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Enhanced ozonation of textile wastewater by microbubbles

In this paper the microbubble technology was employed to increase the mass transfer rate of ozone as well as to enhance the ozone oxidation. Experiments were performed using the microbubbles generator and the bubble contactor, which is commonly used in ozonation system, for the purpose of comparison. The microbubble generator produced a milky and high intensity microbubble solution in which the bubbles had a mean diameter of less than 58 microns, a numerical density of more than 2.9×10 counts/mL, and a specific surface area of more than 334 m at the gas flow rate of less than 0.5 L/min. Compared to the bubble contactor, the total mass transfer efficiency in the microbubble system were 1.6-2.7 times higher. During the ozonation of practical textile wastewater, the input ozone could be thoroughly utilized and the rate of decolourization and organic reduction were much faster by using the microbubble system. The time required for 80% removal of color was about 140 and 280 min by introducing ozone into the microbubble generator and bubble contactor, respectively. The COD removal efficiency was higher 20% by using the microbubble system. The results suggested that in addition to the enhancement of mass transfer, microbubbles, which had higher inner pressure, could accelerate the formation of hydroxyl radicals from the decomposition of ozone and hence improve the oxidation of dye molecules.