Salinity Gradient Processes: FO and PRO – Are They Really the Answers to Desalination and Sustainable Energy Production?

Dr. Sarper Sarp
Swansea University, UK

By Dr. Sarper Sarp, Swansea University, UK.
Editor-in-Chief of Case Studies in Chemical and Environmental Engineering (Elsevier)
Editorial Board Member of Desalination (Elsevier).

Forward Osmosis (FO) has been considered as low energy alternatives to reverse osmosis for desalination. However, there are thermodynamic and mechanical limitations when it comes to the application of FO in the real world. The main difference between a modern PRO and an FO process is the applied pressure on a high salinity draw solution in the PRO process. The FO process has been considered as a lower energy desalination process where the source water salinity is above 50,000 mg/l, which makes FO a site/condition specific desalination application. However, PRO can be applied to any existing and new membrane based desalination system as an energy production or conservation process. The pressure of a high salinity draw solution can be kept relatively constant during the PRO process, even though the volumetric flow rate is to be increased. Therefore, the draw side of the PRO process can be assumed to be isobaric, in most cases. The harvested Gibbs free energy of mixing and volumetric expansion can explain the near-isobaric behaviour of the draw side of the PRO process. Thus, PRO can be used to multiply the internal energy of the draw solution with respect to the ratio of the permeated water flux. In this talk, I will explain the thermodynamic background of the salinity gradient processes and try to find an answer to their limitations.


Dr. Sarper Sarp is a lecturer at Chemical Engineering, at Swansea University. His research interests include salinity gradient systems, seawater pre-treatment, and solar desalination. Dr. Sarp obtained his Ph.D. in Environmental Science and Engineering at the Gwangju Institute of Science and Technology (GIST), South Korea, after receiving both his B.Sc. and M.Sc. degrees in Chemical Engineering from Ege University, Turkey. During his Ph.D. studies, he worked as a research associate at Southern Nevada Water Authority (SNWA), Las Vegas, and as a part time instructor at the University of Las Vegas Nevada (UNLV). Previously, Dr. Sarp was a Senior Scientist at QEERI, Qatar. Dr. Sarp is the author/co-author of over 25 peer reviewed articles, 1 book, 4 book chapters, and 5 intellectual properties. Dr. Sarp is also the Editor-in-Chief of the Case Studies in Chemical and Environmental Engineering (CSCEE – Elsevier) and a member of the Editorial Board of Desalination Journal (Elsevier).