The new edition of this book, written for both microbiologists and engineers, has been updated with the enormous amount of information made available in the past 6-7 years. The contributors are all internationally recognized as leading research workers in activated sludge microbiology, and all have made valuable contributions to our present understanding of the process. The Microbiology of Activated Sludge critically reviews our current understanding of the microbiology of activated sludge, the most commonly used method for treating both domestic and industrial wastes. It pays particular attention to how the application of molecular methods has changed our perceptions of the identity of the filamentous bacteria causing the operational disorders of bulking and foaming, and the bacteria responsible for nitrification and denitrification and phosphorus accumulation in nutrient removal processes.