contaminant (an indirect parameter that is correlated to vapor pressure and solubility). The study concluded that substantial codistillation occurred, especially in the first fraction (14%) of the total starting volume of water distilled. Later aliquots of distilled water contained markedly less contaminant. It should be noted that reverse osmosis was not used aboard US Navy ships during the Vietnam War.

The study showed that there may be some codistillation of semi-volatile contaminants during distillation. If the purpose of this experiment was to demonstrate the plausibility of TCDD exposure to sailors via distilled water, then this study is useful; however, the application of these findings to actual shipboard distillation systems requires knowledge of several factors not addressed in the experiment. The significance of this study’s findings for contaminant exposures on Blue Water Navy ships is highly uncertain. Therefore, an independent analysis was conducted in order to determine the likelihood of codistillation of TCDD; this analysis was conducted using a theoretical model.

BATCH DISTILLATION MODELING TO SIMULATE THE AUSTRALIAN STUDY EXPERIMENTAL DATA

The committee considered an equilibrium vaporization process in which the entire feed liquid is charged to the still pot and heat is added continuously. Vapor is continuously produced and removed from the well-mixed vessel. In this batch mode of operation, the liquid product is removed at the end of the run. The operation is often called Rayleigh or batch distillation.

Simulating the NRCET Study

The batch distillation experiment was simulated by solving physical and thermodynamic equations using conditions identical to those of the NRCET study experiments and TCDD as the contaminant. Details of the equations follow. The parameters needed for the calculations based on the conditions of the experiments are as follows:

  • Initial TCDD concentration: 40 ng/L (or initial mole fraction, xD = 1.242 × 10−12).

  • Initial amount of feed, L0: 1 kg (1 L).



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