**Preface to "Industrial and Municipal Wastewater Treatment with a Focus on Water-Reuse"**

Population growth, climate change, but also rising prosperity are leading to increasing global water scarcity. Water shortages are thus hindering rural, urban and industrial development. Nowadays, approximately half of the world's population is affected temporarily by water scarcity. To enable a secure water supply, alternative water sources must be generated to tackle the challenge of water scarcity since ground and surface water sources are often overexploited. An important alternative resource is the reuse of treated wastewater. These days, water reuse processes are rarely considered and implemented. In contrast to the storage and use of rainwater, treated wastewater is a valuable resource, as it is available daily and in calculable quantities. Certain wastewater treatment processes within wastewater treatment plants are required to produce the new resource "reused water". The treatment processes depend on the quality of the wastewater inflow to the treatment plant since industrial and municipal wastewater flows are characterized, for example, by different concentrations. Moreover, water reuse methods must be developed in order to use the treated wastewater as efficiently as possible. Ideally, the reused water can be provided according to the "fit for purpose" principle and applied directly in areas such as irrigation, street cleaning, toilet flushing or make-up water for cooling systems.

The Special Issue "Industrial and Municipal Wastewater Treatment with a Focus on Water-Reuse" brings together new wastewater treatment technologies and emerging water reuse concepts to tackle the challenges of climate change with the aim of bringing the new resource "reused water" according to the "fit for purpose" principle to the subsequent user. This issue aims to draw on global experiences, approaches and solutions in the field of wastewater treatment and water reuse in rural, urban and industrial (park) areas. This allows a specific transferability to regions which have been subject to the long-term effects of climate change.

This book is focusing on the sections:

1. General challenges in the field of water scarcity, wastewater treatment and water reuse.

2. General approaches, processes, management and technologies in the field of municipal and industrial wastewater treatment and reuse.

3. Specific technologies for municipal and industrial wastewater treatment.

Regarding the first thematic part of the book the contribution of the Guest Editors Wagner and Bauer makes the prelude, in which different possibilities and challenges of the wastewater treatment and water reuse according to the status quo are presented. In addition, future needs and required innovations are also pointed out. The second paper by Zimmermann and Neu further addresses the challenges of water scarcity by providing a socio-ecological impact assessment and success factors of a water reuse system for irrigation purposes in central-northern Namibia. In order to achieve the best possible water quality from wastewater treatment plants, on the one hand to minimize the impact on surface waters, but also to prepare the water in the best possible way for water reuse, sustainable wastewater management is required. The article by de Anda and Shear presents therefore a sustainable wastewater management to reduce the freshwater contamination and water depletion in Mexico.

Concerning general approaches, processes, management and technologies in the field of municipal and industrial wastewater treatment and reuse the paper by Dawoud et al. deals with the optimization of wastewater treatment technologies in Qatar in order to reuse the wastewater, which is produced in high quantities in the industry, for irrigation purposes, among other things. Here, the analysis of the resulting sewage sludge also plays an important role. In the context of reusing treated wastewater, Albalasmeh et al. are focusing on the assessment of the effect of irrigation with treated wastewater on soil properties and on the performance of infiltration models. The contribution of Amann et al. extends the topic of wastewater treatment technologies by focusing not only on the removal of pollutants, but also on the recovery of resources from wastewater. In particular, the paper deals with operation and performance of Austrian wastewater and sewage sludge treatment as a basis for resource optimization. Beside all environmental aspects the financial feasibility is usually a concern in water reuse projects. Here, the paper by Intaraburt et al. investigated the influence of environmental benefits on the feasibility of water reclamation projects in industrial parks and focused on the case study in Chonburi, Thailand.

The third part of the book is focusing on specific technologies for municipal and also for industrial wastewater treatment. This section starts with Phan et al. which deals with Long-Term Toxicological Monitoring of a Multibarrier Advanced Wastewater Treatment Plant Comprising Ozonation and Granular Activated Carbon with In Vitro Bioassays. Nogushi et al. follow with Performance of Newly Developed Intermittent Aerator for Flat-Sheet Ceramic Membrane in Industrial MBR Systems. Reuse of Textile Dyeing Wastewater Treated by Electrooxidation is described by Pinto et al., followed by EL-Saeid et al. with the topic of Photo-Catalytic Remediation of Pesticides in Wastewater Using UV/TiO2. The removal of Carbamazepine by Clay-Based Materials Using Adsorption and Photodegradation is discussed by Levakov et al. Mosbah et al. are dealing with Ecological Synthesis of CuO Nanoparticles Using Punica granatum L. Peel Extract for the Retention of Methyl Green. Finally, Schestak et al. introduce a Calculator for the Environmental and Financial Potential of Drain Water Heat Recovery in Commercial Kitchens.

> **Martin Wagner and Sonja Bauer** *Editors*
