BACKGROUND: Comparison experiments were carried out with three kinds of micro-bubbles on the coagulation flotation process treatment of coke waste-water under optimum coagulation conditions obtained from zeta potential measurement. RESULTS: Micro-bubble flotation with ozone showed the best performance. The ozone micro-bubbles exhibited high absolute zeta potential values, creating repulsion forces thus avoiding the coalescence of bubbles as well as creating attractive interaction between bubbles and particles in the waste-water. Moreover, the fluorescence intensity of three micro-bubble samples showed that the ozone micro-bubble system produced the most hydroxyl radicals, which contributed to the degradation of organic material in the coke waste-water. Compared with either air micro-bubble flotation and oxygen micro-bubble flotation processes, pyridine removal efficiency of the ozone micro-bubble flotation process was, respectively, 4.5 and 1.7 times higher, and benzene removal efficiency 3.6 and 1.5 times higher. Finally, drainage models and oxygen diffusion models of the three kinds of micro-bubble water samples verified the long persistence of the three kinds of micro-bubbles in the water. CONCLUSION: The application of ozone micro-bubble technology in coagulation processes may provide an efficient and cost-effective approach to the treatment of waste-water containing refractory organic compounds. (C) 2011 Society of Chemical Industry