Per-and polyfluoroalkyl substances (PFAS), which are present in many waters, have detrimental impacts on human health and the environment. Reverse osmosis (RO) and nanofiltration (NF) have shown excellent PFAS separation performance in water treatment; however, these membrane systems do not destroy PFAS but produce concentrated residual streams that need to be managed. Complete destruction of PFAS in RO and NF concentrate streams is ideal, but long-term sequestration strategies are also employed. Because no single technology is adequate for all situations, a range of processes are reviewed here that hold promise as components of treatment schemes for PFAS-laden membrane system concentrates. Attention is also given to relevant

Commons Attribution (CC BY) license, which allows users to download, copy and build upon published articles, as long as the author and publisher are properly credited, which ensures maximum dissemination and a wider impact of our publications. Preface to "Membranes for Water and Wastewater Treatment"Water is a vital element for life and the environment. The vast majority of water on the Earth's surface (96%) is saline water in the oceans, and only a small volume of water has the right qualities to be consumed as drinking water. Water pollution has been documented as a contributor to a wide range of health problems. In recent years, the water quality levels have greatly deteriorated because of rapid social and economic development and because it is used as a "dump" for a wide range of pollutants.Many technologies have been developed to remove these pollutants. Among the different available treatments, "membrane technology" is one of the most viable alternatives, as it achieves high removal yields and has low costs. For this reason, membrane separation processes play an important role in water and wastewater treatment. Different membrane processes, including microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), reverse osmosis (RO), and forward osmosis (FO), have been used to treat water and wastewater. Besides these, membrane bioreactors (MBRs) have great potential for the treatment of municipal and industrial wastewater. In the last decade, new materials and fabrication processes have been developed to improve the performance of membrane synthesis and membrane-modification processes. This Special Issue aims to cover recent developments and advances in all aspects of membrane and wastewater treatment, including membrane processes, combined processes (including one membrane step), modified membranes, new materials, and new technologies to reduce fouling and to improve the efficiency of enhanced processes. This book aims to reach researchers and students in the membranes field who are interested in recent studies about membranes for water and wastewater treatment.The authors acknowledge Mr. Ian Tu as the assistant editor in the first step of this Special Issue and Mrs. Jasmine Xu, who has invested a lot of time and effort into the development of this project.

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Introduction. Understanding of crystal growth mechanism enables to develop efficient tools to control scaling and improve the process of treatment using membranes and increasing the amount of filtrate output. This investigation is aimed at studying an antiscalant behaviour in reverse osmosis (RO) process when treating ground water. Experimental dependences of calcium carbonate scaling efficiency on antiscalant dosage were found. Rates of adsorption on crystal surface of scaling deposit and on membrane surfaces were compared. Dependences of rates of inhibitor adsorption on crystal surface versus scaling rates were determined. Inhibitor adsorption on RO membrane surfaces was studied. New approaches to studying crystal growth mechanism in the presence of polymeric inhibitors are presented. Materials and methods. In the course of experiments conducted with using inhibitor dissolved in distilled water, inhibitor sorption on membrane surface was observed in the absence of calcium ions. As to experiments with dosing the inhibitor in tap water, the inhibitor sorption on the membrane did not occur: the inhibitor was adsorbed on the surface of the scaling crystals. Results. Experimental relationships are obtained that show dependencies of calcium carbonate deposit growth rates versus RO facility filtrate output values in the presence of different antiscalants with their dose values of 3, 5 and 7 mg/l. The article shows that antiscalant dose value does not provide substantial influence on antiscalant efficiency when natural water with low hardness is treated in the RO facility. This permits substantial reduction of operational costs. It was also proved that inhibitor is not adsorbed on membrane surface during natural water treatment that also confirms efficiency of low antiscalant dosing. Conclusions. Low hardness values of natural water (3–5 mill equivalents per liter) demonstrate that antiscalant efficiencies do not depend on its dose. Rate of inhibitor adsorption on crystal surface during calcium carbonate deposition also increases with scaling rate increase. Rates of antiscalant consumption increase with antiscalant dose values. In natural water the dissolved antiscalant molecules are bonded with calcium ions therefore antiscalant does not react with membranes and is not adsorbed on membrane surface.

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