Abstract: A method for managing an operation of a reverse osmosis membrane device, includes managing the operation of the reverse osmosis membrane device based on an aluminum ion concentration and/or an iron ion concentration of a feed water and/or a concentrated water of the reverse osmosis membrane device. Any one or more of suitability of a raw water as the feed water, a water temperature of the feed water, a concentration ratio (recovery rate), a pressure (feed water supply pressure, concentrated water pressure, or treated water pressure of the reverse osmosis membrane), an amount of the concentrated water, a continuous operation period, a washing time, a wash frequency, and a timing of replacement of the reverse osmosis membrane are managed based on the aluminum ion concentration and/or the iron ion concentration of the feed water and/or the concentrated water.

Abstract: A method for treating an etching solution in order to circulate and reuse an etching solution used in etching treatment of silicon includes (1) selectively removing multivalent ions having a valence of two or more, or (2) removing multivalent ions having a valence of two or more, 20-50% of alkali metal ions having a valence of one relative to a total amount of the alkali metal ions, and hydroxide ions, through a membrane separation unit comprising a nanofiltration membrane. A permeated solution of the membrane separation unit is circulated to the etching bath.

Abstract: The formation of scale in a reverse osmosis membrane apparatus is reduced at low water temperatures without the necessity of pH adjustment or addition of a scale dispersant to continue a consistent operation for a long period of time. The operation of a reverse osmosis membrane apparatus is controlled on the basis of the concentration of aluminum ions and/or iron ions in the feed to the reverse osmosis membrane apparatus and/or the concentrate from the reverse osmosis membrane apparatus. Not only silica but also aluminum ions and iron ions that are also present in the water significantly affect the reduction in the flux of a reverse osmosis membrane which is caused by silica scale. It is necessary to appropriately control the concentration of aluminum ions and/or iron ions in the feed and/or the concentrate to consistently operate a reverse osmosis membrane apparatus for a long period of time.

Abstract: A method in which an anode chamber and a cathode chamber are separated by a cation exchange membrane, an acid solution containing metal ions is introduced into the anode chamber, a cathode solution is introduced into the cathode chamber, and a current is applied across the anode and the cathode, whereby the metal ions in the solution in the anode chamber pass through the cation exchange membrane, move into the cathode solution, and precipitate as metal onto the cathode, wherein there are minimal instances where electrodeposition is impossible or the electrodeposition rate decreases. Pre-adding a salt of the acid contained in the acid solution makes it possible to suppress concentration-diffusion of the acid from the acid solution. Adding a salt of the acid into the cathode chamber makes it possible to reduce the impressed voltage, reduce the amount of hydrogen generated on the cathode, and reduce the amount of power.

Abstract: A method for treating an etching solution in order to circulate and reuse an etching solution used in etching treatment of silicon includes (1) selectively removing multivalent ions having a valence of two or more, or (2) removing multivalent ions having a valence of two or more, 20-50% of alkali metal ions having a valence of one relative to a total amount of the alkali metal ions, and hydroxide ions, through a membrane separation unit comprising a nanofiltration membrane. A permeated solution of the membrane separation unit is circulated to the etching bath.

Abstract: A nitrogen compound-containing acidic liquid such as a monoethanolamine-containing dilute hydrochloric acid waste liquid discharged during the regeneration of condensate demineralizers in nuclear power plants or thermal power plants is efficiently and economically treated. A neutralization dialysis device 2 is provided in which a raw water chamber 22 and an alkaline solution chamber 23 are partitioned from each other with an anion exchange membrane 21. The nitrogen compound-containing acidic liquid is passed through the raw water chamber 22, while an alkaline solution is passed through the alkaline solution chamber 23, thereby neutralizing and demineralizing the acidic liquid. Thereafter, the nitrogen compound contained in the neutralized demineralized liquid is concentrated with an electrodeionizer 4. The neutralization dialysis treatment using the anion exchange membrane 21 and the alkaline solution can neutralize and demineralize the nitrogen compound-containing acidic liquid.

Abstract: An apparatus and method for treating an etching solution, where the replacement frequency of the etching solution is reduced, while the inclusion of impurities in the treated etching solution is prevented. An apparatus for treating an etching solution in order to reuse the etching solution used in etching treatment of silicon, where the apparatus includes: membrane separation means 3 which performs membrane separation treatment on the etching solution supplied from an etching bath 2; and circulating means 6 which circulates a permeated solution supplied from the membrane separation means 3 to the etching bath 2. The membrane separation means 3 includes a UF membrane module 4 and an NF membrane module 5. Alkaline and organic substances may be added to the etching solution supplied from the membrane separation means 3.