Proceedings

At Minworth STW it was proposed that settled sewage and Return Activated Sludge was to be
distributed to 24 aeration lanes via a distribution chamber comprising 24 Venturi flumes. It was
therefore required that there would be a reasonably uniform distribution of fluid and solids to each
flume. To determine whether this would be the case, computational fluid dynamic modelling was used
with a multiphase free surface model augmented with an algebraic slip scalar to represent the solids.
Since the fluid velocities are significantly higher than in a gravity settler where the solids may be
assumed to slip in the direction of gravity only, it was required that the solids may also slip at 90° to
the fluid streamline due to pressure forces resulting from streamline curvature. This paper describes
how this was achieved with a drag law and particle length scale for a non-Newtonian sludge where
the settling velocity is a function of the sludge concentration as defined by the Takacs settling
relationship.

KEYWORDS
Algebraic slip model, hindered settling, activated sludge, computational fluid dynamics