Reverse osmosis (RO) is a widely used process for removing salt and other impurities from seawater, brackish water, and wastewater to produce clean drinking water, industrial process water, and boiler feed water. The process works by forcing water through a semipermeable membrane at high pressure, leaving behind the salt and other impurities. The traditional theory of how RO works is based on the solution-diffusion model, which assumes that the water molecules dissolve and diffuse through the membrane by way of their concentration gradient.
However, the recent study conducted by the team led by Prof. Menachem Elimelech challenges this conventional understanding of the theory of solution-diffusion and suggests an alternative theory that the water transport is driven by pressure changes within the membrane, rather than the concentration gradient of molecules. This new theory is based on computer simulations and experiments that show water molecules travel as clusters through a network of pores in the membrane, rather than separating from each other, as previously thought.
The research conducted by the team led by Prof. Menachem Elimelech and team—which included scientists from the University of Wisconsin-Madison and Texas Tech University challenges the conventional understanding of the theory of solution-diffusion, which has been widely accepted for over five decades to explain how reverse osmosis works. The study shows that reverse osmosis is driven by pressure changes within the membrane, rather than the concentration gradient of molecules, as previously thought. This new understanding can potentially lead to the development of more effective materials and techniques to improve the process of reverse osmosis for applications in water purification, wastewater treatment, and energy production.
The team used a combination of experiments and computer simulations to arrive at their findings, and their results were consistent with each other. The computer simulations of the molecules' movements showed that water transport is driven by changes in pressure within the membrane and that water molecules travel as clusters through a network of pores in the membrane. The experiments showed that water permeates the membrane depending on the membrane pore size, the size of the water molecules, and the viscosity of the water. These results are inconsistent with the solution-diffusion model and provide evidence to support the new theory proposed by the team.
One example of the implications of this new understanding is the development of more effective materials and techniques to improve the process of RO. For instance, the new theory suggests that optimizing the pore size of the membrane and the viscosity of the water can enhance the performance of the process. By creating membranes with smaller and more uniform pore sizes, water molecules can be forced to move through the membrane more efficiently, leading to a higher salt rejection rate and higher water recovery rate. Additionally, by using water with a lower viscosity, such as warm water, the pressure drop across the membrane can be reduced, improving the energy efficiency of the process.
Another example of the implications of this new understanding is the potential for developing new applications for RO. For instance, the ability to control water transport through membranes more precisely could enable the development of new technologies for capturing and converting energy. One such technology is pressure-retarded osmosis (PRO), which uses the pressure difference between seawater and freshwater to generate water. By improving our understanding of how water transport works through membranes, we may be able to develop more efficient PRO systems that can generate more water with less energy input.
inconclusion, the new theory proposed by the team led by Prof. Menachem Elimelech has significant implications for the field of RO and related technologies. By improving our understanding of how water transport works through membranes, we can develop more effective materials and techniques to improve the process and create new applications for the technology. it will help lower energy consumption of reverse osmosis.
you can find more information in this yale published article:Â Upending a decades-long theory of reverse osmosis water desalination (phys.org)
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