A UV (ultraviolet) light disinfectant apparatus useful with a biofilm flow cell for in-line, non-invasive disinfecting of medium flow to and from the flow cell is provided. The disinfectant apparatus includes a UV chamber having a UV light source therein and one or more UV light-transmissive tubes that extend through the UV chamber and through which the fluid medium flows through the UV chamber for exposure to UV light for purposes of disinfectation.
