Waste treatment, supercritical water

Research on the applications of supercritical water started in the Institute for Technical Chemistry in the early 90 s. At this time interest was focused on the oxidation of hazardous aqueous wastes in supercritical water (SCWO). Many industrial wastewaters containing highly toxic substances, which cannot be destroyed by biological treatment or disposed of, can be completely converted into harmless products [1-5],... 

A. V. Gidner, L. B. Stenmark and K. M. Carlsson, Treatment of Different Wastes by Supercritical Water Oxidation, Proceedings of the International Conference on Incineration and Thermal Treatment Technologies, Philadelphia, PA, May, 2001 (paper is also available for download at www.chematur.se). 

Ryo Tachino, Tomoya Nonoue, Yoshito Oshima, Novel Treatment of Infectious Medical Waste Using Supercritical Water Oxidation Simultaneous Detoxification and Waste Destruction, 20 (2009), Journal of the Japan Society of Material Cycles and Waste Management, p. 111-118. 

Watei has an unusually high (374°C) ctitical tempeiatuie owing to its polarity. At supercritical conditions water can dissolve gases such as O2 and nonpolar organic compounds as well as salts. This phenomenon is of interest for oxidation of toxic wastewater (see Waste treatments, hazardous waste). Many of the other more commonly used supercritical fluids are Hsted in Table 1, which is useful as an initial screening for a potential supercritical solvent. The ultimate choice for a specific appHcation, however, is likely to depend on additional factors such as safety, flammabiUty, phase behavior, solubiUty, and expense. 

Hydrotheimal oxidation (HO) (also called supercritical water oxidation) is a reactive process to separate aqueous wastes into water, CO9, nitrogen, salts, and other byproducts. It is an enclosed and complete water-treatment process m ng it more desirable to the public than incineration (Fig. 22-25) (Tester et al., op. cit. Gloyna and Li,... 

Direct or technology use use of C02 with different technologies and market applications such as use for oil recovery, for dry cleaning, waste carbonation, food, water treatment or extraction with supercritical C02 compounds, including others. 

Waste water treatment. Supercritical CO2 has been put to use in a variety of industrial waste treatment applications. Clean Harbors Environmental Services, Inc., has used SCCO2 in Baltimore since 1989 to treat wastewater from chemical and pharmaceutical manufacturers. In the process the wastewater is pumped into the top of a 32-ft-high, 2-ft-diameter column, while the CO2 is pumped in from the bottom and percolates up. As the CO2 trowels up it dissolves the organics. CO2 contaminated with organics is at the top of the column, and clean water is at the bottom. The contaminants are incinerated off-site after separation from the CO2 which is recycled. 

Hauptmann, E.G. et al., Strategies for treatment mixtures of bleach plant effluents and waste water treatment sludges by supercritical water oxidation, preprints of papers to be presented at the annual meeting, 80(B), B71-B77, 1994. 

Modell, M., Supercritical water oxidation, in Standard Handbook of Hazardous Waste Treatment and Disposal, McGraw-Hill, New York, 1989, pp. 153-168. 

Rofer CK, Buelow SJ, Dyer RB, Wander JD. Conversion of hazardous materials using supercritical water oxidation. U.S. Patent 5,133,877, 1992 Dell orco PC, Foy BR, Robinson JM, Buelow SJ. Hydrothermal treatment of Hanford waste constituents. Hazard Waste Hazard Mater 1993 10 221. 

Aki SNVK, Abraham MA. An economical evaluation of catalytic supercritical water oxidation comparison with alternative waste treatment technologies. Environ Prog 1998 17(4) 246-255. 

Another very important green chemistry solvent is supercritical water (SCW) [14], Water under supercritical conditions is an extremely powerful oxidizing and cleansing agent that has been proven remarkably promising as a soil decontaminant by efficiently degrading persistent organic toxic wastes that are difficult to eliminate from polluted soils, and in the treatment of several types of industrial wastes such as textile and cellulose wastewater [2],... 

Supercritical Water Oxidation (SCWO) has been proved to be a suitable process for treatment of several toxic and hazardous organic wastes due to its high removal efficiency. SCWO requires of hard reaction conditions (22.1 MPa and over 374°C). Special reactors are needed to support these conditions. An original reactor design is presented here wich has been tested in the treatment of alcohols+ammonia solutions in water. Performance results are presented here for ammonia and alcohols. Destruction efficiency greater than 99.9% are reached for both compounds, probing the correct performance of the reactor. 

Rofer C. K., Supercritical water oxidation for treatment of mixed wastes. Proc, Inc, Symp, 1st., (1991) pp. 278-291. 

Like supercritical carbon dioxide, supercritical water is a very interesting substance that has strikingly different properties from those of liquid water. For example, recent experiments have shown that supercritical (superfluid) water can behave simultaneously as both a polar and a nonpolar solvent. While the reasons for this unusual behavior remain unclear, the practical value of this behavior is very clear It makes superfluid water a very useful reaction medium for a wide variety of substances. One extremely important application of this idea involves the environmentally sound destruction of industrial wastes. Most hazardous organic (nonpolar) substances can be dissolved in supercritical water and oxidized by dissolved 02 in a matter of minutes. The products of these reactions are water, carbon dioxide, and possibly simple acids (which result when halogen-containing compounds are reacted). Therefore, the aqueous mixture that results from the reaction often can be disposed of with little further treatment. In contrast to the incinerators used to destroy organic waste products, a supercritical water reactor is a closed system (has no emissions). 

Most research work on the use of supercritical water has been conducted batchwise and involved non-analytical determinative applications. Thus, supercritical water oxidation (SCWO) was proposed as an alternative treatment for hazardous waste disposal [191] and also as a commercial tool for decomposing trichloroethylene, dimethyl sulphoxide and isopropyl alcohol on a pilot plant scale [192]. Current commercially available equipment (the aqua Critox" system) is usable with industrial and municipal sludge, mixed (radioactive and organic, liquid and solid) waste and military waste. This commercially available treatment has a number of advantages, namely (a) because it uses an on-site treatment method, it avoids the need to transport hazardous materials (b) it ensures complete destruction of organic wastes and allows reuse of the effluent as process water with results that meet the regulations for drinking water and (c) no licence for effluent or air emissions is needed. 

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