A process and system for reducing contaminants contained in a contaminated feedstock comprising mixing the contaminated feedstock with water and at least one of metal scavengers or reactants, to form a feedstock-water-reactant mixture, feeding the mixture under pressure into a hydrothermal purification reactor, wherein the mixture is subject to heat, pressure, and turbulent flow conditions to cause rapid reaction of the inorganic contaminants with the metal scavengers or reactants to form inorganic salts that partition into an aqueous phase and maintaining the temperature, pressure, and turbulent flow conditions of the feedstock-water-reactant mixture for a predetermined space time to prevent the organic portion of the feedstock in the mixture from undergoing a conversion reaction and to form a hydrothermal reactor effluent; and separating the effluent into the aqueous phase containing salts of the inorganic contaminants and an organic phase that contains a lower concentration of inorganic contaminants than the contaminated feedstock.