Determining the equilibrium partitioning coefficients of volatile organic compounds at an air–water interface

The single equilibration technique (SET) was adopted to determine the partitioning coefficients (pc) at an air–water interface for volatile organic compounds (VOCs), including ethanol, iso-propanol (IPA), iso-butanol (IBA), methyl ethyl ketone (MEK) and toluene, all extensively used in industrial processes. Standard SET procedures were established. The liquid concentrations (CL) of tested VOCs ranged from 10 to 125 mg l−1 for alcohols and MEK, and from 0.5 to 20 mg l−1 for toluene. The temperatures (Tw) of aqueous VOC solutions were maintained at 27, 32, 38 and 42 °C to determine the gaseous concentrations at equilibrium (Cg*) and pc of VOCs, using the formula pc=(Cg*/CL). Results reveal that the pc values of all tested components increase slowly with Tw given a constant CL, and that the pc of alcohols and MEK fall as CL increases at a constant Tw. In contrast, the pc of toluene is not significantly impacted by a variation in CL at a constant Tw. However, the effect of CL concentration has seldom been discussed. The heats of liquid and gaseous phase transfer (ΔHtr) of VOC, and the highly linear regression (with squared correlation coefficients, R2, from 0.901 to 0.999) between lnCg* and Tw−1 are also evaluated. The experimental results and the VOC mass transfer characteristics are helpful for evaluating the emission of VOC from the water surface of wastewater treatment facilities.