Modern industries demand large quantities of water at purity levels that are unprecedented in industrial applications. Unless water usage is changed, these processes will not be sustainable. The key solution to reducing water usage and wastewater discharge in the ultra-pure water (UPW) plants is the development of suitable technology for water reuse and recycling. In particular, successful water conservation strategies will require innovations in a number of areas. The ultimate solution to water conservation and sustainability for industrial use lies in some form of reuse and recycling strategy. However, the recycling process is not trivial and involves some challenges. Typically, the success in implementing recycling depends on two major factors: The first requirement would be the availability of robust and low-energy purification processes. This is critical because the environmental issues associated with water usage and wastewater discharge cannot be solved simply by recycling water if the recycling process consumes large amounts of energy. Large energy usage, in addition to being costly, would cancel any environmental gains that may be achieved by water saving. There is no merit in water recycling if for every unit of water recovered and recycled we end up using large amounts of energy. This is particularly important because many of the existing purification methods were not originally developed and optimized to accommodate recovery and reuse. In this article, some novel approaches and technologies based on the use of hybrid systems, their principle of operation and design, as well as the methods for selection and optimization of these promising hybrid systems are presented. The second requirement is the availability of fast-response, real-time, and on-line sensors, and the associated process control strategies to monitor the quality of purified wastewater and protect the system against any unexpected upsets or surges in impurities. In particular, there is a need for robust metrology methods to prevent potential risks associated with water recycling as well as to demonstrate that recycling, when properly designed and implemented, can save water, reduce cost, and improve water quality. The concept of comprehensive and integrated metrology combined with process control is key in both performance improvement and in cost reduction. The application of sensors and advanced process-control are particularly critical for the operation of the hybrid systems. The available technologies in this area, as well as the remaining challenges that would need further research and development, are reviewed.
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