Abstract
In the past few decades, membrane-based processes have become mainstream in water desalination because of their relatively high water flux, salt rejection, and reasonable operating cost over thermal-based desalination processes. The energy consumption of the membrane process has been continuously lowered (from >10 kWh m−3 to ~3 kWh m−3) over the past decades but remains higher than the theoretical minimum value (~0.8 kWh m−3) for seawater desalination. Thus, the high energy consumption of membrane processes has led to the development of alternative processes, such as the electrochemical, that use relatively less energy. Decades of research have revealed that the low energy consumption of the electrochemical process is closely coupled with a relatively low extent of desalination. Recent studies indicate that electrochemical process must overcome efficiency rather than energy consumption hurdles. This short perspective aims to provide platforms to compare the energy efficiency of the representative membrane and electrochemical processes based on the working principle of each process. Future water desalination methods and the potential role of nanotechnology as an efficient tool to overcome current limitations are also discussed.
Highlights
Membrane processes have accelerated industrial use and research on water desalination owing to relatively low energy consumption (~4 kWh m−3 ) compared to previously used multiple-effect distillation and multi-stage flash thermo-based processes (>10 kWh m−3 ) [1,2]
The limited ion removal capacity of the electrochemical process implies that the overall productivity and energy efficiency and the energy consumption of the electrochemical and membrane processes should be compared [14,15]
Water molecules are transferred from the feed to the draw solution and drive a turbine to produce energy when the high-concentration solution is operated in a pressurized state in a process called pressure-retarded osmosis (PRO) (Figure 1c)
Summary
Membrane processes have accelerated industrial use and research on water desalination owing to relatively low energy consumption (~4 kWh m−3 ) compared to previously used multiple-effect distillation and multi-stage flash thermo-based processes (>10 kWh m−3 ) [1,2]. The limited ion removal capacity of the electrochemical process implies that the overall productivity and energy efficiency (according to the extent of desalination) and the energy consumption of the electrochemical and membrane processes should be compared [14,15]. An understanding of the process evaluation matrix (i.e., thermodynamic energy efficiency versus overall productivity) is needed to understand the direction of future desalination research From this perspective, a brief introduction of the membrane processes, the most widely employed desalination process, and its working principle are presented first. The future direction of water desalination technologies and the possible contribution of nanotechnology are discussed as efficient tools to overcome current limitations
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