Mass Transfer Coefficients and Henry's Constants for Packed-Tower Air Stripping of Volatile Organics: Measurements and Correlation

摘要

Design of packed-tower air-stripping systems for the removal of volatile contaminants from groundwaters requires knowledge of the equilibrium constant relating air and water concentrations (Henry's constant, H), and the applicable mass transfer coefficient (K sub 1a). The objectives of this research were: to evaluate the effects of temperature, ionic strength, and the mutual presence of other organics on the H-values of five volatile compounds of concern to the USAP; and to investigate the effects of temperature, packing size and type, liquid and air loadings, and the mutual presence of other organics on the K sub 1a values of these five compounds--tetrachloroethylene, trichloroethylene, 1,1,1-trichloroethane, chloroform, and methylene chloride. An innovative method for measuring Henry's constants was proposed and evaluated, termed Equilibrium Partitioning In Closed Systems (EPICS). This method relies upon measurement of the ratio of headspace concentrations from two equilibrated bottles containing equal solute masses, but possessing differing liquid volumes. H-values for the five compounds were measured over temperatures ranging from 10 to 30 C using both EPICS and batch, diffused-bubble stripping techniques. Temperature regressions for H were derived. Comparison between methods suggests that EPICS is as precise as the batch-stripping technique, and is probably more accurate, being free of mass transfer limitations. Liquid-phase diffusivity values were measured for the five study compounds at 20 C using a diaphragm diffusion cell.