Performance of tiny microbubbles enhanced with "normal cyclone bubbles" in separation of fine oil-in-water emulsions

This paper presents the results of using tiny microbubbles (MBs, diameter range: 1-16 mu m, D-32 = 6.59 mu m) and MBs combined with normal cyclone bubbles (NBs) for the separation of finely emulsified oil (EO, d < 16 mu m, D-32 = 6.31 mu m) by a modified column flotation. EO samples were prepared from a palm oil product (Z67, Japan) and warm tap water, and the chemical oxygen demand (COD) of the influent and effluent was measured to estimate the treatment performance. The experiments were conducted in batch mode to observe the effects of treatment time, NB flow rate, initial EO concentration, pH, temperature, and salinity (NaCl) on the flotation method. Treatment by a combination of MBs with NBs was more efficient for EO separation than was treatment by MBs alone. For instance, at an EO concentration of 1009 mg L-1 and under identical treatment conditions (treatment time: 60 min, pH: 7.0, temperature: 36.5 +/- 0.5 degrees C, and salinity: 0.0 mg L-1), treatment by MBs and an MB/NB combination (NB flow rate: 2.5 L min(-1)) yielded high EO removal efficiencies of 73% and 86%, respectively. The EO separation efficiency was steady under neutral (pH 7.0) to acidic (pH 3.1) conditions. Temperature and salinity significantly enhanced the efficiency of the flotation process. In the separation of oil-in-water emulsions, a modified column flotation method, which uses a variety of gas bubbles, was shown to be a high-potential approach for reducing the floated product and enhancing oil recovery; this simple method could also be applied for the design of an oil field wastewater treatment plant. (c) 2013 Elsevier Ltd. All rights reserved.