From the book's introduction: This is not an introductory text about activated sludge. In this book, we discuss the observation, testing, and calculation procedures that provide data about the status of the activated sludge process. In addition, we discuss in depth how to apply this data to the business of controlling your activated sludge treatment process.Basic activated sludge concepts are addressed in this book in the context of process evaluation and control. We focus our efforts on discussing a basic, practical system of control for the process.The procedures discussed in this manual are equally applicable to all variations. An operator must have information about settleability, dissolved oxygen concentration, solids concentration, effluent quality, and clarifier sludge levels for consistent, efficient process performance of every type of activated sludge process. These procedures are covered in detail.The procedures discussed are based on work done by E. B. Mallory in the 1930's and 40's and further developed by Alfred W. West while he was head of the Operational Technology Branch of the Environmental Protection Agency in the 1960's and 70's. The system, with some modifications by this author, is frequently called the "West Method" or "Sludge Quality Method" of activated sludge process control because operational controls adjustments are based on the sludge quality existing in your facility rather than on arbitrary values.