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LOW-TEMPERATURE, LIQUID-PHASE PROCESSES 126 million or less. Electrical energy has been used to generate the ozone and UV light. TABLE 6-1 Oxidation Potential of Different Chemical Species Oxidation Species Potentiala Fluorine 3.06 Hydroxyl radical 2.80 Atomic oxygen 2.42 Ozone 2.07 Peroxydisulfate 2.06 Chlorine dioxide 1.96 Ag2+ 1.98 Peroxymonosulfate 1.98 Hydrogen peroxide 1.77 Perhydroxyl radicals 1.70 Hypochlorous acid 1.49 Chlorine 1.36 Ferric ion 0.77 a At 1M hydrogen ion concentration. The potentials change with pH. The committee found no information on the treatment of concentrated organic wastes or chemical warfare agents. The best application of this technology would appear to be for final treatment of dilute solutions after bulk destruction and oxidation have been accomplished by other means. BIOLOGICAL PROCESSES Introduction and Overview The use of biological processes to destroy chemical warfare agents is at an early stage of development (Ward, 1991; Harvey and DeFrank, 1992; Landis and DeFrank, 1991). Biological processing may be useful in detoxifying neat organophosphorus nerve agents and in destroying the reaction products from initial chemical detoxification of agents. In general, biological systems
LOW-TEMPERATURE, LIQUID-PHASE PROCESSES 127 are most appropriate for processing dilute aqueous solutions.2 One of the most important issues about the applicability of available systems to chemical demilitarization is whether biological processes or biochemical reactions can be developed into functional engineering processes. The most promising potential applications of biological processes to chemical demilitarization appear to be the following: ⢠direct detoxification of stockpiled organophosphate nerve agents using cellular or enzyme-based reactions (potentially applicable to GB and VX but not to sulfur mustard agents); ⢠biodegradation and mineralization of reaction products from chemical destruction of the nerve agents GB and VX; ⢠biodegradation of thiodiglycol or other products from hydrolysis or chemical oxidation of mustard (H); and ⢠biodegradation used as a final polishing process for aqueous effluents from other detoxifying processes, such as chemical or thermal oxidation. The first two applications use biological processes in the primary detoxification stream or in secondary processing streams. They would entail the modification and integration of large-scale fermentation and waste treatment technologies developed for other applications, but not for agent demilitarization (Irvine and Ketchurn, 1989). If biological processes are used for initial detoxification of agents, the control and management of agent toxicity during fermentations or enzyme-catalyzed reactions would be of critical concern. For example, residual toxicity from the partitioning or sorption of agents onto microbial cell mass or immobilized enzyme support matrices must be considered. In addition, the capability of enzyme or cellular-based processes to completely degrade the agents (e.g., to greater than 99.99 percent destruction efficiency) has not been demonstrated in a practical reactor system. A final consideration is the characterization of gaseous, soluble, and solid by-products of the biological processes. These include waste cell mass (sludge), products of incomplete biological mineralization, and agent or reaction products potentially volafdized during process aeration. 2 Dilution to 5 to 10 percent aqueous solutions is an initial estimate of the maximum concentration of dissolved organic substrates (reaction products from initial detoxification of chemical agents) in solution that would be biodegradable. This is based on previous work in biological treatment of high strength industrial waste waters (Enzminger et al., 1987; Lepore et al., 1989; 1990a,b; 1991). Initial biological treatment studies would need to define this upper concentration limit for the particular reaction products to be treated. This would be accomplished through toxicity inhibition by using a climated cultures.
