Hybrid Desalination SystemsHybrid processes consisting of electrodialysis (ED) and reverse osmosis (RO) or ED, RO, and distillation offer many advantages over traditional stand-alone applications of these technologies for desalination. Hybrid process configurations allow:
- More efficient operation of the ED process since ED efficiency decreases with decreasing diluate (product) concentration; the ED process is only utilized to partially reduce the concentration of the feed rather than produce a very low concentration finished product.
- Higher recovery, single pass RO system operation since the RO feed (ED diluate) concentration is already reduced by the ED process.
- Recycling of the RO concentrate to the ED process, reducing feed flow rate and pretreatment costs and the amount of concentrate requiring disposal.
- In ED/RO/distillation systems, further desalination of the ED concentrate stream by distillation to reduce concentrate volume and decrease overall feed flow rates.
- Blending of ED, RO, and/or distillation product waters to produce the final water quality desired.
In addition, coupling of other processes with RO also offers a solution to an increasingly important issue: disposal of concentrate generated by RO. This highly concentrated brine can be difficult to dispose, especially at inland desalination plants. Recycle of the concentrate to the ED cells, as well as use of distillation, can greatly reduce the quantities of concentrated brine that must be managed. The most efficient and economical hybrid processes involving ED, RO, and distillation depend on the feed and the final product quality required. Since limited data on these types of hybrid systems are available, selection, evaluation, and optimization are best performed using bench or pilot scale testing on the feed stream of interest.
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