A dewatering system (1) and method for separating oil/water sludge, such as oil/water sludge generated on a maritime vessel, into a clean water component and a dewatered waste oil component in a repetitive batch process is disclosed. The system (1) comprises a vacuum distillation device (2), the vacuum distillation device having a feed port (8) for loading a batch of an oil/water mixture to be treated, a processing chamber (10) provided with heating means (12, 13) in a bottom portion thereof, means for controlling the heating means, a vapour phase port (14) communicating with a top portion of the processing chamber (10), a vacuum pump (15) connected to the vapour phase port (14) and configured for removing water vapour from the processing chamber (10) so as to reduce the vapour phase pressure therein to below atmospheric pressure, and a waste port (17) configured for retrieving dewatered waste oil from a bottom portion of the processing chamber. The system (1) further comprises a control unit (4) configured to perform one or more control functions for controlling the operation of the system (1) in a programmed manner. A gravitational settling device (3, 203) is provided for pre-treating the sludge to remove continuous phase water prior to loading the distillation device (2).