An inverse fluidized-bed biofilm reactor (IFBBR) was used for the treatment of highly-emulsified oily wastewater. When the concentration of biomass which was cultivated in the synthetic wastewater reached to 6000㎎/L, the oily wastewater was employed to the reactor with a input COD concentration range of 50㎎/L to 1900㎎/L. Virtually the IFBBR showed a high stability during the long operation period although some fluctuation was observed. The COD removal efficiency was maintained over 90% under the condition that organic loading rate should be controlled under the value of 1.5 ㎏COD/㎥/day, and F/M ratio is 1.0㎏COD/㎏VSS/day at 22℃ and HRT of 12 hrs. As increasing organic loading rates, the biomass concentration was decreased steadily with decreasing of biofilm dry density rather than biofilm thickness. Based on the experimental results, It was suggested that the decrease in biofilm dry density was caused by a loss of biomass inside the biofilm.

Hydrodynamic characteristics such as gas holdup, liquid circulation velocity and bed expansion in a hexagonal inverse fluidized bed were investigated using air-water system by changing the ratio (Ad/Ar) of cross-sectional area between the riser and the downcomer, the liquid level(Hl/H), and the superficial gas velocity(Ug). The gas holdup and the liquid circulation velocity were steadily increased with the superficial gas velocity increasing, but at high superficial gas velocity, some of gas bubbles were carried over to a downcomer and circulated through the column. When the superficial gas velocity was high, the Ad/Ar ratio in the range of 1 to 2.4 did not affect the liquid circulation velocity, but the maximum bed expansion was obtained at Ad/Ar ratio of 1.25. liquid circulation velocity was expressed as a model equation below with variables of the cross-sectional area ratio(Ad/Ar) between riser to downcomer, the liquid level(H1/H), the superficial gas velocity(Ug), the sparger height[(H-Hs)/H], and the draft plate level(Hb/H). Uld=11.62g^0.75(Hl/H)^10.30(Ad/Ar)^-0.52(H-Hs/H)^0.91(Hb/H)^0.13