(411b) Applications of Mean Age Theory to Mixing in Wastewater Treatment Facilities

Mixing operation is essential to wastewater treatment facilities. In most such facilities efficient mixing is required to homogenize mixtures, maximize contacts between constituents, prevent solid settling, etc. Different types of mixing devices are used to achieve these objectives, such as agitated impellers, jet mixers, floating mixers, static mixers, and other custom designed mixing systems. The design and selection of a mixing system has been mainly based on past experience and a quantitative method has been lacking. More recently, CFD modeling techniques have been used to facilitate the design process but most of such applications have been limited to fluid flow patterns.

In this talk, a quantitative method using CFD tools to design a mixing system will be discussed. The method is based on the 3D solution of mean age distribution. This method can be used to quantitatively measure either a batch system or a continuous system. The spatial distribution of mean age reveals the non-uniform distribution of local blend time thus any bypassing or dead zones can be easily located and quantified. The statistical analysis of mean age distribution provides quantitative comparisons of mixing efficiency of different mixing designs and guides the selection of an optimal design. Several examples of applying mean age method to mixing problems in wastewater treatment will be discussed in the talk.