Charun Bunyakan, Saowapak Malakarn, and Chakrit Tongurai

pp. 255 - 271

Abstract

Volatile organic compounds (VOCs) have been found in wastewater of many chemical industries.
Evaporation of VOCs from open water basin in waste treatment facilities causes air-pollution and has been
regulated in many countries. Reduction or prevention of VOCs evaporation from open water basin is then
necessary. The aim of this research was to investigate the influence of surface film generated by an insoluble
surfactant on the mass transfer coefficient of VOCs evaporating from water. Hexadecanol and octadecanol
were used as surfactant in this investigation with the amount in the range of 0 to 35 µg/cm² and 0 to 25 µg/cm²,
respectively. The VOCs used in this study were methanol, acetone, methyl ethyl ketone and toluene. The
experimental results showed that the surfactant film can reduce the gas film and liquid coefficients by 56
and 80 %, respectively. The suitable amounts of the surfactant were 25 µg/cm² for hexadecanol and 15 µg/cm²
for octadecanol. From this investigation we can conclude that covering the water surface with a film of
hexadecanol or octadecanol could significantly reduce the VOCs evaporation rate. Finally, the empirical equations correlating gas film and liquid film coefficient to amount of surfactants were developed and verified against the experimental data. The predicted values of the overall mass
transfer coefficients, obtained by using these empirical equations, were in good agreement with the measured
values. Thus the empirical equations of mass transfer coefficients developed in this work can be used to
predict the evaporation rates of VOCs from water surface covered by hexadecanol or octadecanol film.