Songklanakarin Journal of Science and Technology (SJST) (Sep 2006)
Mass transfer coefficient for volatilization of volatile organic compounds from wastewater
Abstract
Volatilization of volatile organics compounds (VOCs) from wastewater is recognized as an important source that caused air pollution today. In air pollution management regarding VOCs emission to atmosphere, the amount of VOCs that released from wastewater needs to be known. A model for predicting of VOCs volatilized from wastewater is then necessary. The aim of this research was to develop the gas-film (kGa,VOC) and liquid-film (kLa,VOC) mass transfer coefficients from volatilization of VOCs from wastewater. The volatilization experiments were performed in a pilot volatilization tank with a volume of 100 L. The wind speed over the water surface, measured at 10 cm above water surface (U10cm), was the main parameter which investigated in this work. The U10cm were varied from 0 to 4.42 m/s. VOCs used in this investigation were methanol, toluene and methyl ethyl ketone.The results revealed that the gas-film coefficient of methanol increased linearly with increasing U10cm over the investigated range of U10cm whereas the liquid-film coefficient of toluene fell into two regimes with a break at the U10cm of 2.4 m/s. The correlations of kGa,VOC and kLa,VOC were developed from gas-film and liquid-film coefficient of methanol and toluene, respectively, and verified by predicting overall mass transfer coefficient (KOLa) of MEK. It was found that the correlations of kGa,VOC and kLa,VOC predicted the mass transfer coefficient of MEK which volatilized from wastewater quite well but underestimated KOLa of MEK volatilized from pure water. Since the mass transfer coefficient of VOCs volatilized from pure water were significant higher than that of wastewater as found in this work, the kGa,VOC and kLa,VOC developed based on wastewater is recommended for prediction of VOCs emission rate from wastewater rather than the correlation previously developed based on pure water.
