Includes bibliographical references.

This investigation was undertaken with the objective of determining the importance of the initial mixing step in water and wastewater treatment processes and determining whether increasing the rapidity of the initial mixing could improve process performance. The principal process considered was alum coagulation-flocculation of a kaolin suspension in water. the initial mixing device under consideration was a biplane, square-mesh grid of bars placed in a turbulent flow, tubular reactor; a 2-in. pipe was used in the present studies. Studies were made using a single electrode "point" conductivity probe and NaCl solution tracer to determine what parameters affect the mixing which occurs in the turbulent flow field downstream from a grid, and from these results a general mixing model was developed. The relation between initial mixing and process performance was studied by using two of the grids from the mixing studies as initial mixing devices in coagulation of a kaolin suspension.