Decreasing Seawater Desalination Footprint by Integrating Bipolar-Membrane Electrodialysis in a Single-Pass Reverse Osmosis Scheme

Abstract

Reverse osmosis (RO) is currently the most cost-efficient method for seawater (SW) desalination; however, producing high-quality water with a low boron concentration typically requires a two-pass process, which increases the required area and chemical consumption. We propose a sustainable and economic pathway for boron removal in a single RO step, thus reducing the area footprint. At the same time, chemicals are produced onsite from the RO brine using bipolar membrane electrodialysis (BMED), thus reducing the chemical footprint. We conducted BMED using natural and synthetic feed solutions and studied the acid and base production kinetics and electricity consumption to assess the feasibility. In terms of energy efficiency, the divalent cationic impurities in the feed are more detrimental than the anionic ones. We found that monoselective cation-exchange membranes are not efficacious in eliminating these, and hence, precipitation/nanofiltration before BMED is essential. As a BMED feed, the nanofiltered SWRO brine was the best option over SW or nanofiltered SW. Economical analysis shows that as compared to purchasing chemicals, BMED integration can reduce the process cost by 45%. In addition, the results point to the flexibility of the proposed design that increases its robustness toward fluctuation in chemicals and electricity prices.