An apparatus and method for irradiating a fluid containing a material to be irradiated, comprising at least one irradiation chamber having at least one inlet port and outlet port, at least one fluid cooling chamber having at least one inlet port and outlet port, one or more UV radiation sources coupled to the irradiation chamber(s); and at least one heat exchange mechanism thermally coupled to the radiation source(s) and the cooling chamber(s). At least a portion of the interior surface of the cooling chamber(s) may comprise at least a portion of the exterior surface of the irradiation chamber(s) so the cooling chamber(s) is in fluid communication with the irradiation chamber(s).