Experimental Study Of Oily Wastewater Treatment With Multiphase Pump Dissolved Air Flotation

In the thesis, a systematic summary of the development of flotation technology and the research status quo is presented. In view of the advantages of pressurized dissolved air flotation such as simple structure, easy operation, small bubbles and even distribution of the bubbles, a set of pressurized dissolved air flotation apparatus is constructed with a multiphase pump as its air-dissolving device. And the main factors which influence the effect of air flotation are studied in-depth.The air-dissolving performance of the flotation apparatus plays an important role in the process of air flotation treatment. Therefore, the performance of multiphase pump is studied in-depth. By measuring the volume of released air and air-dissolving efficiency under different operating conditions such as different pressure, flow rate and air intake, the performance of the multiphase pump is evaluated. Meanwhile, the variations of mean diameters of released bubbles along with the changes of pressure, flow rate and air intake are also studied. The results indicate that the volume of released air almost does not vary when pressure changes. The maximum volume is greater than 70mL/L, and the mean diameter of the released bubbles is approximately 50 m.In the experiments of oily wastewater treatment with air flotation apparatus, factors such as process load, recycle ratio, types of coagulants, oil content and salinity are studied. The results show that when the oil content of influent is about 200mg/L, oil content can be reduced to about 25mg/L, and the oil removal efficiency exceeds 85%. When the oil content of influent is less than 1000mg/L, the oil content of the effluent remains stable at about 35mg/L. Salinity has a certain impact on the effect of air flotation. The removal is relatively high when the salinity of influent is about 1.5～2.0g/L.In the end of the thesis, the performance of multiphase pump flotation is compared with that of compressed air flotation. The results indicate that both types of air flotation system have high removal efficiency, but the former type has its own advantages such as higher treatment capacity, lower recycle ratio and coagulant dosage, less equipment investment, lower occupied land and no noise pollution. Due to these benefits, it can be predicted that the multiphase pump flotation will be widely used in the treatment of oily wastewater.