Synergistic effect of microbubbles and activated carbon on the ozonation treatment of synthetic dyeing wastewater

The performance of catalytic microbubble (MB) ozonation using a commercial granular activated carbon (AC) as catalyst in synthetic acid red 3R wastewater treatment was more efficient than that of coarse bubble (CB) and MB ozonation alone. The ozone mass transfer coefficient, ozone decomposition coefficient, decolorization rate constant, TOC removal rate constant, and ozone reaction efficiency achieved in catalytic MB ozonation were 0.253 min(-1), 0.093 min(-1), 0.342 min(-1), 0.0242 min(-1) and 0.128 mg((TOC removed))/mg((ozone consumed)), respectively. The average ozone utilization efficiency in catalytic MB ozonation was as high as 98.3%. The synergistic effect of collapsing ozone MBs and catalytic activity of AC enhanced hydroxyl radicals ((OH)-O-center dot) oxidation in catalytic MB ozonation which provided about 75% of oxidative capacity for TOC removal, even at a low pH. The enhanced (OH)-O-center dot oxidation was crucial for the mineralization of acid red 3R in catalytic MB ozonation where some (OH)-O-center dot scavengers could make TOC removal less efficient, especially Na2CO3. In addition, the catalytic activity of this commercial AC seemed stable after five recycling cycles. UV-Vis spectra and GC-MS analyses indicated that acid red 3R was oxidized-degraded by a pathway of azo bond cleavage, formation of naphthalene- and benzene-type compounds, further generation and final mineralization of small organic acids, which initially reduced the pH and increased the value again during catalytic MB ozonation. Therefore, the catalytic MB ozonation with commercial granular AC was a promising solution for wastewater treatment by ozonation process.