Principles of Environmental Engineering is intended for a course in introductory environmental engineering for sophomore- or junior-level students. The emphasis of this text is on engineering principles rather than on engineering design. Students should understand such calculus topics as differentiation, integrations, and differential equations. Principles places more emphasis on scientific principles, ethics, and safety, and focuses less on engineering design. The text exposes students to a broader range of environmental topics through separate chapters on ecosystems, geological and soil resources, and agricultural effects. This new edition includes a new chapter on Biology, updated science and technology discussions to reflect the latest trends and new case studies in each chapter.