Various concentrations of grease were fed to a completely mixed activated sludge laboratory plant and the effects of blending and the addition of a surfactant on removal efficiencies were determined. Blended and unblended raw sewage containing grease was studied to obtain a comparison between the removal efficiencies by organisms acclimated to a synthetic substrate and organisms naturally present in raw sewage. Grease determinations were made by a modification of Loehr and Rohlich's wet analysis method using chloroform as the solvent. The experimental results indicated that grease was readily metabolized by the organisms of activated sludge, that the addition of a surface active agent decreased the removal efficiency, and that blending of raw sewage prior to biological treatment should increase removal efficiencies to greater than 90 per cent. / Master of Science