Study On The Removal Of VOCs From Water By Membrane Air Stripping

Membrane air stripping (MAS) is an innovative membrane sepration technology developed in recent years for removing volatile organic compounds (VOCs) from wastewater. This study mainly focused on the removal of methyl tert-butyl ether (MTBE), which is one of the most typical VOCs, from simulated wastewater by MAS.The installations for MAS were set up and a series of experiments were carried out. The mainly factors affecting the removal rate such as initial MTBE concentration, temperature, gas velocity, liquid velocity and gas pressure were mostly considered. The results showed that MTBE removal was enhanced by increasing the temperature, gas velocity, liquid velocity and an increase in initial MTBE concentration of the aqueous solution, gas pressure had little effect on the removal efficiency. The MTBE removal efficiency was certainly affected when there is some other organic in the simulated wastewater. The results of the orthogonal experiment indicated that the gas flowrate was the most significant influential factor, and the membrane air stripping was an effective technology to remove MTBE from water as the removal rate can achieve 97%.The process of mass transfer for VOCs was also investigated and analyzed during MAS. A mass transfer model describing the mass transfer during the MAS between the liquid, the gas and the membrane in the hollow fiber membranes was then established based on the double-film theory. The equations to calculate the overall mass transfer coefficient were derived. The mass transfer coefficients in different operating conditions were measured. The calculating results show that the overall liquid-phase mass transfer coefficient did not change when the initial VOCs concentration had changed; hence MAS had potential for industrial wastewater application for removal/recovery of organics in a wide range of concentrations. The overall liquid-phase mass transfer coefficient increased with gas velocity increased, however when the gas velocity became a certain extent, the increment became gradual. There existed a certain optimum air velocity for applacation.The mechanism of mass transfer for VOCs was also investigated. Comparing the experimental data with the theoretic data, Lévésque correlation was found to overestimate the local mass transfer coefficient in a cylindrical tube at low velocities. A modification of this correlation had been proposed to predict the local air film mass transfer coefficient. The proposed correlation predictions matched well with the experimental data. A complete mathematical model was proposed for the removal of VOCs from aqueous solutions by MAS.