| De-inking sludge and its contaminants were studied in supercritical water (SCW), where temperature and pressure are above water's critical point of 374°C & 22.1 MPa. Phase behavior of pure organics in the sludge were studied with a diamond anvil cell (DAC) technique, and optical & FT-IR microscopes. Oxidation experiments in SCW were performed in batch and flow reactors for the complex sludge and pure decachlorobiphenyl (10-CB).; From the visual observations in the DAC, homogeneous phases with water were found for cellulose at 329°C; for naphthalene (NT) at 383°C; for benzo(a)pyrene (BaP) at 508°C and for polystyrene (PS) at 570°C. Adding O2 shifted the formation of the single phase to lower temperature. Complete dissolution of 10-CB occurred only when excess O2 was present (at 548°C with 225% excess O2 or at 450°C for 596 s with 93% excess O2). Adding Na2CO3 significantly enhanced dissolution rate of 10-CB, for example, using 2.5-mol% Na2CO 3, complete dissolution was achieved at 434°C even with low O 2 concentration (69.5% theoretical O2).; The homogeneous conditions are important for the oxidation study of the sludge in batch reactors. Oxidation experiments of heavy metal (Pb, Cr, Cd)-, NT and BaP-contaminated sludge in SCW were conducted. It was found that all organics in the sludge, including stable polycyclic aromatic hydrocarbons could be almost completely oxidized to CO2 and H2O. The water-soluble heavy metal salts were effectively removed by precipitation to insoluble oxides and salts with little leachability. During the oxidation of 10-CB at 225% excess O2, only 99.2% destruction rate was obtained accompanied by severe corrosion of the reactor. However, using 100% theoretical Na2CO3, all 10-CB was destroyed at 159.5% excess O 2 with little corrosion. 10-CB was also successfully destroyed in a flow reactor.; Oxidation pathways of the major components of the sludge and a sequence of corrosion reactions were proposed.; It can be concluded that the SCW oxidation process is an effective technique for the destruction of organic wastes including very stable hazardous compounds (e.g., BaP & 10-CB) due to the homogeneous conditions of chemical reactions and removal of heavy metals. |
