Liquid treatment system comprising a treatment chamber and a liquid inlet and a liquid outlet connected to said treatment chamber, a guiding unit, at least two racks, comprising a series of n ultraviolet lamp units, where n is equal to or more than 2, disposed in said treatment chamber, which series of ultraviolet lamps are each individually arranged in parallel planes and are connected to one and another in said plane, wherein each rack is individually movable over the guiding unit perpendicular to each plane thereby increasing or decreasing a distance d s between two series, wherein a distance d uv between two adjacent ultraviolet lamp units in a series is substantially constant, wherein a first ultraviolet lamp unit in a first series is located at a distance d uv from a side of the treatment chamber and wherein an n th ultraviolet lamp unit in the first series is located at a distance 1/2*d uv from an opposite side of the treatment chamber, wherein a first ultraviolet lamp unit in a series adjacent to the first series is located at a distance 1/2*d uv from a side of the treatment chamber and wherein an n th ultraviolet lamp unit in the adjacent series is located at a distance d uv from an opposite side of the treatment chamber, and wherein at least one ultraviolet lamp unit is for generating UV-light of a first wavelength for killing microorganisms and for generating UV-light of a second wavelength for providing ozone, wherein series of ultraviolet lamps are each individually arranged in parallel planes substantially perpendicular to a wall of said treatment chamber, wherein the series of ultraviolet lamps are placed in a rack, wherein each series comprises at least one ultraviolet lamp unit for generating UV-light of a first wavelength for killing microorganisms and for generating UV-light of a second wavelength for providing ozone, wherein a UV lamp unit comprises a transparent tube closed at a bottom side thereof, a UV-lamp for generating the first and second wavelength located in the tube, wherein for at least one UV lamp unit an intensity of the first wavelength for killing microorganisms is adaptable between 0-100% of a maximum power capacity, and / or an intensity of the second wavelength for providing ozone is adaptable between 0-100% of a maximum power capacity, an inner tube located in the tube close to the UV-lamp for providing flow of a fluid, an injector in fluid connection with the inner tube, the injector comprising a fluid exit for directing ozone rich gas to the to be treated liquid, wherein UV-lamp units are provided in a substantially vertical mode. a treatment chamber and a liquid inlet and a liquid outlet connected to said treatment chamber, a guiding unit, at least two racks, comprising a series of n ultraviolet lamp units, where n is equal to or more than 2, disposed in said treatment chamber, which series of ultraviolet lamps are each individually arranged in parallel planes and are connected to one and another in said plane, wherein each rack is individually movable over the guiding unit perpendicular to each plane thereby increasing or decreasing a distance d s between two series, wherein a distance d uv between two adjacent ultraviolet lamp units in a series is substantially constant, wherein a first ultraviolet lamp unit in a first series is located at a distance d uv from a side of the treatment chamber and wherein an n th ultraviolet lamp unit in the first series is located at a distance 1/2*d uv from an opposite side of the treatment chamber, wherein a first ultraviolet lamp unit in a series adjacent to the first series is located at a distance 1/2*d uv from a side of the treatment chamber and wherein an n th ultraviolet lamp unit in the adjacent series is located at a distance d uv from an opposite side of the treatment chamber, and wherein at least one ultraviolet lamp unit is for generating UV-light of a first wavelength for killing microorganisms and for generating UV-light of a second wavelength for providing ozone, wherein series of ultraviolet lamps are each individually arranged in parallel planes substantially perpendicular to a wall of said treatment chamber, wherein the series of ultraviolet lamps are placed in a rack, wherein each series comprises at least one ultraviolet lamp unit for generating UV-light of a first wavelength for killing microorganisms and for generating UV-light of a second wavelength for providing ozone, wherein a UV lamp unit comprises a transparent tube closed at a bottom side thereof, a UV-lamp for generating the first and second wavelength located in the tube, wherein for at least one UV lamp unit an intensity of the first wavelength for killing microorganisms is adaptable between 0-100% of a maximum power capacity, and / or an intensity of the second wavelength for providing ozone is adaptable between 0-100% of a maximum power capacity, an inner tube located in the tube close to the UV-lamp for providing flow of a fluid, an injector in fluid connection with the inner tube, the injector comprising a fluid exit for directing ozone rich gas to the to be treated liquid, wherein UV-lamp units are provided in a substantially vertical mode.