The benefits of hybridising electrodialysis with reverse osmosis

Abstract

A cost analysis reveals that hybridisation of electrodialysis with reverse osmosis is only justified if the cost of water from the reverse osmosis unit is less than 40% of that from a standalone electrodialysis system. In such cases the additional reverse osmosis costs justify the electrodialysis cost savings brought about by shifting salt removal to higher salinity, where current densities are higher and equipment costs lower. Furthermore, the analysis suggests that a simple hybrid configuration is more cost effective than a recirculated hybrid, a simple hybrid being one where the reverse osmosis concentrate is fed to the electrodialysis stack and the products from both units are blended, and a recirculated being one hybrid involving recirculation of the electrodialysis product back to the reverse osmosis unit. The underlying rationale is that simple hybridisation shifts salt removal away from the lowest salinity zone of operation, where salt removal is most expensive. Further shifts in the salinity at which salt is removed, brought about by recirculation, do not justify the associated increased costs of reverse osmosis.

A new reverse electrodialysis design strategy which significantly reduces the levelized cost of electricity

“…We use a capital cost figure for the RED stack K mem of 750 $/m 2 [20,21]. Here, we assume that RED capital costs scale solely with membrane area and are similar to ED capital costs.…”

Optimal design and operation of electrodialysis for brackish-water desalination and for high-salinity brine concentration

“…ED has successfully been used for the desalination of brackish water [1][2][3][4][5][6][7][8][9], and for the concentration of seawater [10,11] or reverse-osmosis brine for salt production [1,12,13]. Despite the large number of studies published on ED, only a small number of these has analyzed the optimal design and operation of ED systems, with the bulk of the work being focused on brackish-water desalination.…”

The cost effectiveness of electrodialysis for diverse salinity applications

“…Relative to stack power consumption, pumping power is most significant at low diluate salinity where the current density and hence the stack power density is small. That pumping power is a low fraction of total power at low salinity thus suggests that this should also be the case at higher salinities [7,24].…”