A model was developed to simulate the flow properties of suspended packing materials in the biological contact oxidation tank according to the FLUENT multi-phase flow modeling. The distribution of suspended packing materials was improved by optimizing the oxidation tank structure and aeration intensity distribution. The results indicated that the ratio of length to width and aeration intensity distribution played the key role in uniform mixing of the packing materials in the oxidation tank. The tank was divided into four subsections using separation wall

which reduced the ratio of length to width from 7.1 to 1.8. Subsequently

instead of accumulating at the end zone of the oxidation tank

the biological packing materials could be evenly distributed in four subsections. When water body flew through the overflow hole

the flow rate instantaneously increased due to the narrowing cross section area. The water body at high flow rate collided with that at low flow rate at the surrounding area

resulting in the formation of huge vortex flow field. Thus

it mixed consistently the packing materials and enhanced the dispersion effect of the materials. However

the intersection between the separation wall and side wall of the oxidation tank was subjected to the formation of dead zone. It could be resolved by redistributing the aeration intensity of the subsections. The results suggested that uneven aeration could obviously optimize the flow field

which eliminated the accumulation of the packing materials at the side wall and end zone.