NOVELTY - The method comprises adding oxidant such as oxygen and/or hydrogen peroxide to the digester material, where the oxidant provides dissolved oxygen, and pressurizing the digester material to elevate or sustain the dissolved oxygen concentration relative to the dissolved oxygen concentration achieved upon addition of the oxidant. The digester material comprises 5-5000 milligrams of iron per liter of digester material. The pH and temperature of the digester material following pressurization are natural pH and temperature. The iron is added to the digester material at the collection system.    USE - The method is useful for enhancing an anaerobic digestion of digester material such as digester influent, digester effluent, settled solids from a digester and/or supernatant from a digester (claimed) in municipal wastewater treatment, agricultural operations and biofuels production.    ADVANTAGE - The method efficiently and controllably enhances the anaerobic digestion of digester material by adding iron to anaerobic digesters thus enabling easy and economical anaerobic treatment of large amount waste water in an eco-friendly manner, reducing the volume of residual solids, pathogens and odors and improving the efficiency of the biofuels production.    DETAILED DESCRIPTION - The method comprises adding oxidant such as oxygen and/or hydrogen peroxide to the digester material, where the oxidant provides dissolved oxygen, and pressurizing the digester material to elevate or sustain the dissolved oxygen concentration relative to the dissolved oxygen concentration achieved upon addition of the oxidant. The digester material comprises 5-5000 milligrams of iron per liter of digester material. The pH and temperature of the digester material following pressurization are natural pH and temperature. The iron is added to the digester material at the collection system, the treatment plant headworks, the primary clarifier influent, the primary thickener influent, the digester influent or a recycle line to/from the digester. The dose of the oxidant is 10-10000 milligrams of oxidant per liter digester material. The pressurizing step comprises subjecting the digester material to pumping, mixing, ultrasound, hydrodynamic cavitations and/or endogenous decomposition of hydrogen peroxide, applying a moderate pressure of 50-350 psig to the digester material, and applying a low pressure of 5-25 psig to the digester material. The pressurization of the digester material accelerates oxidation of sulfide and ferrous iron in the digester material to elemental sulfur and ferric iron. The digester material and oxidant are pressurized within a pressure oxidizer device (100). The dissolved oxygen concentration of the digester material is less than 10 mg/L. The oxidant is added to solids of the digester material prior to entry of the digester material into the anaerobic digester. The oxidant is added to the supernatant of the anaerobic digester effluent subsequent to dewatering but prior to the anaerobic digester to oxidize sulfide and ferrous iron to elemental sulfur and ferric iron. INDEPENDENT CLAIMS are included for:    (1) a pressure oxidizer device; and    (2) a wastewater treatment system.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of a pressure oxidizer device of wastewater treatment system.    Pressure oxidizer device (100)    Pressure pipe reactor (110)    Pressure indicator (111)    Pressure safety valve (112)    Flow restriction/backpressure regulator. (113)