The third in a series of publications on wastewater biology, this reference reviews the natural and wastewater environments or habitats of the microscopic and macroscopic organisms associated with wastewater treatment systems. Written with a minimum of technical jargon, the text provides not only an identification of commonly occurring organisms and their basic roles in wastewater treatment, but also a description of their habitats and the way these habitats and operational conditions interact. This book can be used as an operational and troubleshooting text, a reference text, or an educational resource.