This work aims to analyse the performances of a new hybrid process: membrane filtration to concentrate biorefractory wastewater before being treated by a hydrothermal process such as wet air oxidation. The aim is to obtain a complete discharge of the effluent in the environment. The three different synthetic wastewaters under study were pharmaceutical wastewater, grey wastewater and bilge wastewater. The results of the membrane filtration showed high retention rates as it could reach between 75% and 100% of total organic carbon rentention, more than 99% of turbidity removal and more than 70% of hydrocarbon retention. Moreover, it was possible to achieve high concentration factors comprised between 17 and 40 times. Membrane fouling was chemically reversible regardless of the type of pollution. Then, the treatment of the membrane retentates by wet air oxidation process (300 °C, 15 MPa) could eliminate more than 83% of organic pollution for all the tested effluents. In summary, the hybrid intensified process could finally decrease the volume and the waste load of wastewater before possibly discharging it into the environment.