Abstract: A process to produce a flowable fuel or fuel supplement from solid and/or liquid waste, such as municipal waste, industrial wastes or mixtures thereof and the system to carry out the process in which a feed of solid and liquid municipal waste, industrial wastes or mixtures thereof to a treatment zone under conditions of temperature to produce a solid char and vaporize liquids, recombining the char and the liquids, recovered from the wastes feed, to form a feed slurry containing solids, combining the feed slurry with additional combustible waste liquids which are added at a rate and amount to obtain a fuel slurry of specified properties, particularly specified viscosity and BTU content, subjecting the feed slurry and additional wastes to conditions of attrition in at least one attrition zone to produce a product slurry containing solids of fuel size, recovering the fuel slurry which be used as fuel in partial oxidation processes.