Clean water is one of the most important natural resources on earth. Wastewater, which is spent water, is also a valuable natural resource. However, wastewater may contain many contaminants and cannot be released back into the environment until the contaminants are removed. Untreated wastewater and inadequately treated wastewater may have a detrimental effect on the environment and has a harmful effect on human health. Water quality engineering addresses the sources, transport and treatment of chemical and microbiological contaminants that affect water. Objectives for the treatment of wastewater are that the treated wastewater can meet national effluent standards for the protection of the environment and the protection of public health. This book, which is based on the Special Issue, includes contributions on advanced technologies applied to the treatment of municipal and industrial wastewater and sludge. The book deals with recent advances in municipal wastewater, industrial wastewater, and sludge treatment technologies, health effects of municipal wastewater, risk management, energy efficient wastewater treatment, water sustainability, water reuse and resource recovery.