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Water, Water, Everywhere: Challenges of Inland Desalination: Feb. 4

Feb. 4, 2013 — 4:30 p.m., 216 Mann Hall, NC State University campus, Raleigh. See campus map.

Speaker:
2012/2013 AEESP Distinguished Lecturer Desmond Lawler
Nasser I. Al-Rashid Chair in Civil Engineering
Department of Civil, Architectural and Environmental Engineering
The University of Texas at Austin

Desalination is here. In the arid southwest, from Texas to California, as well as in Florida and a few other states, the demand for freshwater exceeds the supply. Fortunately, many of these regions have access to large brackish groundwater aquifers, and they are being tapped and desalted. In this age of sustainability, desalination presents particular problems, not only in the energy used to accomplish the desalination itself (where great progress has been made in the past 20 years), but in all of the ancillary processes. The central issue is recovery: the fraction of extracted water that becomes the product water. Recovery is limited because of the possibility of scale formation (precipitation of sparingly soluble salts) on the desalting membranes, a process that must be avoided. Pretreatment nearly always includes the application of anti-scalants (precipitation inhibitors), but can also include the precipitation of particularly undesirable constituents. The fraction that is not recovered is the concentrate, and its disposal in inland desalination is often expensive and sometimes problematic environmentally. Recovery is often limited to approximately 80% in conventional reverse osmosis (RO) systems, meaning that 20% of the water requires disposal.

Research in my group has included some work on pretreatment (particularly removal of silica, which can severely limit recovery) and more work on the treatment of concentrate to allow increased recovery. We have pursued two different avenues: (i) the deliberate precipitation of solids from the concentrate (with or without pre-oxidation of anti-scalants), followed by solid/liquid separation, with the liquid stream then available for further RO treatment, and (ii) the direct application of electrodialysis to RO concentrate to further increase recovery and thereby reduce the volume of concentrate. This talk will elucidate the general problems of inland desalination, and use examples from our research (as well as that of others) to illustrate the approaches to reduce these problems.

Co-hosted by the Department of Civil, Construction, and Environmental Engineering at North Carolina State University, the Department of Civil and Environmental Engineering at Duke University, and the Environmental Sciences and Engineering Department at the University of North Carolina at Chapel Hill.