Preface: Wastewater treatment and reuse—Present and future perspective on technological developments and management issues

The contributions of this book deal with some of the key topics relating to the reuse of reclaimed water projects, which, in many cases, are addressed together with the presentation of some case studies: regulation development, future perspectives, drivers, challenges and circular economy. The first two chapters focus on the evolution of the regulation at European level and in California and also discuss the main pillars achieved in these two contexts and the corresponding future perspectives. The third chapter provides an in-depth analysis of the pressure of agriculture on renewable water resources and the potential associated with reclaimed water reuse to cope with this pressure in the context of twenty Mediterranean countries. It also gives a brief overview of the RRW guidelines and regulations in these countries, discussing the main strengths and weaknesses of RRW in addressing water scarcity and climate change in the Mediterranean. Chapter four presents various case studies of the management and treatment of wastewater in Europe, Asia and Africa through the adoption of nature-based solutions and hybrid treatment systems which foster plant decentralization. It discusses how to redesign the (waste)water infrastructures in accordance with the principles of a circular economy while respecting environmental preservation and safeguarding. Four relevant case studies (among them Windhoek in Namibia) are the focus of chapter five which aims to highlight the drivers, challenges, opportunities, solutions and costs in water reuse projects and also to discuss the importance of considering transparency, accountability and participation for the proper governance of these projects. And lastly, chapter six deals with the role of water reuse in the panorama of a circular economy and it argues how it is possible to close the loop in water management by using the same words as the authors of this chapter: “the transition to a circular economy has the potential to transform current barriers to water reuse” and to promote these kinds of projects. The book represents an opportunity for scientists, practitioners, university students, decision makers and all readers interested in understanding how actions related to the reuse of reclaimed water can help to preserve freshwater and safely exploit treated domestic effluent for its direct reuse, which could be the main obstacles in such efforts, and it also details the directions outlined by current legislation.