Abstract: The present invention is a method for operating a demineralization apparatus provided with a plurality of demineralizing lines arranged in parallel and having demineralizers, the method comprising passing through some of the demineralizing lines water to be treated to produce demineralized water while passing through another demineralizing line(s) dilute water from a dilute water tank to perform washing of the line(s), and returning water used for said washing back to the dilute water tank, and being characterized by, when the water quality of the dilute water is on the high salts concentration side past a predefined value, discharging part of the dilute water so as to let said part join the water to be treated and providing a new supply of dilute water for replenishment.

Abstract: The purpose of the present invention is to provide a technique whereby it becomes possible to operate for a longer period of time in an aqueous system equipped with a membrane separation apparatus. The present invention can provide a membrane separation method, the method comprising containing a combined-chlorine-based oxidizing agent to water of interest, and allowing the water of interest which contains the combined-chlorine-based oxidizing agent to pass through a membrane separation apparatus, in which the water of interest which contains the combined-chlorine-based oxidizing agent has a Free 300-second value of 0.036 mg/L-Cl2 or more wherein the Free 300-second value is a result of the measurement of a chlorine concentration after 300 seconds using a free chlorine measurement reagent.

Abstract: Multiple chemical dosing levels of differing chemical dosages are set. When control is initiated, chemical dosing is started at the level with the highest chemical dosage. Each time a sampling period S passes, the rate of increase in the pressure difference of an RO system is compared with a threshold value A. When the rate of increase is at or below the threshold value A, the chemical dosage is reduced to the level that is one step lower. When the rate of increase is greater than the threshold value A, the chemical dosage is increased to the level that is one step higher.

Abstract: Water discharged from a circulating cooling water system is treated by a water recovery system including a clarification equipment and an RO membrane, and treated water is returned to the circulating cooling water system. A dispersant is added to the circulating cooling water system for dispersing scale components. The dispersant includes a polymer having a carboxyl group and having a weight average molecular weight of 5,000 or less, and permeates through the clarification equipment. The polymer having a carboxyl group and having a weight average molecular weight of 5,000 or less permeates through the clarification equipment, and performs as a scale dispersing agent for the RO membrane, preventing precipitation of scale. Since the polymer intrinsically has an anticorrosion effect, it becomes unnecessary to add a phosphoric acid compound to the cooling water system as an anticorrosion agent, or the required amount of the compound to be added can be reduced.

Abstract: The invention provides cleaning agents, cleaning liquids and cleaning methods that effectively remove contaminants which are impossible to remove sufficiently with conventional cleaning liquids at the occurrence of a decrease in performances such as permeation flux and salt rejection rate due to contamination of permeable membranes, in particular aromatic polyamide RO membranes used in water treatment. Permeable membranes are cleaned with a cleaning liquid which is an aqueous solution including a chloramine compound and an alkali agent and having a pH of 10 or above. The chloramine compound is preferably one obtained by mixing a compound having a primary amino group with hypochlorous acid and/or a hypochlorite.

Abstract: Provide is a reverse osmosis membrane device that is capable of treating raw water containing membrane-fouling substance in large quantities, such as MBR-treated water, in a stable manner while preventing decreases in permeate flow rate, and a method for operating thereof. A method for operating a reverse osmosis membrane device that treats raw water containing high-molecular-weight organic matter, wherein the raw water contains high-molecular-weight organic matter having a molecular weight of 10,000 or more at a concentration of 0.01 ppm or more, wherein the reverse osmosis membrane device is equipped with a spiral-type reverse osmosis membrane element that has a membrane surface area satisfying the below formula (1), and wherein the reverse osmosis membrane device is operated at a permeate flux of 0.6 m/d or less: membrane surface area(m2)?n2×(11/16)??(1) wherein n represents a diameter (inches) of the reverse osmosis membrane element.

Abstract: Provided are reverse-osmosis-membrane device capable of treating raw water including a large amount of membrane foulants, such as MBR-treated water, with stability while preventing a reduction in the amount of permeate, and a method for operating the reverse-osmosis-membrane device. The raw water includes a high-molecular organic substance having a molecular weight of 10,000 or more at a concentration of 0.01 ppm or more. The reverse-osmosis-membrane device includes a reverse-osmosis-membrane element including a membrane unit, the membrane unit including a reverse osmosis membrane having a thickness of 0.1 mm or less, a feed spacer disposed on a surface of the reverse osmosis membrane, and a permeate spacer disposed on the other surface of the reverse osmosis membrane. The reverse-osmosis-membrane device is operated at a permeation flux of 0.6 m/d or less.

Abstract: To provide a method for improving a rejection rate of an RO membrane, which further improves the stability of removal performance (rejection rate) and flux stability (sustainability of contamination resistance). In a method for improving a rejection rate of an RO membrane, including a step of allowing an aqueous solution containing a polyphenol to pass through an RO membrane, the method further includes a step of allowing an aqueous solution containing at least one type selected from the group consisting of a modified poly(vinyl alcohol), a high molecular polysaccharide, and a poly(amino acid) to pass through the RO membrane. The method preferably further includes a step of allowing an aqueous solution containing an organic compound having an amino group and having a molecular weight of 1,000 or less to pass through the RO membrane.

Abstract: Water discharged from a circulating cooling water system is treated by a water recovery system including a clarification equipment and an RO membrane, and treated water is returned to the circulating cooling water system. A dispersant is added to the circulating cooling water system for dispersing scale components. The dispersant includes a polymer having a carboxyl group and having a weight average molecular weight of 5,000 or less, and permeates through the clarification equipment. The polymer having a carboxyl group and having a weight average molecular weight of 5,000 or less permeates through the clarification equipment, and performs as a scale dispersing agent for the RO membrane, preventing precipitation of scale. Since the polymer intrinsically has an anticorrosion effect, it becomes unnecessary to add a phosphoric acid compound to the cooling water system as an anticorrosion agent, or the required amount of the compound to be added can be reduced.

Abstract: Provided are reverse-osmosis-membrane device capable of treating raw water including a large amount of membrane foulants, such as MBR-treated water, with stability while preventing a reduction in the amount of permeate, and a method for operating the reverse-osmosis-membrane device. The raw water includes a high-molecular organic substance having a molecular weight of 10,000 or more at a concentration of 0.01 ppm or more. The reverse-osmosis-membrane device includes a reverse-osmosis-membrane element including a membrane unit, the membrane unit including a reverse osmosis membrane having a thickness of 0.1 mm or less, a feed spacer disposed on a surface of the reverse osmosis membrane, and a permeate spacer disposed on the other surface of the reverse osmosis membrane. The reverse-osmosis-membrane device is operated at a permeation flux of 0.6 m/d or less.

Abstract: A method capable of effectively improving a rejection of a reverse osmosis membrane without remarkably reducing a permeation flux, even if the membrane is seriously degraded. An aqueous solution containing a first organic compound having a molecular weight of less than 200, a second organic compound having a molecular weight of 200 to less than 500, and a third organic compound having a molecular weight of 500 or more is passed through the reverse osmosis membrane. The first organic compound is preferably an amino acid or an amino acid derivative. The total concentration of the first organic compound and the second organic compound and the concentration of the third organic compound are each preferably 1 to 500 mg/L.

Abstract: Provide is a reverse osmosis membrane device that is capable of treating raw water containing membrane-fouling substance in large quantities, such as MBR-treated water, in a stable manner while preventing decreases in permeate flow rate, and a method for operating thereof. A method for operating a reverse osmosis membrane device that treats raw water containing high-molecular-weight organic matter, wherein the raw water contains high-molecular-weight organic matter having a molecular weight of 10,000 or more at a concentration of 0.01 ppm or more, wherein the reverse osmosis membrane device is equipped with a spiral-type reverse osmosis membrane element that has a membrane surface area satisfying the below formula (1), and wherein the reverse osmosis membrane device is operated at a permeate flux of 0.6 m/d or less: membrane surface area (m2)?n2×(11/16)??(1) wherein n represents a diameter (inches) of the reverse osmosis membrane element.

Abstract: A quality of treated water is improved without loss of stability in multi-stage reverse osmosis membrane treatment. Raw water in a raw water tank 1 is fed to a first-stage reverse osmosis membrane unit 3 by compression with a first pump 2, and concentrated water is discharged while permeated water is introduced into an intermediate tank 5 through a piping 4. The water in the intermediate tank 5 is fed to a second-stage reverse osmosis membrane unit 7 by compression with a second pump 6, and permeated water is taken out through a piping 8 while concentrated water is returned to the raw water tank 1 through a piping 9. The thickness of the raw water spacer of the reverse osmosis membrane units is more than 0.6 mm for the first stage and is 0.6 mm or less for the second stage.

Abstract: To provide a method for improving a rejection rate of an RO membrane, which further improves the stability of removal performance (rejection rate) and flux stability (sustainability of contamination resistance). In a method for improving a rejection rate of an RO membrane, including a step of allowing an aqueous solution containing a polyphenol to pass through an RO membrane, the method further includes a step of allowing an aqueous solution containing at least one type selected from the group consisting of a modified poly(vinyl alcohol), a high molecular polysaccharide, and a poly(amino acid) to pass through the RO membrane. The method preferably further includes a step of allowing an aqueous solution containing an organic compound having an amino group and having a molecular weight of 1,000 or less to pass through the RO membrane.

Abstract: Disclosed are a method for further purifying ultrapure water, according to which any impurities in ultrapure water can be stably removed to a high degree within a small space over a prolonged period; and an apparatus therefor. Ultrapure water introduced into an ultrapure-water purifying apparatus 10 passes through an ion exchange resin layer 5 in a lower chamber 1a. During this process, metal ions, for example, in the ultrapure water are removed by the ion exchange resin. The ultrapure water then passes through a perforated plate 4, flows into an upper chamber 1b, and permeates an ion exchange filter 6. During this process, metal ions and other impurities remaining unremoved by the ion exchange resin layer 5 are removed. Specifically, metal ions are removed to a certain extent by the ion exchange resin, so that it is enough for the ion exchange filter provided downstream thereof to remove an extremely small amount of metal ions.

Abstract: The invention provides cleaning agents, cleaning liquids and cleaning methods that effectively remove contaminants which are impossible to remove sufficiently with conventional cleaning liquids at the occurrence of a decrease in performances such as permeation flux and salt rejection rate due to contamination of permeable membranes, in particular aromatic polyamide RO membranes used in water treatment. Permeable membranes are cleaned with a cleaning liquid which is an aqueous solution including a chloramine compound and an alkali agent and having a pH of 10 or above. The chloramine compound is preferably one obtained by mixing a compound having a primary amino group with hypochlorous acid and/or a hypochlorite.

Abstract: A method capable of effectively improving a rejection of a reverse osmosis membrane without remarkably reducing a permeation flux, even if the membrane is seriously degraded. An aqueous solution containing a first organic compound having a molecular weight of less than 200, a second organic compound having a molecular weight of 200 to less than 500, and a third organic compound having a molecular weight of 500 or more is passed through the reverse osmosis membrane. The first organic compound is preferably an amino acid or an amino acid derivative. The total concentration of the first organic compound and the second organic compound and the concentration of the third organic compound are each preferably 1 to 500 mg/L.

Abstract: An agent for increasing the rejection with a permeable membrane which comprises an ionic macromolecule having a weight-average molecular weight of 100,000 or greater; a process for increasing the rejection with a permeable membrane which comprises treating a permeable membrane with the agent; a permeable membrane which is treated in accordance with the process; and a process for water treatment which comprises using the permeable membrane are disclosed. By using the above agent, an increased rejection of inorganic electrolytes and organic compounds soluble in water can be maintained for a long time easily and safely at the location of the use of the membrane without extreme decrease in the flux of permeation in the membrane separation using a selective permeable membrane such as a nano filtration membrane and a reverse osmosis membrane.

Abstract: This invention provides a method for improving the blocking rate of a permeable membrane, which can reduce a lowering in permeation flux of the permeable membrane to improve the blocking rate, particularly against organic matter, and thus to realize a high organic matter removing effect and stable treatment, and a permeable membrane, a permeable membrane treatment method, and a permeable membrane apparatus. A blocking rate improving agent of a hydrophilic polymer free from a hydrophobic group having 8 or more carbon atoms is supplied to a primary side of a permeable membrane module to deposit the blocking rate improving agent onto the permeable membrane and thus to treat the permeable membrane with the blocking rate improving agent.

Abstract: Disclosed are a method for further purifying ultrapure water, according to which any impurities in ultrapure water can be stably removed to a high degree within a small space over a prolonged period; and an apparatus therefor. Ultrapure water introduced into an ultrapure-water purifying apparatus 10 passes through an ion exchange resin layer 5 in a lower chamber 1a. During this process, metal ions, for example, in the ultrapure water are removed by the ion exchange resin. The ultrapure water then passes through a perforated plate 4, flows into an upper chamber 1b, and permeates an ion exchange filter 6. During this process, metal ions and other impurities remaining unremoved by the ion exchange resin layer 5 are removed. Specifically, metal ions are removed to a certain extent by the ion exchange resin, so that it is enough for the ion exchange filter provided downstream thereof to remove an extremely small amount of metal ions.