## 1 Introduction  
During the last 50 years, the world's population has doubled and gross domestic production has increased ten folds, reflecting the underlying massive industrialization during this period. These developments have put the resources of freshwater, energy, and raw materials under ever-growing strain. Energy consumption has increased by five times during the last five decades and the majority of this energy consumption is coming from finite and polluting fossil fuels [1]. In the water sector, it has been estimated that two thirds of the world's population might be facing insufficient access to clean freshwater by 2025 [2]. Similarly, traditional mining is facing several environmental and sustainability related concerns. The scenario places an emphasis on sustainable industrial growth across the globe that can be realized by using the material and energy resources more efficiently and by exploiting the nontraditional but sustainable resources of these commodities while, at the same time, eliminating or minimizing the environmental hazards associated with the related processes [3]. These requirements clearly point out the urgency to develop new processes capable of producing and using energy, freshwater, and raw materials more efficiently and with the potential to exploit alternative resources of these products. Lack of a precise definition of sustainable development has resulted in the evolution of specific guidelines such as the PIS to implement the concept of sustainable development. Process intensification as defined by [PERSON] and [PERSON] [3,4] is the development of novel equipment and techniques that, compared to those commonly used, dramatically improve manufacturing and processing by decreasing substantially equipment size, improving raw material to production ratio, decreasing energy consumption and waste production, and that ultimately results in cheaper, efficient, safer, and more sustainable technologies. Modern membrane engineering represents one of the most interesting ways for developing processes in accordance with the guidelines provided by PIS to meet the challenges of the modern world [5; 6]. The main features of membrane engineering which make it perfectly aligned with PIS include its high selectivity and permeability for transport of specific components, the ease with which it can integrate with other processes or other membrane operations, its tendency to be less energy intensive and highly efficient, as well as its tendency to have low capital costs, small footprints, and high safety, operational simplicity, and flexibility [5; 7; 8; 9]. These exceptional features extend the sphere of applications of membrane engineering from water, energy, and raw materials sectors to sophisticated biomedical applications. Desalination represents one of the industrial sectors where membrane engineering has emerged as the key player to successfully implement the concept of PIS. In many parts of the world, conventional thermal desalination plants have been replaced with far less energy intensive, compact, and safer reverse osmosis (RO) units. Currently RO occupies more than a 60% share of the desalination market [10]. Thermal processes are limited only to the regions with abundant sources of fossil fuels, such as the Middle East. However, despite their loudly spoken advantages, the pressure driven processes face some challenges that hinder their wide spread and uniform growth in water stressed regions across the globe: operation at high pressure, high energy consumption, utilization of high grade energy, limited recovery factor (typically 40%-50%), and disposal of brine are the most significant obstacles that negatively affect the process economy and cause environmental problems. Several investigations have been carried out to tackle these challenges. These investigations have focused on improving the process performance of RO by optimizing the operating conditions and process design, by introducing a better control system, and by integrating the process with renewable energy resources.