Recirculating air purification system designed for highly germ-contaminated air in food production as well as in smaller cooling and ripening rooms. An axial fan draws in the germ-contaminated room air and guides it inside the recirculating air sterilization unit via high-power lamps. These low-pressure mercury lamps emit UV-C light of exactly 253.7 nm – a spectral line which has a reliable germicidal effect but does not produce ozone.