Abstract: Our treatment of pollution-abatement engineering is offered in the belief that the trained engineer should more firmly understand fundamental principles, be more aware of the similarities and/or differences among many of the engineering systems, and exhibit greater flexibility and originality in the definition and innovative solution of environmental pollution problems.In short, environmental engineers should by conviction and practice be more readily adaptable to change and progress.Coverage of the unusually broad field of environmental engineering has demanded an expertise that could only be provided through multiple authorships.Each author (or group of authors) was permitted to employ, within reasonable limits, the customary personal style in organizing and presenting a particular subject area, and, consequently, it has been difficult to treat all subject material in a homogeneous manner.Moreover, owing to limitations of space, some of the authors' favored topics could not be treated in great detail, and many less important topics had to be merely mentioned or commented on briefly.All of the authors have provided an excellent list of references at the end of each chapter for the benefit of the interested reader.Because each of the chapters is meant to be self-contained, some mild repetition among the various texts was unavoidable.In each case, all errors of omission or repetition are the responsibility of the editors and not the individual authors.With the current trend toward metrication, the question of using a consistent system of units has been a problem.Wherever possible the authors have used the British system along with the metric equivalent or vice versa.The authors sincerely hope that this doubled system of unit notation will prove helpful rather than disruptive to the readers.The goals of the Handbook of Environmental Engineering series are: (1) to cover the entire range of environmental fields, including air and noise pollution control, solid waste processing and resource recovery, biological treatment processes, water resources, natural control processes, radioactive waste disposal, thermal pollution control, and physicochemical treatment processes; and (2) to employ a multithematic approach to environmental pollution control because air, water, land, and energy are all interrelated.The organization of the series is mainly based on the three basic forms in which pollutants and waste are manifested: gas, solid, and liquid.In addition, noise pollution control is included in one of the handbooks in the series.This volume, Physicochemical Treatment Processes, has been designed to serve as a basic physicochemical treatment text as well as a comprehensive reference book.We hope and expect it will prove to be of high value to advanced undergraduate or graduate students, to designers of water and wastewater treatment systems, and to research workers.The editors welcome comments from readers in all these categories.It is our hope that this book will not only provide information on the physical, chemical, and mechanical treatment technologies, but will also serve as a basis for advanced study or specialized investigation of the theory and practice of the individual physicochemical systems covered.The editors are pleased to acknowledge the encouragement and support received from their colleagues and the publisher during the conceptual stages of this endeavor.