This title includes a number of Open Access chapters.

The activated sludge process is one of the most versatile and commonly used wastewater treatment systems in the world. In the past, when industrial wastewater treatment focused on removing biological oxygen demand and suspended solids, waste water plants needed different processes and technology. The shift to the activated sludge process means environmental engineers must build new treatment plants and retrofit old ones. In this compendium, the editor, an experienced and well-published scientist in the field, has brought together articles that relate to the new requirements.