Forward Osmosis as a Pre-treatment to Reverse Osmosis

This paper presents some aspects of forward osmosis coupled with reverse osmosis using a recirculating draw solution, to produce desalinated water or for dewatering/concentrating a feed stream, with some data provided from a number of operational sites. Many of these aspects are applicable to other osmotic processes and provide an insight into where they may be appropriately considered. A comparison is drawn between FO desalination and conventional reverse osmosis, from both real operational results and a theoretical comparison looking at the merits and demerits of the respective processes. This is of particular relevance when more complex pre and post treatments such as MF or UF and boron removal are applied to RO. Energy consumption figures with respect to the degree of fouling are presented, noting that both the practical and academic experience to date indicates that the FO process is much less prone to fouling than reverse osmosis. It is concluded that there are a number of differences that when taken as a whole can make a significant difference, primarily associated with reduced rates of fouling and the ability to operate the reverse osmosis step at optimum conditions. The International Desalination Association World Congress on Desalination and Water Reuse 2013 / Tianjin, China REF: IDAWC/TIAN13-318