The invention relates to a vacuum sewage system, which includes a sanitary unit, such as a toilet unit, vacuum sewer piping (200) connected to the sanitary unit, a discharge valve between the sanitary unit and the vacuum sewer piping, and a vacuum generating device for generating vacuum in the vacuum sewer piping. The system comprises an on-line separator device (1) in the vacuum sewer piping (200, 201) and a first pump means (2) and a second pump means (3) connected in parallel with the on-line separator device (1). The first pump means (2) is a vacuum pump for generating vacuum in the vacuum sewer piping (200, 201) and for evacuating air from the sewage flow flowing into the on-line separator device (1) and the second pump means (3) is arranged for pumping mainly sewage from the sewage flow flowing into the on-line separator device (1).