All suspended growth bio-oxidation systems can be viewed as modifications of the conventional activated-sludge process. Extensive use of several operational modes in recent years and introduction of the pure oxygen and activated biofilter (ABF) processes have led to some confusion as to the range of conditions for which a particular suspended growth process is best suited, the constraints placed on process choice by effluent standards, and the stability of various processes. This confusion can result in inappropriate process selection, overreliance on manufacturers’ claims, misapplication of processes, and, ultimately, transfer of the confusion to plant operators. The objective of this paper is to describe recently developed processes or modifications with respect to their unique advantages and disadvantages.