Solution to the boundary-value problems of non-uniform axial mixing in tapered aeration

The effect of axial mixing in an aeration tank of activated sludge process operating with a mode of tapered aeration has been studied from the view point of a heterogenous system. The dispersion model is applied to represent the flow system with tapered aeration, by which a formation of non-uniform axial mixing with an abrupt change of mixing intensity at the section-boundary is assumed.A numerical technique for solving the multi-point boundary-value problem associated with the system-model of tapered aeration is specifically introduced. By using this computational scheme, several simulations with different operating conditions resulting in various patterns of axial mixing; heterogenous, homogeneous, non-uniform and uniform axial mixing, are carried out.