The effect of water composition on the air stripping of volatile organic compounds from groundwater.

Abstract

The objective of this study was to examine the effect of water composition on the air stripping of volatile organic compounds (VOC) using a countercurrent packed column. Henry's Law constants were determined for various VOC of environmental significance: CH$\sb2$=CCl$\sb2$; CH$\sb3$CHCl$\sb2$; CHCl$\sb3$; ClCH$\sb2$CH$\sb2$Cl; CH$\sb3$CCl$\sb3$; CCl$\sb4$; CCl$\sb2$=CHCl; C$\sb6$H$\sb6$; CHBr$\sb3$; and C$\sb6$H$\sb5$CH$\sb3$. The experimental technique consisted of the multiple equilibration of an aqueous solution with the measurement of the liquid-phase VOC concentration. The mass transfer experiments were performed to establish the effect of liquid and gas flow rates, conductivity and packing type on the air stripping of VOC and to evaluate the various mass transfer correlations available. The experiments were conducted using a four-factor, three-level fractional factorial design consisting of 27 runs (Bacon, 1970). The factorial analysis was performed by a SAS general linear regression analysis. The equilibria studies indicated that the Henry's Law constants increase by approximately 30 to 40% with every 10$\sp\circ$C change in temperature and decrease approximately 5 to 15% with every 1000 $\mu$mho/cm change in conductivity. SAS analysis of the equilibria runs showed that temperature was highly significant and conductivity was only slightly significant in the determination of H$\sb{\rm C}$. The mass transfer studies indicated that the Onda et al. correlation gave the best prediction of K$\sb{\rm L}$a for VOC (SEE = $\pm$3.6%) of the correlations studied. The mass transfer studies indicated that KLa decreased by approximately 3 to 5% with every 1000 $\mu$mho/cm change in conductivity. SAS analysis of the mass transfer experiments indicated that the liquid flow rate was a highly significant factors in the determination of K$\sb{\rm L}$a and to a lesser degree conductivity and packing porosity while K$\sb{\rm L}$a is not significantly affected by changes in the gas flow rate. (Abstract shortened by UMI.)