| Abstract: | Wet air oxidation (the patented Zimmermann process) destroys organic matter in sewage sludge by bringing a sludge-air mixture to elevated temperature (260 to 370 °C) and pressure (12.4 MPa) and holding it for a reaction time of 35 to 55 min. These conditions result in 70 to 80% COD removal with carbon dioxide, water, short chain aliphatic acids, and ash as products. Energy recovery provisions enable the process to be self-contained at sludge concentrations of 4.5 to 5% which are difficult to obtain. An additive to the process which would enable successful oxidation to proceed with less concentrated sludge, at lower pressures and shorter times would be useful. Hydrogen peroxide in combination with several metal salts was tested as an additive. Hydrogen peroxide plus dichromate was found to destroy 70% of the COD of a glucose solution (500 mg/1 COD) at 150 °C and 5.2 MPa in 15 min. The ratio of the equivalents of the substances glucose: hydrogen peroxide: dichromate stood as 13 : 6.5 : 1. The amount of COD destroyed exceeded the oxidative equivalents of peroxide and dichromate present; hence it was concluded that molecular oxygen was incorporated in the reaction. |
