Today it is especially important to develop and evaluate a new, innovative wastewater and sludge management technology. Clearly such a process must be environmentally friendly and cost-effective. As population densities and supporting industrialization increase, there must be a new vision and an effective combination of good science, advanced technology, and prudent leadership.

There has always been a quest for better health. In terms of wastewater treatment there are some notable milestones: (a) in approximately 1829 large-scale sand filtration technology began to improve significantly the life span of the people; (b) in 1875 the use of primary sewage treatment became increasingly attractive as a means of pretreatment of domestic wastes prior to release; and (c) in 1914 the activated sludge process started to contribute to wastewater cleanup. Societal reactions in the 1950's initiated a new strategy for dealing with environmental issues. Throughout this time the emphasis was to build single-media, multi-train, end-of-pipe wastewater treatment systems and open-air incinerators. Many of the historical concepts were never applicable for the demands of the 21st century. The old treatment methodologies have produced unwanted by-products, massive amounts of residual sludges, questionable liquid effluents, leachable ash, excessive suspended solids, noxious gaseous products, and generally incomplete treatment.

The new supercritical water oxidation (SCWO) methodology has the potential to change the whole concept of wastewater treatment, reuse, and environmental acceptability. With the use of supercritical water (SCW) and an oxidant, the complete destruction of complex organic molecules is readily achievable. Residuals such as heat, water, carbon dioxide, nitrogen, inorganic ionic species or salts, and oxidized ash are either recoverable or environmentally acceptable. The SCWO process can serve as a pretreatment unit and end-of-pipe facility, or it can be part of an integrated by-product recovery unit associated with a mainstream chemical process. For almost a decade the University of Texas at Austin SCWO research team of approximately 50 graduate students and 10 full-time researchers has established an in-depth understanding of SCW and SCWO, developed a wide range of treatability data, and validated design models.

While SCW chemistry is complex, the technology associated with SCWO operation is manageable. As water reaches its vapor-liquid critical point (374.2 ^oC and 22.1 Mpa), the physical-chemical properties undergo marked changes. This SCW regime can influence both the design and operation of an SCWO facility. For example, as a result of significant reduction in dielectric constant and density, SCW exhibits characteristics of a non-polar solvent in which organic compounds become miscible. Diffusivity and ion mobility are higher in SCW. The specific heat capacity of water approaches infinity at the critical point. Density varies rapidly with small changes in temperature and pressure. Because of these unique properties, SCW is an excellent medium for reaction, separation, and heat transfer.

The University of Texas SCWO research facility consists of several laboratory-scale batch and continuous-flow reactor systems, as well as a 5 liter/min pilot plant. Additional experimental equipment includes catalyst test assemblies, corrosion rigs, in-situ solid removal devices, and magnetically stirred autoclaves. The highly instrumented pilot plant is capable of performing large-scale treatability, process control, and integrated studies involving various unit operations.

Extensive research and development, as well as full-scale industrial demonstration, have shown that SCWO can be an economical waste management alternative. This hydrothermal process is capable of providing an exceptional, high-quality effluent, producing recoverable energy, separating potential inorganic and organic by-products, and meeting foreseeable environmental requirements.