Abstract: A process and an arrangement for continuously carrying out photoreactions cloudy, colored or UV-absorbing media. The object of providing a possibility for increasing the photon yield while continuously carrying out photoreactions in liquid substances is met in that the liquid dripping down a vertical inner wall of a pipe is wiped vertically to the dripping direction by means of distributor rollers which rotate on the rods of a cage-shaped rotor and is exposed proceeding from the center of the pipe by a rod-shaped photolamp. In this way, a liquid film of defined thickness is produced on the pipe wall and this liquid film is acted upon by immobilized catalyst layers at the pipe wall or at the distributor rollers or by gases introduced into the interior of the pipe to assist the reaction.The process and arrangement are used for photochemical cleaning of media containing chlorocarbons, chlorofluorocarbons and fluorocarbons and for preparing drinking water and highly purified water.