With high-rate activated sludge as feed, various modes of digestion were studied on a laboratory scale at 20, 10, and 5 °C. This study was performed to develop design guidelines, operating criteria, and kinetic coefficients for low-temperature aerobic sludge digestion. To develop a possible scale factor for extrapolation of laboratory results to full-scale conditions, a field evaluation program was conducted to collect and analyze full-scale data from three independent sources.In this manuscript a summary of previously published data, as well as some of the latest research findings, have been presented. In addition, this paper outlines a new design procedure for use in "sizing" a typical aerobic digester; as well, a method for determination of oxygen requirements in the digester tanks is described.This design procedure is based primarily on a graphical solution involving several variables, whereby the percentage reduction of volatile suspended solids is plotted against the product of temperature and sludge age. Included in this presentation is a comparison between the use (and misuse) of kinetic data in traditional design procedures. The design methodology presented has already proven to be a valuable and cost-effective tool, especially for cold-climate package plant design.