Despite the tremendous improvements in conventional desalination technologies, its wide use is still limited due primarily to high energy requirements which are currently met with expensive fossil fuels. The use of alternative energy sources is essential to meet the growing demand for water desalination. In the last few decades a lot of effort has being directed in the use of different renewable energy (RE) sources to run desalination processes. However, the expansion of these efforts towards larger scale plants is hampered by several techno-economic challenges. Several medium-scale RE-driven desalination plants have been installed worldwide. Nevertheless, most of these plants are connected to the electrical grid to assure a continuous energy supply for stable operation. Furthermore, RE is mostly used to produce electric power which can be used to run desalination systems. This review paper focusses on an integrated approach in using RE-driven with an emphasis on solar and geothermal desalination technologies. Innovative and sustainable desalination processes which are suitable for integrated RE systems are presented. An assessment of the benefits of these technologies and their limitations are also discussed.

The approach of the present work is based on the use of poly (methylmethacrylate) (PMMA) polymer, which is compatible with PVDF and TiO2 nanoparticles in casting solutions, for the preparation of nano-composites membranes using a safer and more compatible solvent. TiO2 embedded poly (vinylidene fluoride) (PVDF)/PMMA photocatalytic membranes were prepared by phase inversion method. A non-solvent induced phase separation (NIPS) coupled with vapor induced phase separation (VIPS) was used to fabricate flat-sheet membranes using a dope solution consisting of PMMA, PVDF, TiO2, and triethyl phosphate (TEP) as an alternative non-toxic solvent. Membrane morphology was examined by scanning electron microscopy (SEM). Backscatter electron detector (BSD) mapping was used to monitor the inter-dispersion of TiO2 in the membrane surface and matrix. The effects of polymer concentration, evaporation time, additives and catalyst amount on the membrane morphology and properties were investigated. Tests on photocatalytic degradation of methylene blue (MB) were also carried out using the membranes entrapped with different concentrations of TiO2. The results of this study showed that nearly 99% MB removal can be easily achieved by photocatalysis using TiO2 immobilized on the membrane matrix. Moreover, it was observed that the quantity of TiO2 plays a significant role in the dye removal.

Abstract:The paper provides a critical overview of water desalination using geothermal resources. Specific case studies are presented, as well as an assessment of environmental risks and market potential and barriers to growth. The availability and suitability of low and high temperature geothermal energy in comparison to other renewable energy resources for desalination is also discussed. Analysis will show, for example, that the use of geothermal energy for thermal desalination can be justified only in the presence of cheap geothermal reservoirs or in decentralized applications focusing on small-scale water supplies in coastal regions, provided that society is able and willing to pay for desalting.

Recent trends and challenges in applications of INTRODUCTIONAdequate and dependable fresh water resources are major issues confronting many nations worldwide (Maila, 2006;Goosen et al., 2011aGoosen et al., & 2011bHuang, 2010; Lund, 2007; Mahmoudi et al., 2010a Mahmoudi et al., & 2010b. With the world's energy demand increasing much research has been directed at overcoming these challenges and in particular in using renewable energy to help meet the power needs for water desalination (Huang, 2010; Lund, 2007; Mahmoudi et al., 2010a;Serpen et al., 2010). However, Goosen (2012) and Gottinger and Goosen (2012) argued that while development opens up and advances economies, and creates new wealth, millions are forced to struggle to make meaning of the darker side of development that is not environmentally sustainable. In the past, the world's ecosystems (i.e. air, land and water) were able to absorb the environmental damage resulting from extensive industrialization and development. Nevertheless, with the rapid increases in global population and industrialization, as well as enhanced demands on natural resources such as fresh water supplies, the earth is no longer able to sustain a healthy and balanced ecosystem (Laboy-Nieves, 2009; Laboy et al., 2009; Mahmoudi et al., 2010a Mahmoudi et al., , 2010b Misra, 2000). The sustainability of the society in which we live is determined not only by technical and economic progress, but also by environmental management (Abdulla et al., 2009; Gottinger and Goosen, 2012; Laboy et al., 2010; Maila, 2006). Sustainable development using more renewable energy sources, by improving energy efficiency and reducing water demand and waste production is now considered by many as being the model to follow (Goosen et al., 2004; Goosen, et al., 2009aGoosen, et al., , 2009b Misra, 2000). Elimelech and Philip (2011), for example, reported on the possible reductions in energy demand by desalination technologies, and the role of innovative technologies in improving the sustainability of desalination as a technological solution to global water shortages ( Figure 1). They argued that future research to improve the energy efficiency of desalination should focus on, for example, the pre-treatment and posttreatment stages of seawater reverse osmosis (SWRO) plants. Furthermore, Peñate & García-Rodríguez (2012a) presented a comprehensive review of the main innovations and future trends in the design of SWRO desalination technology with an emphasis on improving process performance and efficiency. They concluded that desalination with renewable energies is an attractive combination that will help to reduce stress on existing water supplies.The economic potential and environmental benefits of renewable energies, such as geothermal, solar, wave and wind, and their applications to reducing overall energy requirements have been described in a number of recent articles (Cataldi, et al., 1999;Huang, 2010;Goosen et al., 2011b; Lund, 2007; Mahmoudi et al., 2010a;Serpen et al., 2010;Stefansson, 2005)....

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