Bio-refractory wastewater treatment is compulsory for a safe discharge into the environment. This paper aims to study the use of membrane processes to concentrate wastewater to be then treated by a hydrothermal process such as wet air oxidation for advanced and intensified wastewater treatment. The work focused on three different synthetic wastewaters of public or industrial interest: pharmaceutical wastewater, grey wastewater, and bilge wastewater. Membrane processes operated at the pilot scale enabled retentions as high as 100% of total organic carbon, more than 99% of turbidity, and 70% of hydrocarbon, respectively. High concentration factors were obtained. Membrane foulings were chemically reversible whatever the type of wastewater or the membrane process. Thanks to membrane filtrations, the volumes to be treated by wet air oxidation were drastically reduced, leading to high energy savings. Membrane retentates were then treated by wet air oxidation (300 degrees C, 15 MPa) and resulted in more than an 83% mineralization rate, regardless of the effluent. The hybrid intensified process presented in this work strongly increased the possibility of discharging into the environment by mixing the process outputs or greatly reducing the discharge volume and ultimately the waste load.