Book excerpt: The activated sludge process is the most versatile, commonly used wastewater treatment system in North America; however, many activated sludge processes frequently experience operational problems related to poor compaction or settleability of secondary solids and loss of secondary solids from the clarifier. Eschewing the technical jargon and copious chemical equations found in the majority of wastewater studies, Settleability Problems and Loss of Solids in the Activated Sludge Process speaks directly to plant operators, showing them how to identify and solve common problems and achieve maximum efficiency. Michael H. Gerardi’s hands-on guide addresses the most common plant operational problems, such as increased costs, loss of treatment efficiency, and permit violations. Using numerous tables and illustrations, Settleability Problems provides microscopic and analytical techniques for troubleshooting and identifying the conditions responsible for settleability problems and loss of solids. It includes pictures of wet mounts and smears of acceptable and unacceptable microscopic conditions of the activated sludge and presents corrective measures for operational problems. Chapters include: Undesired Filamentous Growth Nutrient-Deficient Floc Particles Denitrification Slug Discharge of Soluble cBOD Viscous Bulking or Zoogloeal Growth Production and Accumulation of Foam and Scum Volume II in the series, Settleability Problems will prove to be of unparalleled value to wastewater treatment plant operators as well as students of wastewater microbiology.