A liquid treatment system comprising at least one ultra-violet light treatment lamp arranged within an elongated protective UV-transparent sleeve provided along a central longitudinal axis A, said sleeve having an outer surface and an essentially circular cross-sectional shape; and an elongated reactor configured to receive said sleeve, whereby an elongated liquid treatment chamber for receiving liquid to be treated, is provided between an inner surface of the reactor and the outer surface of the sleeve; wherein said liquid treatment system further comprises at least one elongated cleaning device provided side by side with the sleeve within the liquid treatment chamber and along at least a part of the length of the elongated sleeve, wherein said at least one cleaning device is compressed towards the outer surface of the sleeve by the reactor, and wherein at least one of the sleeve and the reactor is configured to rotate around the longitudinal axis A such that the at least one cleaning device will be touching and cleaning the outer surface of the sleeve over essentially the whole circumference of the sleeve.