Gas injection into aeration tanks

Aeration is one of the most common stages in the liquid waste clarification process. Most aeration
tanks are equipped with aeration devices that inject oxygen to enhance the biodegradation of the liquid
waste. In this work an aeration process is simulated, where the air is injected from the bottom of a
cylindrical tank. Two numerical models are developed and two different geometries are considered.
Their results are verified against published data. Both models solve the momentum, continuity and k-
å equations for the relevant phases. The first model considers liquid and gas phases as homogeneous
fluid. The calculated velocity refers to the mixture of the phases. The second model assumes liquid and
gas as two distinct phases. Velocity and volume fraction profiles portray the induced motion of the liquid
and the extent of the aeration process. Regarding the two different geometries, the first assumes a
flat free liquid surface, while the second a liquid surface free to swell according to the gas injection rate.
It is shown that the second geometry gives more accurate results.