Water pollution occurs when toxic pollutants of varying kinds (organic, inorganic, radioactive and so on) are directly or indirectly discharged into water bodies without adequate treatment to remove such potential pollutants. Todays sources of these potential pollutants, which cause high deterioration of freshwater quality, are city sewage and industrial waste discharge, human agricultural practices, industrial waste disposal practices, mining activities, civil and structural work activities and obviously natural contamination with climate change. When our water is polluted, it is not only devastating to the environment but also to human health. Therefore, development of water and wastewater treatment processes to alleviate water pollution has been a challenging and demanding task for engineers, scientists and researchers. Perhaps this is even more challenging for underdeveloped and developing countries, where water and wastewater treatment facilities, knowledge and infrastructure are limited. Water and wastewater treatment processes are broad and often multidisciplinary in nature, comprising a mixture of research areas including physical, chemical and biological methods to remove or transform various potential pollutants. This is in hopes to achieve acceptable water quality and satisfy governmental and environmental protection agencies laws and regulations. With these objectives, this book has been written in order to provide various research results and compilation and up-to-date development on the current states of knowledge and techniques in the broad field of water and wastewater treatment processes. Basically, this book will give a comprehensive understanding and advancement and application of various physical, chemical and biological treatment methods in the reduction of potential pollutants (inorganics/organics) from water and wastewater. There are a total 18 book chapters contributed by large number of expert authors around the world, covering the following main research areas: Physical, chemical and biological water treatment processes such as adsorption, biosorption, coagulation/flocculation, electrocoagulation, denitration, membrane filtration/separation, photo-catalytic reduction, advanced oxidation, nutrients removal by struvite crystallisation and nanotechnology; Physical, chemical and biological methods for municipal wastewater and industrial wastewater treatment plants such as primary-secondary sludge treatments, anaerobic digestions, aerobic treatment, activated sludge processes, dewaterability by flocculants, pre-treatments of sludge and rheology of sludge in wastewater treatment; Various operational units/equipment and process control of wastewater treatment plant.