SUPERCRITICAL WATER OXIDATION OF PULP-MILL SLUDGES

Supercritical water oxidation (SCWO) is a new process that can oxidize organics very effectively at moderate temperatures (400-650-degrees-C) and high pressure (25.5 MPa). It is an environmentally acceptable alternative for sludge treatment. In bench-scale tests, total organic carbon (TOC) and halide (TOX) reductions of 99-99.9% were obtained; dioxin reductions were 95-99.9%. A conceptual design for commercial systems has been completed, and preliminary economics have been estimated. Cost comparisons confirm that SCWO is less costly than dewatering plus incineration for treating pulp mill sludges. In addition, SCWO can also compete effectively with dewatering plus landfilling where tipping fees exceed US$ 45/m3.