A new type of device, a dissolved-air flotation column, was developed for separation of oily wastewater.The unique design idea of the dissolved-air flotation column is the combined use of dissolved-air flotation and column flotation.The dissolved air release occurred within the column separation system.As a potential application the column was investigated for its performance in separating emulsified oil droplets in oily wastewater.A high separation efficiency was obtained in a series of tests.The aeration performance of the bubble generator used in the dissolved-air flotation column was also studied in particular.