Technology

Fast forward for desalination

 By Amanda Saint

At the 2015 Eni Awards, the Protection of the Environment Prize went to Professor Menachem Elimelech for his pioneering work in using Forward Osmosis to desalinate high salinity water…

Prof. Elimelech is the Roberto Goizueta Professor at the Department of Chemical and Environmental Engineering at Yale University. One of the world’s most cited researchers in the field of environmental engineering and science, he has published over 300 journal publications and was involved in the writing of two influential review articles that have shaped the research agenda in water purification and desalination in recent years.

To date, Prof. Elimelech has supervised 33 Ph.D. students and 26 postdoctoral researchers, many of whom now hold leading positions in academia and industry. In recognition of his excellence and dedication in teaching and mentoring, he received the W.M. Keck Foundation Engineering Teaching Excellence Award in 1994, the Yale University Graduate Mentoring Award in 2004, and the Yale University Postdoctoral Mentoring Prize in 2012.

One notable development of Prof. Elimelech and his current team of graduate researchers that led to the Eni 2015 Award was the novel ammonia carbon dioxide forward osmosis (FO) desalination processes, which uses low-grade heat as the source of energy to drive the separation process, thereby substantially decreasing the electric energy demand for desalination.

Eni Award 2015: interview with Menachem Elimelech

Forward osmosis exploits an osmotic gradient, which develops between two solutions of differing concentration, to effect efficient separation. Separating water and salt using reverse osmosis (RO) requires the application of a hydraulic pressure to drive flow against the osmotic gradient, which consumes a large amount of electric energy. In FO desalination, instead of hydraulic pressure, an osmotic pressure gradient between the saline feed and a highly-concentrated draw solution drives the flow of water across the membrane from the feed to the draw side. This means it’s easier to separate the salt from the water.

To work effectively, the draw solution used must generate a high osmotic pressure, be rejected by semipermeable membranes, and be easily separated from water. Prof. Elimelech and his team have developed the draw solution that meets all these criteria. What it all boils down to is that the FO desalination process advancements they have made enable clean drinking water to be produced with minimal electricity use.

Because thin-film composite reverse osmosis membranes are not suitable for FO, Prof. Elimelech has also developed the first thin-film composite FO membrane and demonstrated its high performance in the FO process. Oasys Water Inc. has licensed the invention from Yale University and developed a commercial FO membrane module, which it has launched alongside the commercialized FO desalination process. The commercialization of the FO technology will enable economically feasible and environmentally sustainable natural gas extraction, enabling us to continue to exploit it’s use for energy without detracting from our drive to cut greenhouse emissions.

The market for Oasys Water's commercial version of Prof. Elimelech is huge and as well as desalination, it appears that FO will be able to used for many other industrial applications, such as wastewater treatment to recover resources that can be used again, which would be difficult to achieve using conventional technologies

In August 2015, Oasys Water delivered the world’s first commercial application of FO technology for zero liquid discharge (ZLD) application at the Changxing Power Plant in Zhejiang Province, China. The hybrid treatment system treats waste water from the flue gas desulfurization (FGD) process and blowdown from the recirculating cooling systems of the coal-fired power plant. Current environmental regulations in China mean that all all coal-fired power plants are now required to have ZLD, and future regulations will also introduce this requirement for other types of industrial waste water.

So the market for Oasys Water’s commercial version of Prof. Elimelech is huge and as well as desalination, it appears that FO will be able to used for many other industrial applications, such as wastewater treatment to recover resources that can be used again, which would be difficult to achieve using conventional technologies.

Prof. Elimelech said of winning the award: “I feel humbled and honored to be the recipient of this prestigious award. I give credits to my current and former graduate students and postdocs who carried out their world-class research on this technology, and to Oasys Water Inc. for successfully commercializing the FO concept developed in our lab at Yale University.”So now that the process is commercialized, what’s the next step? “I continue to carry our research on membrane processes at the water-energy nexus, including on the process of forward osmosis. One of the relevant research areas that we are working on involves the development of high-performance membranes for FO, specifically developing membranes with higher water permeability and salt selectivity as well as membranes with resistance to fouling. Such membranes would significantly improve the efficiency of the FO process.”

about the author
Amanda Saint
Journalist and content writer, specialised in engineering and technology with a focus on environmental sustainability, urbanisation and biotechnology.