Seawater desalination by electrodialysis. Part II: a novel approach to combat scaling in seawater desalination by electrodialysis

Abstract Elelctrodialysis is a well accepted process for brackish water desalination but has been considered prohibitively expensive for desalination of seawater due to high energy consumption. With the development of newer and more efficient membranes and improvements in stack design, we felt a need for a fresh look at electrodialysis for desalination of seawater. We thus developed an electrodialysis process using novel methods of stack design and employing dilute sulphuric acid and reject water from concentrate stream as electrode wash feed. The acidity built up in the concentrate compartment, probably due to conversion of MgCl2 into HCl and transport of H+ ions from anode compartment to concentrate stream, prevents any scale formation in the concentrate compartments, thus avoiding reversal of polarity or the need for chemical dosing. The recovery of water is more than 50% at an energy requirement for desalination alone in the range of 14–16 kWh/m3 of product water.