the flocculation mixing tank 2, a flocculating agent that exhibits a flocculating effect in this environment is added to the water to be treated. As such an aggregating agent, for example, ferric chloride is used.
　凝集剤が添加された被処理水を凝集混和槽２で緩速撹拌すると、アルカリ凝集装置１でのアルカリ凝集によって析出した微細粒子を凝集核とするフロックが形成される。この際、被処理水中の浮遊性物質や有機物などがフロック中に取り込まれる。なお、海水は濁度が低いため、直接凝集剤を注入しても十分な凝集効果は得られない。従って、本発明のように凝集工程の前段でアルカリ凝集を行って凝集核を形成しておくことが有効である。 When the water to be treated to which the flocculant is added is slowly stirred in the flocculation mixing tank 2, flocs are formed in which fine particles precipitated by alkali flocculation in the alkali flocculation apparatus 1 are formed as flocculation nuclei. At this time, floating substances or organic substances in the water to be treated are taken into the floc. In addition, since seawater has low turbidity, a sufficient coagulation effect cannot be obtained even if the coagulant is directly injected. Therefore, it is effective to form aggregated nuclei by performing alkali aggregation before the aggregation process as in the present invention.
　凝集混和槽２を経た被処理水は、耐アルカリ性かつ耐酸性のろ過体３に送られ、膜ろ過される。この耐アルカリ性かつ耐酸性のろ過体３としては、例えば膜孔径が０.１μｍのセラミック製モノリス膜を用いることができる。ここで、ろ過体３の膜形状は必ずしもモノリス膜に限定されるものではなく、平膜であってもチューブラー膜であってもよい。そして、この耐アルカリ性かつ耐酸性のろ過体３によって浮遊性物質及び有機物などが膜分離される。なお、ろ過体３でのろ過により得られる膜ろ過水は、ＳＤＩが３.０程度であり、逆浸透膜に供給することができるものである。 The water to be treated that has passed through the flocculation / mixing tank 2 is sent to the alkali- and acid-resistant filter body 3 and subjected to membrane filtration. As the alkali-resistant and acid-resistant filter body 3, for example, a ceramic monolith membrane having a membrane pore diameter of 0.1 μm can be used. Here, the membrane shape of the filter body 3 is not necessarily limited to the monolith membrane, and may be a flat membrane or a tubular membrane. Then, floating substances and organic substances are membrane-separated by the alkali- and acid-resistant filter 3. In addition, the membrane filtered water obtained by filtration with the filter body 3 has an SDI of about 3.0, and can be supplied to the reverse osmosis membrane.
　耐アルカリ性かつ耐酸性のろ過体３へ流入する流入水は、アルカリ凝集装置１におけるアルカリ凝集工程と、凝集混和槽２における凝集工程とによりある程度硬度が低減されているが、まだスケールを発生させる成分が残存している状態であり、アルカリ性である。従って、上記流入水の膜ろ過によって耐アルカリ性かつ耐酸性のろ過体３のろ過面に炭酸カルシウム等のスケールが形成されることを避けられない。このため、ろ過運転を継続すると、耐アルカリ性かつ耐酸性のろ過体３の膜面には、このスケール形成に由来するものと、凝集混和槽２での塩化第二鉄の添加により形成された凝集物（フロック）に由来するものとがファウリング物質として次第に蓄積する。 The inflowing water flowing into the alkali-resistant and acid-resistant filter 3 has a certain degree of hardness reduced by the alkali flocculation process in the alkali flocculation apparatus 1 and the flocculation process in the flocculation mixing tank 2, but it still generates scale. Is remaining and is alkaline. Therefore, it is inevitable that a scale such as calcium carbonate is formed on the filtration surface of the alkali-resistant and acid-resistant filter body 3 by membrane filtration of the influent water. For this reason, if the filtration operation is continued, the membrane surface of the alkali-resistant and acid-resistant filter body 3 is agglomerated by the addition of ferric chloride in the agglomeration and mixing tank 2 due to this scale formation. Things derived from things (floc) gradually accumulate as fouling substances.
　そこで、耐アルカリ性かつ耐酸性のろ過体３は、ファウリング物質の蓄積による膜差圧の上昇に応じて定期的に酸洗浄される。この酸洗浄では、蓄積したファウリング物質を溶解させて除去する。前記したように、本発明で用いるろ過体３は耐酸性に優れるため、ｐＨ２以下の既知の強酸による酸洗浄を行っても膜劣化がない。従って、ｐＨ２以下の強酸を用いた酸洗浄により短時間で膜ファウリングを解消することができる。このように本発明によれば、膜差圧の上昇を速やかに回復しながら長期間にわたり安定した運転が可能である。即ち、本発明によれば、長期間、前処理水の水質が悪化することがない。 Therefore, the alkali-resistant and acid-resistant filter body 3 is periodically acid-washed according to the increase in the membrane differential pressure due to the accumulation of fouling substances. In this acid cleaning, accumulated fouling substances are dissolved and removed. As described above, since the filter body 3 used in the present invention is excellent in acid resistance, there is no film deterioration even when acid cleaning with a known strong acid having a pH of 2 or less is performed. Therefore, membrane fouling can be eliminated in a short time by acid cleaning using a strong acid having a pH of 2 or lower. Thus, according to the present invention, stable operation over a long period of time is possible while quickly recovering the increase in membrane differential pressure. That is, according to the present invention, the quality of the pretreated water does not deteriorate for a long time.
　本発明にかかる被処理水の逆浸透膜分離のための前処理方法に用いる前処理装置の第１実施形態を図２に示す。 FIG. 2 shows a first embodiment of a pretreatment apparatus used in a pretreatment method for reverse osmosis membrane separation of water to be treated according to the present invention.
　この第１実施形態の前処理装置は、凝集分離装置１０と、ろ過体２２とを備える。そして、この前処理装置で処理された水（前処理水）は、図示しない逆浸透膜でろ過されて透過水と濃縮水とに分離される。 The pretreatment device of the first embodiment includes a flocculation / separation device 10 and a filter body 22. And the water (pretreatment water) processed with this pretreatment apparatus is filtered with the reverse osmosis membrane which is not illustrated, and is separated into permeated water and concentrated water.
　ここで、この前処理装置で処理される被処理水としては、例えば海水やかん水等の全硬度濃度が３００ｍｇ／Ｌ（ＣａＣＯ３換算濃度）以上の高硬度水が挙げられる。なお、全硬度濃度は、ＪＩＳ　Ｋ０１０１に準拠して、ＩＣＰ発光分光分析法を用いて水中のカルシウムおよびマグネシウム濃度の総和を算出することにより求めることができる。 Here, as the water to be treated to be treated by this pretreatment device, for example, high-hardness water having a total hardness concentration of 300 mg / L (CaCO 3 equivalent concentration) or more, such as seawater or brine. The total hardness concentration can be determined by calculating the sum of calcium and magnesium concentrations in water using ICP emission spectroscopic analysis in accordance with JIS K0101.
　凝集分離装置１０は円筒状で、アルカリ凝集槽１１と、アルカリ凝集槽１１の上方に設けられた凝集沈降槽１２と、アルカリ凝集槽１１と凝集沈降槽１２との間を被処理水が流通可能なように仕切る仕切り板１５とを備える。なお、本実施形態において、アルカリ凝集槽１１は上記一例のアルカリ凝集装置１に相当し、凝集沈降槽１２は上記一例の凝集混和槽２に相当する。 The aggregating and separating apparatus 10 has a cylindrical shape, and the water to be treated can flow between the alkali aggregating tank 11, the aggregating and sedimenting tank 12 provided above the alkali aggregating tank 11, and the alkali aggregating tank 11 and the agglomerating and sedimenting tank 12. And a partition plate 15 for partitioning. In the present embodiment, the alkali flocculation tank 11 corresponds to the alkali flocculation apparatus 1 of the above example, and the flocculation settling tank 12 corresponds to the flocculation mixing tank 2 of the above example.
　アルカリ凝集槽１１には、被処理水注入手段としての被処理水流入口１３と、アルカリ剤注入手段としてのアルカリ注入口１４とが設けられている。そして、アルカリ凝集槽１１では、被処理水流入口１３から流入した被処理水と、アルカリ注入口１４を介して注入されたアルカリ剤とが接触し、上向流で水流撹拌される。すなわち、上向流式の接触手法が実現されている。従って、アルカリ凝集槽１１では、被処理水のｐＨが上昇して、被処理水中のカルシウム及びマグネシウムが白濁物質（炭酸塩または水酸化物）として析出する。ここで、アルカリ剤としては、例えば水酸化ナトリウム、炭酸ナトリウム等を用いることができる。また、アルカリ剤の注入量は、凝集分離装置１０から流出する水のｐＨが９．０以上となるように既知の手段で調整することができる。なお、水流撹拌とは、撹拌機等を用いて機械的に撹拌するのではなく、装置に流入する水の流れ（水流）自体を用いて撹拌することを指す。具体的には、槽内の水理学的な乱れの指標であるレイノルズ数が１００００以上となるように、被処理水およびアルカリ剤の設計流入量に対して槽の断面積を設定することで、水流撹拌を実現することができる。このようにすれば、撹拌装置を用いない簡易な構成の装置で高硬度原水膜ろ過の前処理を行うことができる。 The alkali agglomeration tank 11 is provided with a treated water inlet 13 as treated water injection means and an alkaline inlet 14 as alkaline agent injection means. In the alkali agglomeration tank 11, the water to be treated that has flowed from the water to be treated inlet 13 and the alkali agent injected through the alkali inlet 14 come into contact with each other, and the water is stirred in an upward flow. That is, an upward flow contact method is realized. Therefore, in the alkali flocculation tank 11, the pH of the water to be treated is increased, and calcium and magnesium in the water to be treated are precipitated as white turbid substances (carbonates or hydroxides). Here, as an alkaline agent, sodium hydroxide, sodium carbonate, etc. can be used, for example. Moreover, the injection amount of the alkaline agent can be adjusted by a known means so that the pH of the water flowing out from the coagulation / separation apparatus 10 becomes 9.0 or more. In addition, water flow stirring refers to stirring using the flow (water flow) itself of water flowing into the apparatus, not mechanical stirring using a stirrer or the like. Specifically, by setting the cross-sectional area of the tank with respect to the design inflow of the water to be treated and the alkaline agent so that the Reynolds number, which is an indicator of hydraulic disturbance in the tank, is 10,000 or more, Water agitation can be realized. If it does in this way, the pre-process of high hardness raw | natural water membrane filtration can be performed with the apparatus of a simple structure which does not use a stirring apparatus.
　仕切り板１５は、凝集沈降槽１２側に突出する複数のノズル１６を有している。そして、ノズル１６を通って、被処理水と、アルカリ凝集槽１１で析出した白濁物質とがアルカリ凝集槽１１から凝集沈降槽１２へと流れる。 The partition plate 15 has a plurality of nozzles 16 protruding toward the coagulation sedimentation tank 12 side. Then, the water to be treated and the cloudy substance precipitated in the alkali coagulation tank 11 flow from the alkali coagulation tank 11 to the coagulation sedimentation tank 12 through the nozzle 16.
　凝集沈降槽１２の上部には、凝集剤注入手段としての凝集剤注入口１８と、被処理水流出口と、撹拌機２１とが設けられており、凝集沈降槽１２の下部には、排泥手段としての汚泥排出口２０が設けられている。そして、この凝集沈降槽１２の上部では、アルカリ凝集槽１１から流入した被処理水および白濁物質の混合物に対し、塩化第二鉄などの凝集剤が、例えば濃度が１～６ｍｇ／Ｌ（鉄換算）となるように添加、混合される。従って、アルカリ凝集槽１１から流入した白濁物質は、凝集沈降槽１２の下部から上部まで流れ、上部で添加された凝集剤と接触してフロックを形成するが、一部の白濁物質は上部まで流れる間に沈降分離する。なお、このフロック形成過程においては、被処理水中に含まれている浮遊性物質及び有機物もフロック中に取り込まれる。 In the upper part of the coagulation sedimentation tank 12, a coagulant injection port 18 as a coagulant injection means, a water outlet to be treated, and a stirrer 21 are provided. The sludge discharge port 20 is provided. In the upper part of the coagulation sedimentation tank 12, a coagulant such as ferric chloride with respect to the mixture of the water to be treated and the cloudy substance flowing from the alkali coagulation tank 11 has a concentration of, for example, 1 to 6 mg / L (iron equivalent) ) And mixed. Therefore, the white turbid substance flowing in from the alkali flocculation tank 11 flows from the lower part to the upper part of the flocculation settling tank 12 and comes into contact with the flocculant added at the upper part to form a floc, but a part of the white turbid substance flows to the upper part. Settling in between. In this floc formation process, floating substances and organic substances contained in the water to be treated are also taken into the floc.
　凝集剤の添加により形成したフロックの一部は凝集沈降槽１２内を沈降し、凝集沈降槽１２の下部から上部まで流れる間に沈降した白濁物質と共に仕切り板１５上の集積部１７に集積される。そして、集積されたフロックおよび白濁物質は、排泥手段としての汚泥排出口２０より定期的に引き抜かれる。具体的には、汚泥排出口２０の後段側に設けた仕切り弁（図示せず）の間欠的な開閉、或いは、連続的な開放により適宜排出することができる。なお、排泥は、水頭差を用いて行ってもよいし、排水ポンプを用いて行ってもよい。 A part of the floc formed by adding the flocculant settles in the flocculent sedimentation tank 12 and accumulates in the accumulating portion 17 on the partition plate 15 together with the cloudy substance that settles while flowing from the lower part to the upper part of the flocculent sedimentation tank 12. . Then, the accumulated floc and cloudy substance are periodically withdrawn from the sludge discharge port 20 as a mud discharge means. Specifically, it can be appropriately discharged by intermittently opening or closing a gate valve (not shown) provided on the rear stage side of the sludge discharge port 20 or by continuous opening. In addition, waste mud may be performed using a water head difference, and may be performed using a drainage pump.
　そして、凝集沈降槽１２の上部の被処理水流出口から流出した被処理水およびフロックは、凝集分離装置１０の後段に設けられたろ過体２２でろ過される。従って、凝集分離装置１０での沈降分離およびろ過体２２でのろ過により、スケールを形成する可能性のある成分（カルシウムおよびマグネシウム）、浮遊性物質及び有機物を除去した前処理水を得ることができる。なお、ろ過体２２としては、例えば、耐アルカリ性且つ耐酸性の精密ろ過膜もしくは限外ろ過膜を用いることができる。 And the to-be-processed water and the floc which flowed out from the to-be-processed water outflow port of the upper part of the coagulation sedimentation tank 12 are filtered with the filter body 22 provided in the back | latter stage of the coagulation-separation apparatus 10. FIG. Therefore, pretreatment water from which components (calcium and magnesium), floatable substances and organic substances that may form a scale can be obtained by sedimentation separation in the flocculation separation apparatus 10 and filtration through the filter 22 can be obtained. . In addition, as the filter body 22, for example, an alkali-resistant and acid-resistant microfiltration membrane or an ultrafiltration membrane can be used.
　次に、本発明にかかる被処理水の逆浸透膜分離のための前処理方法に用いる前処理装置の第２実施形態を図３に示す。 Next, FIG. 3 shows a second embodiment of the pretreatment apparatus used in the pretreatment method for reverse osmosis membrane separation of water to be treated according to the present invention.
　この第２実施形態の前処理装置は、アルカリ凝集槽と凝集混和槽とを有する凝集分離槽３０と、ろ過体３６とを備える。そして、この前処理装置で処理された水（前処理水）は、図示しない逆浸透膜でろ過されて透過水と濃縮水とに分離される。 The pretreatment device of the second embodiment includes a flocculation / separation tank 30 having an alkali flocculation tank and a flocculation / mixing tank, and a filter body 36. And the water (pretreatment water) processed with this pretreatment apparatus is filtered with the reverse osmosis membrane which is not illustrated, and is separated into permeated water and concentrated water.
　凝集分離槽３０は、被処理水貯槽３１と、アルカリ凝集槽３２と、凝集混和槽３３とからなり、被処理水貯槽３１とアルカリ凝集槽３２、アルカリ凝集槽３２と凝集混和槽３３はそれぞれ下部で連通している。従って、凝集分離槽３０に流入した被処理水は、被処理水貯槽３１に貯水された後、被処理水貯槽３１の下部からアルカリ凝集槽３２へと流入する。なお、本実施形態において、アルカリ凝集槽３２は上記一例のアルカリ凝集装置１に相当し、凝集混和槽３３は上記一例の凝集混和槽２に相当する。 The flocculation / separation tank 30 includes a treated water storage tank 31, an alkali flocculation tank 32, and an agglomeration mixing tank 33. It communicates with. Therefore, the water to be treated that has flowed into the flocculation / separation tank 30 is stored in the water to be treated 31 and then flows from the lower part of the water to be treated 31 into the alkali flocculation tank 32. In the present embodiment, the alkali flocculation tank 32 corresponds to the alkali flocculation apparatus 1 of the above example, and the flocculation mixing tank 33 corresponds to the flocculation / mixing tank 2 of the above example.
　本実施形態におけるアルカリ凝集槽３２は、攪拌機３４を備える。そして、アルカリ凝集槽３２では、例えば水酸化ナトリウム等のアルカリ剤が被処理水に添加され、撹拌機３４で被処理水およびアルカリ剤が混合される。これにより、被処理水のｐＨが上昇して、被処理水中のカルシウム及びマグネシウムが白濁物質（炭酸塩または水酸化物）として析出する。ここで、アルカリ剤の注入量は、凝集分離槽３０から流出する水のｐＨが９．０以上となるように既知の手段で調整することができる。 The alkali flocculation tank 32 in this embodiment includes a stirrer 34. In the alkali agglomeration tank 32, for example, an alkali agent such as sodium hydroxide is added to the water to be treated, and the water to be treated and the alkali agent are mixed by the stirrer 34. Thereby, pH of to-be-processed water rises and calcium and magnesium in to-be-processed water precipitate as a cloudy substance (carbonate or hydroxide). Here, the injection amount of the alkaline agent can be adjusted by a known means so that the pH of the water flowing out from the coagulation / separation tank 30 becomes 9.0 or more.
　そして、アルカリ凝集槽３２で析出した白濁物質の一部はアルカリ凝集槽３２内で沈降して分離される。一方、アルカリ凝集槽３２内で沈降しなかった白濁物質と、被処理水とは、アルカリ凝集槽３２の下部から凝集混和槽３３へと流入する。 Then, a part of the cloudy substance precipitated in the alkali flocculation tank 32 is settled and separated in the alkali flocculation tank 32. On the other hand, the cloudy substance that has not settled in the alkali coagulation tank 32 and the water to be treated flow into the coagulation mixing tank 33 from the lower part of the alkali coagulation tank 32.
　凝集混和槽３３では、アルカリ凝集槽３２から流入した被処理水および白濁物質に対し、塩化第二鉄などの凝集剤が添加され、撹拌機３５で被処理水、白濁物質および凝集剤が混合される。そして、白濁物質は凝集剤の添加により凝集してフロックを形成する。なお、このフロック形成過程においては、被処理水中に含まれている浮遊性物質及び有機物もフロック中に取り込まれる。 In the agglomeration mixing tank 33, a coagulant such as ferric chloride is added to the water to be treated and the cloudy substance flowing from the alkali coagulation tank 32, and the water to be treated, the cloudy substance and the flocculant are mixed by the stirrer 35. The The cloudy substance aggregates to form flocs by the addition of the flocculant. In this floc formation process, floating substances and organic substances contained in the water to be treated are also taken into the floc.
　そして、凝集混和槽３３から流出した被処理水およびフロックは、凝集分離槽３０の後段に設けられたろ過体３６でろ過される。このように、アルカリ凝集槽３２での沈降分離およびろ過体３６でのろ過により、スケールを形成する可能性のある成分（カルシウムおよびマグネシウム）、浮遊性物質及び有機物を除去した前処理水を得ることができる。なお、ろ過体３６としては、例えばセラミック製の膜を用いることができる。 And the to-be-processed water and floc which flowed out from the coagulation mixing tank 33 are filtered with the filter body 36 provided in the back | latter stage of the coagulation separation tank 30. FIG. Thus, pretreatment water from which components (calcium and magnesium), floatable substances and organic substances that may form scales are removed is obtained by sedimentation separation in the alkali coagulation tank 32 and filtration in the filter body 36. Can do. As the filter body 36, for example, a ceramic membrane can be used.
　ここで、上述した第１実施形態および第２実施形態の前処理装置では、ろ過体として耐酸性を有する膜を使用しているので、ろ過体が目詰まりを起こした場合には、ｐＨ２以下の強酸で洗浄することができる。即ち、第１実施形態および第２実施形態の前処理装置では、短時間でファウリングを解消することができる。 Here, in the pretreatment apparatus of the first embodiment and the second embodiment described above, a membrane having acid resistance is used as the filter body. Therefore, when the filter body is clogged, the pH is 2 or less. Can be washed with strong acid. That is, in the pretreatment devices of the first and second embodiments, fouling can be eliminated in a short time.
［実施例１］
　図２に示す前処理装置を用いてｐＨ８前後の海水を処理した。具体的には、図２の凝集分離装置１０に海水を線速度１０ｍ／ｈｒ以上の上向流で流すと共に、海水にアルカリ剤としてＮａＯＨを添加した。そして、アルカリ剤添加後の海水のｐＨが９．０以上となる条件でアルカリ凝集を行った。その後、アルカリ凝集槽１１を経て凝集沈降槽１２に導入された海水（全溶解成分(ＴＤＳ)濃度３．５％）に、凝集剤として塩化第二鉄を１～６ｍｇ／Ｌ（鉄の換算値として）の割合で添加した。更に、凝集剤を添加した海水を膜孔径が０．１μｍのセラミック製モノリス膜３（精密ろ過セラミック膜）でろ過した。その際のろ過流束は６～８ｍ３／ｍ２／日であり、２０００時間後も１００ＫＰａを超える差圧の上昇はみられなかった。なお、ＴＤＳは、試料（海水）を１１０℃で熱して水分を取り除いた際の残留物の重量を計測することにより求めることができる。 [Example 1]
Seawater having a pH of around 8 was treated using the pretreatment apparatus shown in FIG. Specifically, seawater was caused to flow through the flocculation / separation apparatus 10 in FIG. 2 in an upward flow with a linear velocity of 10 m / hr or more, and NaOH was added to the seawater as an alkaline agent. And the alkali aggregation was performed on the conditions from which pH of the seawater after alkali agent addition was set to 9.0 or more. Thereafter, ferric chloride as a coagulant is 1 to 6 mg / L (converted value of iron) into seawater (total dissolved component (TDS) concentration 3.5%) introduced into the coagulation sedimentation tank 12 through the alkali coagulation tank 11. As)). Furthermore, the seawater to which the flocculant was added was filtered through a ceramic monolith membrane 3 (microfiltration ceramic membrane) having a membrane pore diameter of 0.1 μm. The filtration flux at that time was 6 to 8 m 3 / m 2 / day, and no increase in the differential pressure exceeding 100 KPa was observed even after 2000 hours. The TDS can be determined by measuring the weight of the residue when the sample (seawater) is heated at 110 ° C. to remove moisture.
［実施例２］
　図３に示す装置を用い、アルカリ凝集操作後のｐＨを変化させて海水を処理した。具体的には、海水を膜ろ過流束７ｍ３／ｍ２／日で処理するにあたり、アルカリ凝集後のｐＨを７．８にした場合と、９．５にした場合について膜間差圧の変化を測定した。なお、凝集剤には実施例１と同様のものを用いた。また、膜間差圧は膜の一次側と二次側の操作圧力を圧力計で測定し、その差を算出することにより求めた。結果を図４に示す。 [Example 2]
Using the apparatus shown in FIG. 3, seawater was treated by changing the pH after the alkali flocculation operation. Specifically, when seawater is treated with a membrane filtration flux of 7 m 3 / m 2 / day, the change in transmembrane pressure difference between the case where the pH after alkali aggregation is 7.8 and the case where it is 9.5. Was measured. The same flocculant as that used in Example 1 was used. The transmembrane pressure difference was determined by measuring the operating pressure on the primary side and the secondary side of the membrane with a pressure gauge and calculating the difference. The results are shown in FIG.
　その結果、ｐＨ９．５とした方が膜間差圧の上昇が少なく、前処理を長時間連続して行えることがわかった。 As a result, it was found that when the pH was set to 9.5, the increase in transmembrane pressure difference was small and the pretreatment could be performed continuously for a long time.

Claims (5)

  1. 　被処理水にアルカリ剤を添加してｐＨを９．０以上に調整することにより、前記被処理水に溶解しておりスケールを形成する可能性のある成分を非溶解性物質として析出させ、そのアルカリ凝集操作によって生じた析出物の一部を沈降分離した後に、ｐＨ９．０以上の環境を維持したまま凝集剤を添加して残存する析出物を凝集核とするフロックを形成させたうえ、耐アルカリ性かつ耐酸性のろ過体を用いてろ過を行い、スケールを形成する可能性のある成分、浮遊性物質及び有機物を除去することを特徴とする被処理水の逆浸透膜による分離のための前処理方法。 By adjusting the pH to 9.0 or more by adding an alkali agent to the water to be treated, the components that are dissolved in the water to be treated and that may form scales are precipitated as insoluble substances, After a part of the precipitate produced by the alkali agglomeration operation is settled and separated, a floc is formed by adding a flocculant while maintaining an environment of pH 9.0 or higher and using the remaining precipitate as an agglomerated nucleus. Before separation by reverse osmosis membrane of water to be treated, characterized by removing components, floatable substances and organic substances that may form scale by performing filtration using an alkaline and acid-resistant filter. Processing method.
  2. 　前記耐アルカリ性かつ耐酸性のろ過体が、セラミック製ろ過体であって、６ｍ３／ｍ２／日以上の流束でろ過することを特徴とする請求項１記載の被処理水の逆浸透膜による分離のための前処理方法。 The reverse osmosis membrane of water to be treated according to claim 1, wherein the alkali-resistant and acid-resistant filter body is a ceramic filter body and is filtered with a flux of 6 m 3 / m 2 / day or more. Pretreatment method for separation by.
  3. 　前記耐アルカリ性かつ耐酸性のろ過体の膜差圧上昇を伴ったファウリングに対して、ｐＨ２以下の酸で前記ろ過体の酸洗浄を行うことを特徴とする請求項1または請求項２記載の被処理水の逆浸透膜による分離のための前処理方法。 The acid cleaning of the filter according to claim 1 or 2, wherein the filter is acid-washed with an acid having a pH of 2 or less against fouling accompanied by an increase in membrane differential pressure of the alkali-resistant and acid-resistant filter. A pretreatment method for separation by reverse osmosis membrane of water to be treated.
  4. 　前記凝集剤として塩化第二鉄を用いることを特徴とする請求項1または請求項２記載の被処理水の逆浸透膜による分離のための前処理方法。 3. A pretreatment method for separating water to be treated by a reverse osmosis membrane according to claim 1 or 2, wherein ferric chloride is used as the flocculant.
  5. 　前記アルカリ凝集操作を上向流式の接触手法を用いて行うことを特徴とする請求項1または請求項２記載の被処理水の逆浸透膜による分離のための前処理方法。 3. The pretreatment method for separating water to be treated by a reverse osmosis membrane according to claim 1 or 2, wherein the alkali agglomeration operation is performed using an upward flow contact method.
PCT/JP2009/054463 2008-03-24 2009-03-09 Method of pretreatment for separation with reverse osmosis membrane of water to be treated WO2009119300A1 (en)

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