A scheme has been proposed for treatment of municipal solid waste (MSW) using an press for phase separation (separation of the easily biodegradable fraction from the other constituents) with wet air oxidation. A prototype press was built. One tonne of waste was manually sorted and 6 identical subsamples reconstituted which were used to study the influence of the pressure on the performance of the press and on the quality of byproducts. The first results show that the extraction of the pulp is not complete with a working pressure of 800 bar although the volume reduction of the waste is almost the same as with the other experimented pressures. The glass content of the pulp is about 1%. The proportion of plastics increases when the pressure rises above 800 bar but their granulometry is mostly greater than 4.76 cm. As they are embedded in organic matter they cannot be eliminated at this stage of the process, this would be easier after biological treatment. Concentrations of trace metals are clearly lower than those obtained by traditional mechanical sorting of organic matter. The pulp seems to be well adapted to anaerobic digestion and composting. Analyses of the composition of fines in the pancake and of the concentrations of trace metals, plastics and glass in the pulp do not provide sufficient elements to choose between 1080 and 1300 bar. However, the concentration of products which are not easily biodegradable increases when the pressure is increased from 1080 to 1300 bar. A working pressure of 1080 bar proved to be the optimum: a good rate of organic matter extraction and production of a stable dry matter with a high density. Experiments on individual components of waste (cellulose, plastics, textiles, rubber etc), show that wet air oxidation can be adapted to this kind of solid waste. The results show that the proposed scheme for municipal solid waste treatment is realistic.