Provided is a production method for a concentrated product, using a freeze-concentration method having a high yield rate (low loss rate) that is practically applicable, as required in large-scale (commercial scale) production. The production method for concentrated product using the freeze-concentration method includes: an ice crystal generation step in which a fluid to be treated is cooled, ice crystals of the fluid are generated in the fluid, and a mixed fluid to be treated is formed wherein the mixed fluid to be treated is comprised of the ice crystals and a concentrated fluid produced from the fluid to be treated by generating the ice crystals in the fluid thereby the fluid is concentrated; and an ice crystal separation step in which the mixed fluid is separated into the concentrated fluid to be treated and the ice crystals, and the separated concentrated fluid be treated is retrieved.

A method using a membrane-concentration method and a freeze-concentration method includes: a membrane-concentration step in which a fluid to be treated is cooled and a membrane-concentrated fluid is prepared by membrane-concentrating the solid content concentration thereof by more than 1.5 times; an ice crystal generation step in which said membrane-concentrated fluid is cooled, ice crystals of said membrane-concentrated fluid are generated in said membrane-concentrated fluid, and a mixed fluid to be treated is formed wherein said mixed fluid to be treated is comprised of said ice crystals and a concentrated fluid to be treated produced from said membrane-concentrated fluid by generating said ice crystals in said membrane-concentrated fluid thereby said membrane-concentrated fluid is concentrated; and an ice crystal separation step in which said mixed fluid is separated into said concentrated fluid to be treated and said ice crystals, and said separated concentrated fluid to be treated is retrieved.

A method using a membrane-concentration method and a freeze-concentration method includes: a membrane-concentration step in which a fluid to be treated is cooled and a membrane-concentrated fluid is prepared by membrane-concentrating the solid content concentration thereof by more than 1.5 times; an ice crystal generation step in which said membrane-concentrated fluid is cooled, ice crystals of said membrane-concentrated fluid are generated in said membrane-concentrated fluid, and a mixed fluid to be treated is formed wherein said mixed fluid to be treated is comprised of said ice crystals and a concentrated fluid to be treated produced from said membrane-concentrated fluid by generating said ice crystals in said membrane-concentrated fluid thereby said membrane-concentrated fluid is concentrated; and an ice crystal separation step in which said mixed fluid is separated into said concentrated fluid to be treated and said ice crystals, and said separated concentrated fluid to be treated is retrieved.

A method for highly concentrating aqueous solutions containing thermally sensitive organic constituents and with or without mineral constituents, wherein firstly, a major portion of the water is extracted by membrane filtration from the solution for pre-concentration and is discharged from the process and the solution which is pre-concentrated is then subjected to a freeze concentration procedure, in which, in the form of separated ice crystallisate, further water is extracted from the solution. To promote results, that concentration may be effected in the freeze concentration procedure until a viscosity of the mother solution of at least 0.0002 m.sup.2/s is achieved, and in that the separated ice crystallisate from the freeze concentration with the mother solution adhering thereto as a suspension is returned to the membrane filtration upstream of the membrane filtration or after melting of the ice crystallisate.

A method for highly concentrating aqueous solutions containing thermally sensitive organic constituents and with or without mineral constituents, wherein firstly, a major portion of the water is extracted by membrane filtration from the solution for pre-concentration and is discharged from the process and the solution which is pre-concentrated is then subjected to a freeze concentration procedure, in which, in the form of separated ice crystallisate, further water is extracted from the solution. To promote results, that concentration may be effected in the freeze concentration procedure until a viscosity of the mother solution of at least 0.0002 m.sup.2/s is achieved, and in that the separated ice crystallisate from the freeze concentration with the mother solution adhering thereto as a suspension is returned to the membrane filtration upstream of the membrane filtration or after melting of the ice crystallisate.