Enhanced treatment of practical textile wastewater by microbubble ozonation

In this paper, microbubble technology was employed to increase the mass transfer rate of ozone and enhance the ozone oxidation of practical textile wastewater. Experiments were performed using a microbubble generator and a bubble contactor, which is commonly used in ozonation system, for comparison. The microbubble generator produced a milky and high intensity microbubble solution, which could reach a higher oxygen transfer rate at a lower input gas flow rate. A volumetric oxygen transfer rate (VOTR) of 0.086-0.413 kg/m(3) h and a total mass transfer coefficient of 0.1072-0.4859 min(-1) were obtained at airflow rates of 0.02-1.5 dm(3)/min. During the ozonation of practical textile wastewater by using the microbubble system, the input ozone could be almost completely utilized, and the rate of decolorization and organic reduction were much faster than those of the bubble contactor. For the practical textile wastewater tested, the time required for 80% removal of color was about 140 and 280min by ozone microbubble and conventional bubbles, respectively. The chemical oxygen demand (COD) removal efficiency in the microbubble system was higher by 20%. The results revealed that in addition to the enhancement of the mass transfer of ozone, microbubbles could improve the oxidation of actual textile wastewater. (C) 2008 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.