The invention relates to a system capable of a germicidal treatment of highly opaque liquids, featuring a filter, which prevents wavelengths above the UV-C spectrum reaching the liquid being treated, one or more spiral-shaped tubes extending from an inlet end to an outlet end creating a fluidic pathway, and one or more light sources illuminating the one or more spiral-shaped tubes, wherein the one or more light sources emit light in a wavelength range between 180-300 nm. In particular, the system is a photo bioreactor for pasteurization of liquid food products, the reactor comprising: a. one or more spiral-shaped tubes extending from an inlet end to an outlet end creating a fluidic pathway, and b. one or more light sources illuminating the one or more spiral- shaped tubes, wherein the one or more light sources emit light in a wavelength range between 180-300 nm, wherein the photo bioreactor further comprises one or more filters positioned between the one or more light sources and the one or more spiral-shaped tubes, wherein the one or more filters prevent light above a wavelength of 300 nm from reaching the one or more spiral-shaped tubes. The invention also comprises the use of said reactor for cold pasteurization of liquid food products.
