HIGH OXYGEN-TRANSFER RATE IN A NEW AERATION SYSTEM USING HOLLOW FIBER MEMBRANE

A new type of bubble aeration column called a hollow fiber membrane (HFM) aeration column was proposed, which was featured in the use of hollow fiber membranes and gave a high bubble density in the column. The value of k(L)a was increased by modifying the membrane surface for making the pore size smaller. The Sauter mean diameter of bubbles (D(vs)) was 2.0 +/- 0.1 mm in the range of the superficial gas velocity f rom 0.02 m s-1 to 0.065 m s-1, while that obtained for the bubbles near the membrane was 811-mu-m at the superficial gas velocity of 4.0 X 10(-4) m s-1. The difference was ascribed to the effect of coalescence of bubbles. The value of k(L)a increased in proportion to the superficial gas velocity up to 0.02 m s-1, and was almost constant above 0.03 m s-1. The maximum value of k(L)a, 2.5 s-1, was higher than those of the other aeration columns reported previously. The pneumatic power consumption per unit liquid volume (P(v)) for obtaining the same k(L)a was the smallest in the HFM aeration column compared with other types of aeration columns. P(v), for obtaining the same interfacial area of bubbles per liquid volume, was also lower than those for other types of aeration columns. It was suggested from the measurement of bubble diameter that the larger interfacial area generated in the HFM aeration column ascribes to the larger gas holdup than the smaller D(vs).