Supercritical water oxidation (SCWO) has been shown to be an appropriate technology for the treatment of water containing toxic and hazardous substances, because it provides high destruction efficiencies. This paper reports a study of alternatives, and optimisation of various parameters and conditions, which are applied to the design of a mobile treatment unit. Phenol was selected as a model organic compound present in the feed stream and NaCl was selected as a model polar compound for solid separation. Pilot plant results show that efficiencies above 99.9% in phenol destruction are reached, at an operation temperature of about 650 degreesC, with stoichiometric amounts of air. Feed streams with a wide range of heating values (lower limit 530 and upper limit 930kJkg(-1)) can be handled, because these values allow both thermal and mechanical energy recoveries, which are the key factor for economic feasibility. The unit is capable of handling wastewater containing toxic, recalcitrant or nonbiodegradable compounds that cannot be treated with global streams at the wastewater treatment plant of a factory. It is specifically proposed for use in industries in which wastewater contains solvent mixtures of fine chemicals and pharmaceuticals.