| Water pollution in china is aggravating, and thus leads to a serious shortage of water resources; meanwhile our environmental protection technology is still relatively behindhand. Many problems exist in traditional aeration technologies, such as low oxygen utilization ratio, high energy consumption, air pollution and so on. But all these problems can be solved by using hollow fiber membrane bubbleless aeration technology which greatly improves the utilization of oxygen and mass transfer rate, and no bubbles are formed during the process. Bubbleless aeration, with its feature of high efficiency and energy saving, is a promising technology.In this paper, polypropylene hollow fiber microporous membrane was prepared, with average pore size 0.15μm, whose advantages include high porosity, large membrane area per unit volume, high gas flux, as well as low price. Then The membranes were hydrophilic treated by industrial alcohol.A novel curtain type bubbleless membrane aeration device was designed and manufactured by using the PP membranes. The influences of process parameters, like hydraulic factors and gas-phase factors, on oxygen transfer in cross flow and parallel flow conditions respectively were evaluated. It is indicated that oxygen transfer ability grows significantly with the increase of liquid velocity, air pressure and membrane areas. Besides, the membrane resistances and liquid phase boundary layer resistances were calculated, and the results show that the membrane resistances are significantly influenced by gas pressure. As for the discrepancy of cross flow, additional area correction factor fαwas incorporated. Then the membrane resistances correlation was established. In addition, the mass transfer correlations we achieved are in a good agreement with those in paper, especially when Re is low.Besides, a column type bubbleless membrane aeration device was also designed and manufactured. The advantage of this module is that the gas phase pressures can be further increased by enhancing the liquid phase pressures. The DO value at the outlet can reach up to 9.9ml/L, which is far saturated with oxygen, when the liquid phase pressure is at 0.2MPa, the pressure difference is at 0.1MPa and the flow rate is at 600L/h. The oxygen transfer rate in column type is two times larger than that of curtain type.Furthermore, considering the slow rate of oxygen diffusion in water, a rotary type bubbleless membrane aeration device was also designed and manufactured. The influences of process parameters, like hydraulic factors and gas-phase factors, on oxygen transfer in water were evaluated. The results showed that DO value grows with the increase of gas pressures and rotating rate. There is no significant difference by using PP and PE hollow fiber microporous membranes for bubbleless aeration. Later on, the experiment was conducted in synthesized sewage. The module have run for three months, and the results showed that the DO value at the edge of the tank was 0.2-0.3mg/L, while 0.5-0.6mg/L at the center. The COD removal was up to 81.2%.Finally, another novel self-suction bubbleless membrane aeration device was designed and manufactured in this study, which is exposed to the air directly. When the fluid goes through the hollow fiber tube under a certain flow rate, due to its porosity, negative pressure will be formed in the pores and thus the air will be inhaled into tube and mixed with water. It is showed that when the velocity was low, self-suction phenomenon cannot be caused. Therefore, the major influences on oxygen transfer were liquid-gas contact time and contact area. While the velocity was up to critical velocity, normally at 0.4-1.4 m/s, self-suction phenomenon would occur, and there are significant change both in DO value and oxygen transfer rate. In that situation, the liquid phase velocity was the key factor. It indicated that the oxygen transfer rate in self-suction modules is one order of magnitude higher than in previous modules.
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