Energy recovery for membrane desalination

The subject of energy recovery for seawater membrane desalination has been in a constant state of flux for all of the years since the inception of the concept of using reverse osmosis for desalination. Due to the high costs associated with the operation of these facilities, a way to recoup some of those costs to improve the operational economics has been a high priority. In this paper we discuss the historical changes associated with the variety of energy conservation technologies as well as the operational differences between them. We also look into the relative efficiencies of the technologies available and the design considerations of using these devices. Much of the focus of this dissertation will be the recent changes in technology which have drastically lowered the operational energy requirements for the highpressure reverse osmosis process. These newest developments will help to bring the widespread use of membrane desalination to the forefront of potable water production in the new millennium.

What can be concluded from this information? Since no device (mechanical or electrical) can realistically achieve 100% efficiency, and these newest energy recovery technologies are testing themselves at efficiencies up to 94%, there can only be marginal advances in this field in the future. As acceptance of this technology advance grows, this new technology should become the industry standard for the coming years as it builds a track record and acceptance based on cumulative long-term data as well as efficiency and longevity. The trend towards BOO- and BOOT-type contracts will also create strong incentives to minimize water cost by any and all means available, which will compound the growing demand for efficient operation of seawater desalination systems. The need for inexpensive and energy-efficient desalinated water grows with every year. The number of polluted or unusable water supplies, mixed with the known population growth and the advent of tourist enterprises in previously undeveloped areas, is making desalination not only a reality but also a necessity. With only 1% of the world’s water available as fresh water, and 97% of the world’s water as seawater, it is easy to determine the direction in which we as a species are headed with regard to water. As United States President John F. Kennedy said in 1961: “… if we could ever competitively, at a cheap rate, get fresh water from salt water, … [this] would be in the long-range interests of humanity which would really dwarf any other scientific accomplishment.” Many believe this statement is still valid today, 38 years later. Can this really be that much farther away?