In addition to regulatory barriers to technology development, there may be some technological limits to resource recovery. Although a comprehensive study of the issue has yet to be performed, some observations about current practices may be illuminating. Consider Figure 32.2, which provides an overview of hazardous waste management practices in the USA. A striking feature of waste management practices is the relatively limited range of technologies employed. Combustion, land disposal, solvent recovery, metal recovery and a few types of wastewater treatment technologies dominate. Notably absent is the impact of waste exchanges, catalytic reduction and other resource recovery methods. A quantitative analysis of the technological potential for resource recovery may remain elusive, but the Gibbs-Dühem equation of thermodynamics can provide an upper bound on the range of possibility. A simple calculation reveals that the entropy that needs to be overcome in separating a pound of pure material from a million pounds of waste has an energy equivalent of a few hundred to a thousand BTU (the amount of energy in about an ounce of gasoline). Although this calculation is highly idealized, it reveals that fundamental physical laws do not inhibit resource recovery from dilute streams. Rather, the limits are technological.
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