The symposium whose papers are abstracted here was the fourth in a series held alternately at Kansas State University and the University of Nebraska–Lincoln. Requests for further information on projects conducted at Kansas State should be directed to Professor L.E. Erickson and on those at Nebraska to the editor.

Contents
John C. Heydweiller, "Estimating Sedimentation of Organisms in a Tower-Type Activated Sludge System"

Raymond C. Eliason, "Properties and Utilization of Small Particulates in Cattle Manure"

Kenneth H. Hsu, "Oxygen Transfer in Tower Systems with Motionless Mixers"

Raymond C. Eliason, "Hydrolysis of Sucrose by 20 Invertase Immobilized on Hollow Fibers"

Robert Shipman, "Single Cell Protein from Photosynthetic 26 Bacteria"

Peter J. Reilly, "Stability of Commensalistic Systems"