This book simplifies microbiological processes involved in wastewater treatment to engineering students. It offers students a basic understanding of microbiology from an engineering perspective, in addition to metabolic (biological) reactions, microbial kinetics, and bioreactor processes so they can design wastewater treatment systems themselves. The book adopts lucid writing style that enables students to understand the theoretical concepts easily and contains many calculation-based problems with solutions provided in simple and clear way. The book is intended for undergraduate and graduate students of environmental engineering, chemical engineering, biotechnology and other allied majors.