The biennial International Gothenburg Symposia on Chemical Water and Waste­ water Treatment have proven to be a unique platform for the exchange of ideas and experiences between administrators, engineers and scientists active in the fields of water supply, wastewater disposal and pollution control. The First Symposium (Gothenburg, 1984) provided a long needed survey over theory and application of chemical water and wastewater treatment. The Second Symposium (Berlin, 1986) was devoted to aspects of recycling in chemical water and wastewater technology. The Third Symposium (Gothenburg, 1988) recognised the growing need and the potentials of pretreatment. These proceedings of the 4th Symposium focus on technology transfer from chemical treatment theory to practical treatment of drinking water and industrial or domestic wastewater. The contributions are devoted to questions of floc for­ mation and floc separation as well as problems and practical solutions associated with chemicals and dosing control. Special attention is given to the combination of chemical and biological processes for nutrient removal from wastewater. It is the editors' privilege to acknowledge the invaluable help from the authors of this book. It is the editors' hope that they might convey the significance and potential of chemical treatment in solving the challenging problems water purification, wastewater disposal and pollution control.