Abstract: Heated and pressurized reactant material is caused to come into contact with oxidant in an initial contact zone (Z) within a contactor. vessel (11). This initial contact zone is removed from the walls of the vessel and the structure through which the reactant material is introduced into the vessel. Once in the contactor vessel (11), the temperature of the reactant material is elevated to critical temperature or near critical temperature in at least portions of the initial contact zone. Sulfates and similar ions liberated in the oxidation reaction form salts and precipitate from solution generally in. the initial contact. zone removed from the contactor vessel walls and then tend not to adhere to equipment at points downstream from the initial contact zone.

Abstract: A hydrothermal process (10) is integrated into a wastewater treatment facility (12) to fully oxidize an undigested wastewater sludge produced by the treatment facility. A thickened and conditioned feed mixture comprising sludge from the treatment facility is first pressurized to a critical pressure and then heated to a reaction initiating temperature below the critical temperature. An oxidant is injected into the feed mixture at the reaction initiating temperature to initiate an oxidation reaction in low light-off temperature constituents of the feed mixture to produce a partially reacted mixture and raise the temperature of the partially reacted mixture to at least the critical temperature for water in a supercritical water oxidation reactor (52). Heat from the supercritical water oxidation reaction is used to heat the feed mixture and also, to condition the sludge from the wastewater treatment plant preferably by thickening and heating the sludge.